refactor: improve handling of optional CustomerID in project models and DTOs

.clinerules

@@ -37,6 +37,7 @@ SOLVE TASKS AS FAST AS POSSIBLE. EACH REQUEST COSTS THE USER MONEY.
 - Unexpected behavior is encountered
 - Specific conditions require warnings
 - New patterns emerge that need documentation
+- DO NOT FIX UNUSED IMPORTS - this is the job of the linter
 10.Implement a REST API update handling in Go using Gin that ensures the following behavior:
 - The update request is received as JSON.
 - If a field is present in the JSON and set to null, the corresponding value in the database should be removed.

.gitea/workflows/demo.yaml

@@ -0,0 +1,19 @@
+name: Gitea Actions Demo
+run-name: ${{ gitea.actor }} is testing out Gitea Actions 🚀
+on: [push]
+
+jobs:
+  Explore-Gitea-Actions:
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo "🎉 The job was automatically triggered by a ${{ gitea.event_name }} event."
+      - run: echo "🐧 This job is now running on a ${{ runner.os }} server hosted by Gitea!"
+      - run: echo "🔎 The name of your branch is ${{ gitea.ref }} and your repository is ${{ gitea.repository }}."
+      - name: Check out repository code
+        uses: actions/checkout@v4
+      - run: echo "💡 The ${{ gitea.repository }} repository has been cloned to the runner."
+      - run: echo "🖥️ The workflow is now ready to test your code on the runner."
+      - name: List files in the repository
+        run: |
+          ls ${{ gitea.workspace }}
+      - run: echo "🍏 This job's status is ${{ job.status }}."

backend/cmd/dbtest/main.go

@@ -7,6 +7,8 @@ import (
 	"log"
 	"time"
 
+	"github.com/timetracker/backend/internal/config"
+	"github.com/timetracker/backend/internal/db"
 	"github.com/timetracker/backend/internal/models"
 )
 
@@ -15,15 +17,15 @@ func main() {
 	flag.Parse()
 
 	// Get database configuration with sensible defaults
-	dbConfig := models.DefaultDatabaseConfig()
+	dbConfig := config.DefaultDatabaseConfig()
 
 	// Initialize database
 	fmt.Println("Connecting to database...")
-	if err := models.InitDB(dbConfig); err != nil {
+	if err := db.InitDB(dbConfig); err != nil {
 		log.Fatalf("Error initializing database: %v", err)
 	}
 	defer func() {
-		if err := models.CloseDB(); err != nil {
+		if err := db.CloseDB(); err != nil {
 			log.Printf("Error closing database connection: %v", err)
 		}
 	}()
@@ -34,7 +36,7 @@ func main() {
 	defer cancel()
 
 	// Get the database engine
-	db := models.GetEngine(ctx)
+	db := db.GetEngine(ctx)
 
 	// Test database connection with a simple query
 	var result int

backend/cmd/migrate/main.go

@@ -6,6 +6,8 @@ import (
 	"log"
 	"os"
 
+	"github.com/timetracker/backend/internal/config"
+	"github.com/timetracker/backend/internal/db"
 	"github.com/timetracker/backend/internal/models"
 	"gorm.io/gorm/logger"
 )
@@ -29,7 +31,7 @@ func main() {
 	}
 
 	// Get database configuration with sensible defaults
-	dbConfig := models.DefaultDatabaseConfig()
+	dbConfig := config.DefaultDatabaseConfig()
 
 	// Override with environment variables if provided
 	if host := os.Getenv("DB_HOST"); host != "" {
@@ -62,7 +64,7 @@ func main() {
 
 	var err error
 
-	gormDB, err := models.GetGormDB(dbConfig, "postgres")
+	gormDB, err := db.GetGormDB(dbConfig, "postgres")
 	if err != nil {
 		log.Fatalf("Error getting gorm DB: %v", err)
 	}
@@ -89,11 +91,11 @@ func main() {
 		fmt.Printf("✓ Database %s created successfully\n", dbConfig.DBName)
 	}
 
-	if err = models.InitDB(dbConfig); err != nil {
+	if err = db.InitDB(dbConfig); err != nil {
 		log.Fatalf("Error initializing database: %v", err)
 	}
 	defer func() {
-		if err := models.CloseDB(); err != nil {
+		if err := db.CloseDB(); err != nil {
 			log.Printf("Error closing database connection: %v", err)
 		}
 	}()

backend/cmd/modeltest/main.go

@@ -7,21 +7,23 @@ import (
 	"time"
 
 	"github.com/oklog/ulid/v2"
+	"github.com/timetracker/backend/internal/config"
+	"github.com/timetracker/backend/internal/db"
 	"github.com/timetracker/backend/internal/models"
 	"github.com/timetracker/backend/internal/types"
 )
 
 func main() {
 	// Get database configuration with sensible defaults
-	dbConfig := models.DefaultDatabaseConfig()
+	dbConfig := config.DefaultDatabaseConfig()
 
 	// Initialize database
 	fmt.Println("Connecting to database...")
-	if err := models.InitDB(dbConfig); err != nil {
+	if err := db.InitDB(dbConfig); err != nil {
 		log.Fatalf("Error initializing database: %v", err)
 	}
 	defer func() {
-		if err := models.CloseDB(); err != nil {
+		if err := db.CloseDB(); err != nil {
 			log.Printf("Error closing database connection: %v", err)
 		}
 	}()

backend/cmd/seed/main.go

@@ -7,6 +7,7 @@ import (
 	"log"
 
 	"github.com/timetracker/backend/internal/config"
+	"github.com/timetracker/backend/internal/db"
 	"github.com/timetracker/backend/internal/models"
 	"gorm.io/gorm"
 )
@@ -23,11 +24,11 @@ func main() {
 	}
 
 	// Initialize database
-	if err := models.InitDB(cfg.Database); err != nil {
+	if err := db.InitDB(cfg.Database); err != nil {
 		log.Fatalf("Error initializing database: %v", err)
 	}
 	defer func() {
-		if err := models.CloseDB(); err != nil {
+		if err := db.CloseDB(); err != nil {
 			log.Printf("Error closing database connection: %v", err)
 		}
 	}()
@@ -44,7 +45,7 @@ func main() {
 func seedDatabase(ctx context.Context) error {
 	// Check if seeding is needed
 	var count int64
-	if err := models.GetEngine(ctx).Model(&models.Company{}).Count(&count).Error; err != nil {
+	if err := db.GetEngine(ctx).Model(&models.Company{}).Count(&count).Error; err != nil {
 		return fmt.Errorf("error checking if seeding is needed: %w", err)
 	}
 
@@ -57,7 +58,7 @@ func seedDatabase(ctx context.Context) error {
 	log.Println("Seeding database with initial data...")
 
 	// Start transaction
-	return models.GetEngine(ctx).Transaction(func(tx *gorm.DB) error {
+	return db.GetEngine(ctx).Transaction(func(tx *gorm.DB) error {
 		// Create default company
 		defaultCompany := models.Company{
 			Name: "Default Company",

backend/internal/api/dto/project_dto.go

@@ -12,7 +12,7 @@ type ProjectDto struct {
 	UpdatedAt    time.Time `json:"updatedAt" example:"2024-01-01T00:00:00Z"`
 	LastEditorID string    `json:"lastEditorID" example:"01HGW2BBG0000000000000000"`
 	Name         string    `json:"name" example:"Time Tracking App"`
-	CustomerID   *string   `json:"customerId" example:"01HGW2BBG0000000000000000"`
+	CustomerID   *string   `json:"customerId,omitempty" example:"01HGW2BBG0000000000000000"`
 }
 
 type ProjectCreateDto struct {

backend/internal/api/dto/user_dto.go

@@ -13,7 +13,7 @@ type UserDto struct {
 	LastEditorID string    `json:"lastEditorID" example:"01HGW2BBG0000000000000000"`
 	Email        string    `json:"email" example:"test@example.com"`
 	Role         string    `json:"role" example:"admin"`
-	CompanyID    *string   `json:"companyId" example:"01HGW2BBG0000000000000000"`
+	CompanyID    *string   `json:"companyId,omitempty" example:"01HGW2BBG0000000000000000"`
 	HourlyRate   float64   `json:"hourlyRate" example:"50.00"`
 }
 

backend/internal/api/handlers/activity_handler.go

@@ -1,12 +1,13 @@
 package handlers
 
 import (
-	"net/http"
+	"context"
 
 	"github.com/gin-gonic/gin"
 	"github.com/oklog/ulid/v2"
+	"github.com/timetracker/backend/internal/api/dto"
+	"github.com/timetracker/backend/internal/api/responses"
 	"github.com/timetracker/backend/internal/api/utils"
-	dto "github.com/timetracker/backend/internal/dtos"
 	"github.com/timetracker/backend/internal/models"
 	"github.com/timetracker/backend/internal/types"
 )
@@ -32,20 +33,7 @@ func NewActivityHandler() *ActivityHandler {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/activities [get]
 func (h *ActivityHandler) GetActivities(c *gin.Context) {
-	// Get activities from the database
-	activities, err := models.GetAllActivities(c.Request.Context())
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving activities: "+err.Error())
-		return
-	}
-
-	// Convert to DTOs
-	activityDTOs := make([]dto.ActivityDto, len(activities))
-	for i, activity := range activities {
-		activityDTOs[i] = convertActivityToDTO(&activity)
-	}
-
-	utils.SuccessResponse(c, http.StatusOK, activityDTOs)
+	utils.HandleGetAll(c, models.GetAllActivities, convertActivityToDTO, "activities")
 }
 
 // GetActivityByID handles GET /activities/:id
@@ -64,30 +52,7 @@ func (h *ActivityHandler) GetActivities(c *gin.Context) {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/activities/{id} [get]
 func (h *ActivityHandler) GetActivityByID(c *gin.Context) {
-	// Parse ID from URL
-	idStr := c.Param("id")
-	id, err := ulid.Parse(idStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid activity ID format")
-		return
-	}
-
-	// Get activity from the database
-	activity, err := models.GetActivityByID(c.Request.Context(), types.FromULID(id))
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving activity: "+err.Error())
-		return
-	}
-
-	if activity == nil {
-		utils.NotFoundResponse(c, "Activity not found")
-		return
-	}
-
-	// Convert to DTO
-	activityDTO := convertActivityToDTO(activity)
-
-	utils.SuccessResponse(c, http.StatusOK, activityDTO)
+	utils.HandleGetByID(c, models.GetActivityByID, convertActivityToDTO, "activity")
 }
 
 // CreateActivity handles POST /activities
@@ -105,27 +70,7 @@ func (h *ActivityHandler) GetActivityByID(c *gin.Context) {
 //	@Failure		500			{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/activities [post]
 func (h *ActivityHandler) CreateActivity(c *gin.Context) {
-	// Parse request body
-	var activityCreateDTO dto.ActivityCreateDto
-	if err := c.ShouldBindJSON(&activityCreateDTO); err != nil {
-		utils.BadRequestResponse(c, "Invalid request body: "+err.Error())
-		return
-	}
-
-	// Convert DTO to model
-	activityCreate := convertCreateActivityDTOToModel(activityCreateDTO)
-
-	// Create activity in the database
-	activity, err := models.CreateActivity(c.Request.Context(), activityCreate)
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error creating activity: "+err.Error())
-		return
-	}
-
-	// Convert to DTO
-	activityDTO := convertActivityToDTO(activity)
-
-	utils.SuccessResponse(c, http.StatusCreated, activityDTO)
+	utils.HandleCreate(c, createActivityWrapper, convertActivityToDTO, "activity")
 }
 
 // UpdateActivity handles PUT /activities/:id
@@ -145,43 +90,7 @@ func (h *ActivityHandler) CreateActivity(c *gin.Context) {
 //	@Failure		500			{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/activities/{id} [put]
 func (h *ActivityHandler) UpdateActivity(c *gin.Context) {
-	// Parse ID from URL
-	idStr := c.Param("id")
-	id, err := ulid.Parse(idStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid activity ID format")
-		return
-	}
-
-	// Parse request body
-	var activityUpdateDTO dto.ActivityUpdateDto
-	if err := c.ShouldBindJSON(&activityUpdateDTO); err != nil {
-		utils.BadRequestResponse(c, "Invalid request body: "+err.Error())
-		return
-	}
-
-	// Set ID from URL
-	activityUpdateDTO.ID = id.String()
-
-	// Convert DTO to model
-	activityUpdate := convertUpdateActivityDTOToModel(activityUpdateDTO)
-
-	// Update activity in the database
-	activity, err := models.UpdateActivity(c.Request.Context(), activityUpdate)
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error updating activity: "+err.Error())
-		return
-	}
-
-	if activity == nil {
-		utils.NotFoundResponse(c, "Activity not found")
-		return
-	}
-
-	// Convert to DTO
-	activityDTO := convertActivityToDTO(activity)
-
-	utils.SuccessResponse(c, http.StatusOK, activityDTO)
+	utils.HandleUpdate(c, models.UpdateActivity, convertActivityToDTO, prepareActivityUpdate, "activity")
 }
 
 // DeleteActivity handles DELETE /activities/:id
@@ -199,22 +108,7 @@ func (h *ActivityHandler) UpdateActivity(c *gin.Context) {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/activities/{id} [delete]
 func (h *ActivityHandler) DeleteActivity(c *gin.Context) {
-	// Parse ID from URL
-	idStr := c.Param("id")
-	id, err := ulid.Parse(idStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid activity ID format")
-		return
-	}
-
-	// Delete activity from the database
-	err = models.DeleteActivity(c.Request.Context(), types.FromULID(id))
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error deleting activity: "+err.Error())
-		return
-	}
-
-	utils.SuccessResponse(c, http.StatusNoContent, nil)
+	utils.HandleDelete(c, models.DeleteActivity, "activity")
 }
 
 // Helper functions for DTO conversion
@@ -252,3 +146,35 @@ func convertUpdateActivityDTOToModel(dto dto.ActivityUpdateDto) models.ActivityU
 
 	return update
 }
+
+// prepareActivityUpdate prepares the activity update object by parsing the ID, binding the JSON, and converting the DTO to a model
+func prepareActivityUpdate(c *gin.Context) (models.ActivityUpdate, error) {
+	// Parse ID from URL
+	id, err := utils.ParseID(c, "id")
+	if err != nil {
+		responses.BadRequestResponse(c, "Invalid activity ID format")
+		return models.ActivityUpdate{}, err
+	}
+
+	// Parse request body
+	var activityUpdateDTO dto.ActivityUpdateDto
+	if err := utils.BindJSON(c, &activityUpdateDTO); err != nil {
+		responses.BadRequestResponse(c, err.Error())
+		return models.ActivityUpdate{}, err
+	}
+
+	// Set ID from URL
+	activityUpdateDTO.ID = id.String()
+
+	// Convert DTO to model
+	return convertUpdateActivityDTOToModel(activityUpdateDTO), nil
+}
+
+// createActivityWrapper is a wrapper function for models.CreateActivity that takes a DTO as input
+func createActivityWrapper(ctx context.Context, createDTO dto.ActivityCreateDto) (*models.Activity, error) {
+	// Convert DTO to model
+	activityCreate := convertCreateActivityDTOToModel(createDTO)
+
+	// Call the original function
+	return models.CreateActivity(ctx, activityCreate)
+}

backend/internal/api/handlers/company_handler.go

@@ -1,12 +1,12 @@
 package handlers
 
 import (
-	"net/http"
+	"context"
 
 	"github.com/gin-gonic/gin"
-	"github.com/oklog/ulid/v2"
+	"github.com/timetracker/backend/internal/api/dto"
+	"github.com/timetracker/backend/internal/api/responses"
 	"github.com/timetracker/backend/internal/api/utils"
-	dto "github.com/timetracker/backend/internal/dtos"
 	"github.com/timetracker/backend/internal/models"
 	"github.com/timetracker/backend/internal/types"
 )
@@ -32,20 +32,7 @@ func NewCompanyHandler() *CompanyHandler {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/companies [get]
 func (h *CompanyHandler) GetCompanies(c *gin.Context) {
-	// Get companies from the database
-	companies, err := models.GetAllCompanies(c.Request.Context())
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving companies: "+err.Error())
-		return
-	}
-
-	// Convert to DTOs
-	companyDTOs := make([]dto.CompanyDto, len(companies))
-	for i, company := range companies {
-		companyDTOs[i] = convertCompanyToDTO(&company)
-	}
-
-	utils.SuccessResponse(c, http.StatusOK, companyDTOs)
+	utils.HandleGetAll(c, models.GetAllCompanies, convertCompanyToDTO, "companies")
 }
 
 // GetCompanyByID handles GET /companies/:id
@@ -64,30 +51,7 @@ func (h *CompanyHandler) GetCompanies(c *gin.Context) {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/companies/{id} [get]
 func (h *CompanyHandler) GetCompanyByID(c *gin.Context) {
-	// Parse ID from URL
-	idStr := c.Param("id")
-	id, err := ulid.Parse(idStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid company ID format")
-		return
-	}
-
-	// Get company from the database
-	company, err := models.GetCompanyByID(c.Request.Context(), types.FromULID(id))
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving company: "+err.Error())
-		return
-	}
-
-	if company == nil {
-		utils.NotFoundResponse(c, "Company not found")
-		return
-	}
-
-	// Convert to DTO
-	companyDTO := convertCompanyToDTO(company)
-
-	utils.SuccessResponse(c, http.StatusOK, companyDTO)
+	utils.HandleGetByID(c, models.GetCompanyByID, convertCompanyToDTO, "company")
 }
 
 // CreateCompany handles POST /companies
@@ -105,27 +69,7 @@ func (h *CompanyHandler) GetCompanyByID(c *gin.Context) {
 //	@Failure		500		{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/companies [post]
 func (h *CompanyHandler) CreateCompany(c *gin.Context) {
-	// Parse request body
-	var companyCreateDTO dto.CompanyCreateDto
-	if err := c.ShouldBindJSON(&companyCreateDTO); err != nil {
-		utils.BadRequestResponse(c, "Invalid request body: "+err.Error())
-		return
-	}
-
-	// Convert DTO to model
-	companyCreate := convertCreateCompanyDTOToModel(companyCreateDTO)
-
-	// Create company in the database
-	company, err := models.CreateCompany(c.Request.Context(), companyCreate)
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error creating company: "+err.Error())
-		return
-	}
-
-	// Convert to DTO
-	companyDTO := convertCompanyToDTO(company)
-
-	utils.SuccessResponse(c, http.StatusCreated, companyDTO)
+	utils.HandleCreate(c, createCompanyWrapper, convertCompanyToDTO, "company")
 }
 
 // UpdateCompany handles PUT /companies/:id
@@ -145,40 +89,7 @@ func (h *CompanyHandler) CreateCompany(c *gin.Context) {
 //	@Failure		500		{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/companies/{id} [put]
 func (h *CompanyHandler) UpdateCompany(c *gin.Context) {
-	// Parse ID from URL
-	idStr := c.Param("id")
-	id, err := types.ULIDFromString(idStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid company ID format")
-		return
-	}
-
-	// Parse request body
-	var companyUpdateDTO dto.CompanyUpdateDto
-	if err := c.ShouldBindJSON(&companyUpdateDTO); err != nil {
-		utils.BadRequestResponse(c, "Invalid request body: "+err.Error())
-		return
-	}
-
-	// Convert DTO to model
-	companyUpdate := convertUpdateCompanyDTOToModel(companyUpdateDTO, id)
-
-	// Update company in the database
-	company, err := models.UpdateCompany(c.Request.Context(), companyUpdate)
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error updating company: "+err.Error())
-		return
-	}
-
-	if company == nil {
-		utils.NotFoundResponse(c, "Company not found")
-		return
-	}
-
-	// Convert to DTO
-	companyDTO := convertCompanyToDTO(company)
-
-	utils.SuccessResponse(c, http.StatusOK, companyDTO)
+	utils.HandleUpdate(c, models.UpdateCompany, convertCompanyToDTO, prepareCompanyUpdate, "company")
 }
 
 // DeleteCompany handles DELETE /companies/:id
@@ -196,22 +107,7 @@ func (h *CompanyHandler) UpdateCompany(c *gin.Context) {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/companies/{id} [delete]
 func (h *CompanyHandler) DeleteCompany(c *gin.Context) {
-	// Parse ID from URL
-	idStr := c.Param("id")
-	id, err := ulid.Parse(idStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid company ID format")
-		return
-	}
-
-	// Delete company from the database
-	err = models.DeleteCompany(c.Request.Context(), types.FromULID(id))
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error deleting company: "+err.Error())
-		return
-	}
-
-	utils.SuccessResponse(c, http.StatusNoContent, nil)
+	utils.HandleDelete(c, models.DeleteCompany, "company")
 }
 
 // Helper functions for DTO conversion
@@ -242,3 +138,32 @@ func convertUpdateCompanyDTOToModel(dto dto.CompanyUpdateDto, id types.ULID) mod
 
 	return update
 }
+
+// prepareCompanyUpdate prepares the company update object by parsing the ID, binding the JSON, and converting the DTO to a model
+func prepareCompanyUpdate(c *gin.Context) (models.CompanyUpdate, error) {
+	// Parse ID from URL
+	id, err := utils.ParseID(c, "id")
+	if err != nil {
+		responses.BadRequestResponse(c, "Invalid company ID format")
+		return models.CompanyUpdate{}, err
+	}
+
+	// Parse request body
+	var companyUpdateDTO dto.CompanyUpdateDto
+	if err := utils.BindJSON(c, &companyUpdateDTO); err != nil {
+		responses.BadRequestResponse(c, err.Error())
+		return models.CompanyUpdate{}, err
+	}
+
+	// Convert DTO to model
+	return convertUpdateCompanyDTOToModel(companyUpdateDTO, id), nil
+}
+
+// createCompanyWrapper is a wrapper function for models.CreateCompany that takes a DTO as input
+func createCompanyWrapper(ctx context.Context, createDTO dto.CompanyCreateDto) (*models.Company, error) {
+	// Convert DTO to model
+	companyCreate := convertCreateCompanyDTOToModel(createDTO)
+
+	// Call the original function
+	return models.CreateCompany(ctx, companyCreate)
+}

backend/internal/api/handlers/customer_handler.go

@@ -1,14 +1,15 @@
 package handlers
 
 import (
+	"context"
 	"fmt"
 	"net/http"
 
 	"github.com/gin-gonic/gin"
-	"github.com/oklog/ulid/v2"
+	"github.com/timetracker/backend/internal/api/dto"
 	"github.com/timetracker/backend/internal/api/middleware"
+	"github.com/timetracker/backend/internal/api/responses"
 	"github.com/timetracker/backend/internal/api/utils"
-	dto "github.com/timetracker/backend/internal/dtos"
 	"github.com/timetracker/backend/internal/models"
 	"github.com/timetracker/backend/internal/types"
 )
@@ -34,20 +35,7 @@ func NewCustomerHandler() *CustomerHandler {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/customers [get]
 func (h *CustomerHandler) GetCustomers(c *gin.Context) {
-	// Get customers from the database
-	customers, err := models.GetAllCustomers(c.Request.Context())
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving customers: "+err.Error())
-		return
-	}
-
-	// Convert to DTOs
-	customerDTOs := make([]dto.CustomerDto, len(customers))
-	for i, customer := range customers {
-		customerDTOs[i] = convertCustomerToDTO(&customer)
-	}
-
-	utils.SuccessResponse(c, http.StatusOK, customerDTOs)
+	utils.HandleGetAll(c, models.GetAllCustomers, convertCustomerToDTO, "customers")
 }
 
 // GetCustomerByID handles GET /customers/:id
@@ -66,30 +54,7 @@ func (h *CustomerHandler) GetCustomers(c *gin.Context) {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/customers/{id} [get]
 func (h *CustomerHandler) GetCustomerByID(c *gin.Context) {
-	// Parse ID from URL
-	idStr := c.Param("id")
-	id, err := ulid.Parse(idStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid customer ID format")
-		return
-	}
-
-	// Get customer from the database
-	customer, err := models.GetCustomerByID(c.Request.Context(), types.FromULID(id))
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving customer: "+err.Error())
-		return
-	}
-
-	if customer == nil {
-		utils.NotFoundResponse(c, "Customer not found")
-		return
-	}
-
-	// Convert to DTO
-	customerDTO := convertCustomerToDTO(customer)
-
-	utils.SuccessResponse(c, http.StatusOK, customerDTO)
+	utils.HandleGetByID(c, models.GetCustomerByID, convertCustomerToDTO, "customer")
 }
 
 // GetCustomersByCompanyID handles GET /customers/company/:companyId
@@ -111,24 +76,26 @@ func (h *CustomerHandler) GetCustomersByCompanyID(c *gin.Context) {
 	companyIDStr := c.Param("companyId")
 	companyID, err := parseCompanyID(companyIDStr)
 	if err != nil {
-		utils.BadRequestResponse(c, "Invalid company ID format")
+		responses.BadRequestResponse(c, "Invalid company ID format")
 		return
 	}
 
-	// Get customers from the database
-	customers, err := models.GetCustomersByCompanyID(c.Request.Context(), companyID)
+	// Create a wrapper function that takes a ULID but calls the original function with an int
+	getByCompanyIDFn := func(ctx context.Context, _ types.ULID) ([]models.Customer, error) {
+		return models.GetCustomersByCompanyID(ctx, companyID)
+	}
+
+	// Get customers from the database and convert to DTOs
+	customers, err := getByCompanyIDFn(c.Request.Context(), types.ULID{})
 	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving customers: "+err.Error())
+		responses.InternalErrorResponse(c, "Error retrieving customers: "+err.Error())
 		return
 	}
 
 	// Convert to DTOs
-	customerDTOs := make([]dto.CustomerDto, len(customers))
-	for i, customer := range customers {
-		customerDTOs[i] = convertCustomerToDTO(&customer)
-	}
+	customerDTOs := utils.ConvertToDTO(customers, convertCustomerToDTO)
 
-	utils.SuccessResponse(c, http.StatusOK, customerDTOs)
+	responses.SuccessResponse(c, http.StatusOK, customerDTOs)
 }
 
 // CreateCustomer handles POST /customers
@@ -146,37 +113,19 @@ func (h *CustomerHandler) GetCustomersByCompanyID(c *gin.Context) {
 //	@Failure		500			{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/customers [post]
 func (h *CustomerHandler) CreateCustomer(c *gin.Context) {
+	// We need to use a custom wrapper for CreateCustomer because we need to get the user ID from the context
 	userID, err := middleware.GetUserIDFromContext(c)
 	if err != nil {
-		utils.UnauthorizedResponse(c, "User not authenticated")
-		return
-	}
-	// Parse request body
-	var customerCreateDTO dto.CustomerCreateDto
-	if err := c.ShouldBindJSON(&customerCreateDTO); err != nil {
-		utils.BadRequestResponse(c, "Invalid request body: "+err.Error())
+		responses.UnauthorizedResponse(c, "User not authenticated")
 		return
 	}
 
-	// Convert DTO to model
-	customerCreate, err := convertCreateCustomerDTOToModel(customerCreateDTO)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid request body: "+err.Error())
-		return
-	}
-	customerCreate.OwnerUserID = &userID
-
-	// Create customer in the database
-	customer, err := models.CreateCustomer(c.Request.Context(), customerCreate)
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error creating customer: "+err.Error())
-		return
+	// Use a closure to capture the userID
+	createFn := func(ctx context.Context, createDTO dto.CustomerCreateDto) (*models.Customer, error) {
+		return createCustomerWrapper(ctx, createDTO, userID)
 	}
 
-	// Convert to DTO
-	customerDTO := convertCustomerToDTO(customer)
-
-	utils.SuccessResponse(c, http.StatusCreated, customerDTO)
+	utils.HandleCreate(c, createFn, convertCustomerToDTO, "customer")
 }
 
 // UpdateCustomer handles PUT /customers/:id
@@ -196,47 +145,7 @@ func (h *CustomerHandler) CreateCustomer(c *gin.Context) {
 //	@Failure		500			{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/customers/{id} [put]
 func (h *CustomerHandler) UpdateCustomer(c *gin.Context) {
-	// Parse ID from URL
-	idStr := c.Param("id")
-	id, err := ulid.Parse(idStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid customer ID format")
-		return
-	}
-
-	// Parse request body
-	var customerUpdateDTO dto.CustomerUpdateDto
-	if err := c.ShouldBindJSON(&customerUpdateDTO); err != nil {
-		utils.BadRequestResponse(c, "Invalid request body: "+err.Error())
-		return
-	}
-
-	// Set ID from URL
-	customerUpdateDTO.ID = id.String()
-
-	// Convert DTO to model
-	customerUpdate, err := convertUpdateCustomerDTOToModel(customerUpdateDTO)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid request body: "+err.Error())
-		return
-	}
-
-	// Update customer in the database
-	customer, err := models.UpdateCustomer(c.Request.Context(), customerUpdate)
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error updating customer: "+err.Error())
-		return
-	}
-
-	if customer == nil {
-		utils.NotFoundResponse(c, "Customer not found")
-		return
-	}
-
-	// Convert to DTO
-	customerDTO := convertCustomerToDTO(customer)
-
-	utils.SuccessResponse(c, http.StatusOK, customerDTO)
+	utils.HandleUpdate(c, models.UpdateCustomer, convertCustomerToDTO, prepareCustomerUpdate, "customer")
 }
 
 // DeleteCustomer handles DELETE /customers/:id
@@ -254,22 +163,7 @@ func (h *CustomerHandler) UpdateCustomer(c *gin.Context) {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/customers/{id} [delete]
 func (h *CustomerHandler) DeleteCustomer(c *gin.Context) {
-	// Parse ID from URL
-	idStr := c.Param("id")
-	id, err := ulid.Parse(idStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid customer ID format")
-		return
-	}
-
-	// Delete customer from the database
-	err = models.DeleteCustomer(c.Request.Context(), types.FromULID(id))
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error deleting customer: "+err.Error())
-		return
-	}
-
-	utils.SuccessResponse(c, http.StatusNoContent, nil)
+	utils.HandleDelete(c, models.DeleteCustomer, "customer")
 }
 
 // Helper functions for DTO conversion
@@ -338,3 +232,47 @@ func parseCompanyID(idStr string) (int, error) {
 	_, err := fmt.Sscanf(idStr, "%d", &id)
 	return id, err
 }
+
+// prepareCustomerUpdate prepares the customer update object by parsing the ID, binding the JSON, and converting the DTO to a model
+func prepareCustomerUpdate(c *gin.Context) (models.CustomerUpdate, error) {
+	// Parse ID from URL
+	id, err := utils.ParseID(c, "id")
+	if err != nil {
+		responses.BadRequestResponse(c, "Invalid customer ID format")
+		return models.CustomerUpdate{}, err
+	}
+
+	// Parse request body
+	var customerUpdateDTO dto.CustomerUpdateDto
+	if err := utils.BindJSON(c, &customerUpdateDTO); err != nil {
+		responses.BadRequestResponse(c, err.Error())
+		return models.CustomerUpdate{}, err
+	}
+
+	// Set ID from URL
+	customerUpdateDTO.ID = id.String()
+
+	// Convert DTO to model
+	customerUpdate, err := convertUpdateCustomerDTOToModel(customerUpdateDTO)
+	if err != nil {
+		responses.BadRequestResponse(c, "Invalid request body: "+err.Error())
+		return models.CustomerUpdate{}, err
+	}
+
+	return customerUpdate, nil
+}
+
+// createCustomerWrapper is a wrapper function for models.CreateCustomer that takes a DTO as input
+func createCustomerWrapper(ctx context.Context, createDTO dto.CustomerCreateDto, userID types.ULID) (*models.Customer, error) {
+	// Convert DTO to model
+	customerCreate, err := convertCreateCustomerDTOToModel(createDTO)
+	if err != nil {
+		return nil, err
+	}
+
+	// Set the owner user ID
+	customerCreate.OwnerUserID = &userID
+
+	// Call the original function
+	return models.CreateCustomer(ctx, customerCreate)
+}

backend/internal/api/handlers/project_handler.go

@@ -1,13 +1,13 @@
 package handlers
 
 import (
+	"context"
 	"fmt"
-	"net/http"
 
 	"github.com/gin-gonic/gin"
-	"github.com/oklog/ulid/v2"
+	"github.com/timetracker/backend/internal/api/dto"
+	"github.com/timetracker/backend/internal/api/responses"
 	"github.com/timetracker/backend/internal/api/utils"
-	dto "github.com/timetracker/backend/internal/dtos"
 	"github.com/timetracker/backend/internal/models"
 	"github.com/timetracker/backend/internal/types"
 )
@@ -33,20 +33,7 @@ func NewProjectHandler() *ProjectHandler {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/projects [get]
 func (h *ProjectHandler) GetProjects(c *gin.Context) {
-	// Get projects from the database
-	projects, err := models.GetAllProjects(c.Request.Context())
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving projects: "+err.Error())
-		return
-	}
-
-	// Convert to DTOs
-	projectDTOs := make([]dto.ProjectDto, len(projects))
-	for i, project := range projects {
-		projectDTOs[i] = convertProjectToDTO(&project)
-	}
-
-	utils.SuccessResponse(c, http.StatusOK, projectDTOs)
+	utils.HandleGetAll(c, models.GetAllProjects, convertProjectToDTO, "projects")
 }
 
 // GetProjectsWithCustomers handles GET /projects/with-customers
@@ -62,20 +49,7 @@ func (h *ProjectHandler) GetProjects(c *gin.Context) {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/projects/with-customers [get]
 func (h *ProjectHandler) GetProjectsWithCustomers(c *gin.Context) {
-	// Get projects with customers from the database
-	projects, err := models.GetAllProjectsWithCustomers(c.Request.Context())
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving projects: "+err.Error())
-		return
-	}
-
-	// Convert to DTOs
-	projectDTOs := make([]dto.ProjectDto, len(projects))
-	for i, project := range projects {
-		projectDTOs[i] = convertProjectToDTO(&project)
-	}
-
-	utils.SuccessResponse(c, http.StatusOK, projectDTOs)
+	utils.HandleGetAll(c, models.GetAllProjectsWithCustomers, convertProjectToDTO, "projects with customers")
 }
 
 // GetProjectByID handles GET /projects/:id
@@ -94,30 +68,7 @@ func (h *ProjectHandler) GetProjectsWithCustomers(c *gin.Context) {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/projects/{id} [get]
 func (h *ProjectHandler) GetProjectByID(c *gin.Context) {
-	// Parse ID from URL
-	idStr := c.Param("id")
-	id, err := ulid.Parse(idStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid project ID format")
-		return
-	}
-
-	// Get project from the database
-	project, err := models.GetProjectByID(c.Request.Context(), types.FromULID(id))
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving project: "+err.Error())
-		return
-	}
-
-	if project == nil {
-		utils.NotFoundResponse(c, "Project not found")
-		return
-	}
-
-	// Convert to DTO
-	projectDTO := convertProjectToDTO(project)
-
-	utils.SuccessResponse(c, http.StatusOK, projectDTO)
+	utils.HandleGetByID(c, models.GetProjectByID, convertProjectToDTO, "project")
 }
 
 // GetProjectsByCustomerID handles GET /projects/customer/:customerId
@@ -135,28 +86,7 @@ func (h *ProjectHandler) GetProjectByID(c *gin.Context) {
 //	@Failure		500			{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/projects/customer/{customerId} [get]
 func (h *ProjectHandler) GetProjectsByCustomerID(c *gin.Context) {
-	// Parse customer ID from URL
-	customerIDStr := c.Param("customerId")
-	customerID, err := ulid.Parse(customerIDStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid customer ID format")
-		return
-	}
-
-	// Get projects from the database
-	projects, err := models.GetProjectsByCustomerID(c.Request.Context(), customerID)
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving projects: "+err.Error())
-		return
-	}
-
-	// Convert to DTOs
-	projectDTOs := make([]dto.ProjectDto, len(projects))
-	for i, project := range projects {
-		projectDTOs[i] = convertProjectToDTO(&project)
-	}
-
-	utils.SuccessResponse(c, http.StatusOK, projectDTOs)
+	utils.HandleGetByFilter(c, models.GetProjectsByCustomerID, convertProjectToDTO, "projects", "customerId")
 }
 
 // CreateProject handles POST /projects
@@ -174,31 +104,7 @@ func (h *ProjectHandler) GetProjectsByCustomerID(c *gin.Context) {
 //	@Failure		500		{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/projects [post]
 func (h *ProjectHandler) CreateProject(c *gin.Context) {
-	// Parse request body
-	var projectCreateDTO dto.ProjectCreateDto
-	if err := c.ShouldBindJSON(&projectCreateDTO); err != nil {
-		utils.BadRequestResponse(c, "Invalid request body: "+err.Error())
-		return
-	}
-
-	// Convert DTO to model
-	projectCreate, err := convertCreateProjectDTOToModel(projectCreateDTO)
-	if err != nil {
-		utils.BadRequestResponse(c, err.Error())
-		return
-	}
-
-	// Create project in the database
-	project, err := models.CreateProject(c.Request.Context(), projectCreate)
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error creating project: "+err.Error())
-		return
-	}
-
-	// Convert to DTO
-	projectDTO := convertProjectToDTO(project)
-
-	utils.SuccessResponse(c, http.StatusCreated, projectDTO)
+	utils.HandleCreate(c, createProjectWrapper, convertProjectToDTO, "project")
 }
 
 // UpdateProject handles PUT /projects/:id
@@ -218,44 +124,7 @@ func (h *ProjectHandler) CreateProject(c *gin.Context) {
 //	@Failure		500		{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/projects/{id} [put]
 func (h *ProjectHandler) UpdateProject(c *gin.Context) {
-	// Parse ID from URL
-	idStr := c.Param("id")
-	id, err := types.ULIDFromString(idStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid project ID format")
-		return
-	}
-
-	// Parse request body
-	var projectUpdateDTO dto.ProjectUpdateDto
-	if err := c.ShouldBindJSON(&projectUpdateDTO); err != nil {
-		utils.BadRequestResponse(c, "Invalid request body: "+err.Error())
-		return
-	}
-
-	// Convert DTO to model
-	projectUpdate, err := convertUpdateProjectDTOToModel(projectUpdateDTO, id)
-	if err != nil {
-		utils.BadRequestResponse(c, err.Error())
-		return
-	}
-
-	// Update project in the database
-	project, err := models.UpdateProject(c.Request.Context(), projectUpdate)
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error updating project: "+err.Error())
-		return
-	}
-
-	if project == nil {
-		utils.NotFoundResponse(c, "Project not found")
-		return
-	}
-
-	// Convert to DTO
-	projectDTO := convertProjectToDTO(project)
-
-	utils.SuccessResponse(c, http.StatusOK, projectDTO)
+	utils.HandleUpdate(c, models.UpdateProject, convertProjectToDTO, prepareProjectUpdate, "project")
 }
 
 // DeleteProject handles DELETE /projects/:id
@@ -273,34 +142,23 @@ func (h *ProjectHandler) UpdateProject(c *gin.Context) {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/projects/{id} [delete]
 func (h *ProjectHandler) DeleteProject(c *gin.Context) {
-	// Parse ID from URL
-	idStr := c.Param("id")
-	id, err := ulid.Parse(idStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid project ID format")
-		return
-	}
-
-	// Delete project from the database
-	err = models.DeleteProject(c.Request.Context(), id)
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error deleting project: "+err.Error())
-		return
-	}
-
-	utils.SuccessResponse(c, http.StatusNoContent, nil)
+	utils.HandleDelete(c, models.DeleteProject, "project")
 }
 
 // Helper functions for DTO conversion
 
 func convertProjectToDTO(project *models.Project) dto.ProjectDto {
-	customerId := project.CustomerID.String()
+	var customerIdPtr *string
+	if project.CustomerID != nil {
+		customerIdStr := project.CustomerID.String()
+		customerIdPtr = &customerIdStr
+	}
 	return dto.ProjectDto{
 		ID:         project.ID.String(),
 		CreatedAt:  project.CreatedAt,
 		UpdatedAt:  project.UpdatedAt,
 		Name:       project.Name,
-		CustomerID: &customerId,
+		CustomerID: customerIdPtr,
 	}
 }
 
@@ -308,7 +166,6 @@ func convertCreateProjectDTOToModel(dto dto.ProjectCreateDto) (models.ProjectCre
 	create := models.ProjectCreate{Name: dto.Name}
 	// Convert CustomerID from int to ULID (this is a simplification, adjust as needed)
 	if dto.CustomerID != nil {
-
 		customerID, err := types.ULIDFromString(*dto.CustomerID)
 		if err != nil {
 			return models.ProjectCreate{}, fmt.Errorf("invalid customer ID: %w", err)
@@ -329,17 +186,53 @@ func convertUpdateProjectDTOToModel(dto dto.ProjectUpdateDto, id types.ULID) (mo
 
 	if dto.CustomerID.Valid {
 		if dto.CustomerID.Value == nil {
-			update.CustomerID = nil
-
+			update.CustomerID = types.Null[types.ULID]()
 		} else {
-			// Convert CustomerID from int to ULID (this is a simplification, adjust as needed)
 			customerID, err := types.ULIDFromString(*dto.CustomerID.Value)
 			if err != nil {
 				return models.ProjectUpdate{}, fmt.Errorf("invalid customer ID: %w", err)
 			}
-			update.CustomerID = &customerID
+			update.CustomerID = types.NewNullable(customerID)
 		}
 	}
 
 	return update, nil
 }
+
+// prepareProjectUpdate prepares the project update object by parsing the ID, binding the JSON, and converting the DTO to a model
+func prepareProjectUpdate(c *gin.Context) (models.ProjectUpdate, error) {
+	// Parse ID from URL
+	id, err := utils.ParseID(c, "id")
+	if err != nil {
+		responses.BadRequestResponse(c, "Invalid project ID format")
+		return models.ProjectUpdate{}, err
+	}
+
+	// Parse request body
+	var projectUpdateDTO dto.ProjectUpdateDto
+	if err := utils.BindJSON(c, &projectUpdateDTO); err != nil {
+		responses.BadRequestResponse(c, err.Error())
+		return models.ProjectUpdate{}, err
+	}
+
+	// Convert DTO to model
+	projectUpdate, err := convertUpdateProjectDTOToModel(projectUpdateDTO, id)
+	if err != nil {
+		responses.BadRequestResponse(c, err.Error())
+		return models.ProjectUpdate{}, err
+	}
+
+	return projectUpdate, nil
+}
+
+// createProjectWrapper is a wrapper function for models.CreateProject that takes a DTO as input
+func createProjectWrapper(ctx context.Context, createDTO dto.ProjectCreateDto) (*models.Project, error) {
+	// Convert DTO to model
+	projectCreate, err := convertCreateProjectDTOToModel(createDTO)
+	if err != nil {
+		return nil, err
+	}
+
+	// Call the original function
+	return models.CreateProject(ctx, projectCreate)
+}

backend/internal/api/handlers/timeentry_handler.go

@@ -1,15 +1,13 @@
 package handlers
 
 import (
+	"context"
 	"fmt"
-	"net/http"
-	"time"
 
 	"github.com/gin-gonic/gin"
-	"github.com/oklog/ulid/v2"
-	"github.com/timetracker/backend/internal/api/middleware"
+	"github.com/timetracker/backend/internal/api/dto"
+	"github.com/timetracker/backend/internal/api/responses"
 	"github.com/timetracker/backend/internal/api/utils"
-	dto "github.com/timetracker/backend/internal/dtos"
 	"github.com/timetracker/backend/internal/models"
 	"github.com/timetracker/backend/internal/types"
 )
@@ -35,20 +33,7 @@ func NewTimeEntryHandler() *TimeEntryHandler {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/time-entries [get]
 func (h *TimeEntryHandler) GetTimeEntries(c *gin.Context) {
-	// Get time entries from the database
-	timeEntries, err := models.GetAllTimeEntries(c.Request.Context())
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving time entries: "+err.Error())
-		return
-	}
-
-	// Convert to DTOs
-	timeEntryDTOs := make([]dto.TimeEntryDto, len(timeEntries))
-	for i, timeEntry := range timeEntries {
-		timeEntryDTOs[i] = convertTimeEntryToDTO(&timeEntry)
-	}
-
-	utils.SuccessResponse(c, http.StatusOK, timeEntryDTOs)
+	utils.HandleGetAll(c, models.GetAllTimeEntries, convertTimeEntryToDTO, "time entries")
 }
 
 // GetTimeEntryByID handles GET /time-entries/:id
@@ -67,30 +52,7 @@ func (h *TimeEntryHandler) GetTimeEntries(c *gin.Context) {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/time-entries/{id} [get]
 func (h *TimeEntryHandler) GetTimeEntryByID(c *gin.Context) {
-	// Parse ID from URL
-	idStr := c.Param("id")
-	id, err := ulid.Parse(idStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid time entry ID format")
-		return
-	}
-
-	// Get time entry from the database
-	timeEntry, err := models.GetTimeEntryByID(c.Request.Context(), types.FromULID(id))
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving time entry: "+err.Error())
-		return
-	}
-
-	if timeEntry == nil {
-		utils.NotFoundResponse(c, "Time entry not found")
-		return
-	}
-
-	// Convert to DTO
-	timeEntryDTO := convertTimeEntryToDTO(timeEntry)
-
-	utils.SuccessResponse(c, http.StatusOK, timeEntryDTO)
+	utils.HandleGetByID(c, models.GetTimeEntryByID, convertTimeEntryToDTO, "time entry")
 }
 
 // GetTimeEntriesByUserID handles GET /time-entries/user/:userId
@@ -108,28 +70,7 @@ func (h *TimeEntryHandler) GetTimeEntryByID(c *gin.Context) {
 //	@Failure		500		{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/time-entries/user/{userId} [get]
 func (h *TimeEntryHandler) GetTimeEntriesByUserID(c *gin.Context) {
-	// Parse user ID from URL
-	userIDStr := c.Param("userId")
-	userID, err := ulid.Parse(userIDStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid user ID format")
-		return
-	}
-
-	// Get time entries from the database
-	timeEntries, err := models.GetTimeEntriesByUserID(c.Request.Context(), types.FromULID(userID))
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving time entries: "+err.Error())
-		return
-	}
-
-	// Convert to DTOs
-	timeEntryDTOs := make([]dto.TimeEntryDto, len(timeEntries))
-	for i, timeEntry := range timeEntries {
-		timeEntryDTOs[i] = convertTimeEntryToDTO(&timeEntry)
-	}
-
-	utils.SuccessResponse(c, http.StatusOK, timeEntryDTOs)
+	utils.HandleGetByFilter(c, models.GetTimeEntriesByUserID, convertTimeEntryToDTO, "time entries", "userId")
 }
 
 // GetMyTimeEntries handles GET /time-entries/me
@@ -145,27 +86,7 @@ func (h *TimeEntryHandler) GetTimeEntriesByUserID(c *gin.Context) {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/time-entries/me [get]
 func (h *TimeEntryHandler) GetMyTimeEntries(c *gin.Context) {
-	// Get user ID from context (set by AuthMiddleware)
-	userID, err := middleware.GetUserIDFromContext(c)
-	if err != nil {
-		utils.UnauthorizedResponse(c, "User not authenticated")
-		return
-	}
-
-	// Get time entries from the database
-	timeEntries, err := models.GetTimeEntriesByUserID(c.Request.Context(), userID)
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving time entries: "+err.Error())
-		return
-	}
-
-	// Convert to DTOs
-	timeEntryDTOs := make([]dto.TimeEntryDto, len(timeEntries))
-	for i, timeEntry := range timeEntries {
-		timeEntryDTOs[i] = convertTimeEntryToDTO(&timeEntry)
-	}
-
-	utils.SuccessResponse(c, http.StatusOK, timeEntryDTOs)
+	utils.HandleGetByUserID(c, models.GetTimeEntriesByUserID, convertTimeEntryToDTO, "time entries")
 }
 
 // GetTimeEntriesByProjectID handles GET /time-entries/project/:projectId
@@ -183,28 +104,7 @@ func (h *TimeEntryHandler) GetMyTimeEntries(c *gin.Context) {
 //	@Failure		500			{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/time-entries/project/{projectId} [get]
 func (h *TimeEntryHandler) GetTimeEntriesByProjectID(c *gin.Context) {
-	// Parse project ID from URL
-	projectIDStr := c.Param("projectId")
-	projectID, err := ulid.Parse(projectIDStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid project ID format")
-		return
-	}
-
-	// Get time entries from the database
-	timeEntries, err := models.GetTimeEntriesByProjectID(c.Request.Context(), types.FromULID(projectID))
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving time entries: "+err.Error())
-		return
-	}
-
-	// Convert to DTOs
-	timeEntryDTOs := make([]dto.TimeEntryDto, len(timeEntries))
-	for i, timeEntry := range timeEntries {
-		timeEntryDTOs[i] = convertTimeEntryToDTO(&timeEntry)
-	}
-
-	utils.SuccessResponse(c, http.StatusOK, timeEntryDTOs)
+	utils.HandleGetByFilter(c, models.GetTimeEntriesByProjectID, convertTimeEntryToDTO, "time entries", "projectId")
 }
 
 // GetTimeEntriesByDateRange handles GET /time-entries/range
@@ -223,46 +123,7 @@ func (h *TimeEntryHandler) GetTimeEntriesByProjectID(c *gin.Context) {
 //	@Failure		500		{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/time-entries/range [get]
 func (h *TimeEntryHandler) GetTimeEntriesByDateRange(c *gin.Context) {
-	// Parse date range from query parameters
-	startStr := c.Query("start")
-	endStr := c.Query("end")
-
-	if startStr == "" || endStr == "" {
-		utils.BadRequestResponse(c, "Start and end dates are required")
-		return
-	}
-
-	start, err := time.Parse(time.RFC3339, startStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid start date format. Use ISO 8601 format (e.g., 2023-01-01T00:00:00Z)")
-		return
-	}
-
-	end, err := time.Parse(time.RFC3339, endStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid end date format. Use ISO 8601 format (e.g., 2023-01-01T00:00:00Z)")
-		return
-	}
-
-	if end.Before(start) {
-		utils.BadRequestResponse(c, "End date cannot be before start date")
-		return
-	}
-
-	// Get time entries from the database
-	timeEntries, err := models.GetTimeEntriesByDateRange(c.Request.Context(), start, end)
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving time entries: "+err.Error())
-		return
-	}
-
-	// Convert to DTOs
-	timeEntryDTOs := make([]dto.TimeEntryDto, len(timeEntries))
-	for i, timeEntry := range timeEntries {
-		timeEntryDTOs[i] = convertTimeEntryToDTO(&timeEntry)
-	}
-
-	utils.SuccessResponse(c, http.StatusOK, timeEntryDTOs)
+	utils.HandleGetByDateRange(c, models.GetTimeEntriesByDateRange, convertTimeEntryToDTO, "time entries")
 }
 
 // CreateTimeEntry handles POST /time-entries
@@ -280,31 +141,7 @@ func (h *TimeEntryHandler) GetTimeEntriesByDateRange(c *gin.Context) {
 //	@Failure		500			{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/time-entries [post]
 func (h *TimeEntryHandler) CreateTimeEntry(c *gin.Context) {
-	// Parse request body
-	var timeEntryCreateDTO dto.TimeEntryCreateDto
-	if err := c.ShouldBindJSON(&timeEntryCreateDTO); err != nil {
-		utils.BadRequestResponse(c, "Invalid request body: "+err.Error())
-		return
-	}
-
-	// Convert DTO to model
-	timeEntryCreate, err := convertCreateTimeEntryDTOToModel(timeEntryCreateDTO)
-	if err != nil {
-		utils.BadRequestResponse(c, err.Error())
-		return
-	}
-
-	// Create time entry in the database
-	timeEntry, err := models.CreateTimeEntry(c.Request.Context(), timeEntryCreate)
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error creating time entry: "+err.Error())
-		return
-	}
-
-	// Convert to DTO
-	timeEntryDTO := convertTimeEntryToDTO(timeEntry)
-
-	utils.SuccessResponse(c, http.StatusCreated, timeEntryDTO)
+	utils.HandleCreate(c, createTimeEntryWrapper, convertTimeEntryToDTO, "time entry")
 }
 
 // UpdateTimeEntry handles PUT /time-entries/:id
@@ -324,44 +161,7 @@ func (h *TimeEntryHandler) CreateTimeEntry(c *gin.Context) {
 //	@Failure		500			{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/time-entries/{id} [put]
 func (h *TimeEntryHandler) UpdateTimeEntry(c *gin.Context) {
-	// Parse ID from URL
-	idStr := c.Param("id")
-	id, err := types.ULIDFromString(idStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid time entry ID format")
-		return
-	}
-
-	// Parse request body
-	var timeEntryUpdateDTO dto.TimeEntryUpdateDto
-	if err := c.ShouldBindJSON(&timeEntryUpdateDTO); err != nil {
-		utils.BadRequestResponse(c, "Invalid request body: "+err.Error())
-		return
-	}
-
-	// Convert DTO to model
-	timeEntryUpdate, err := convertUpdateTimeEntryDTOToModel(timeEntryUpdateDTO, id)
-	if err != nil {
-		utils.BadRequestResponse(c, err.Error())
-		return
-	}
-
-	// Update time entry in the database
-	timeEntry, err := models.UpdateTimeEntry(c.Request.Context(), timeEntryUpdate)
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error updating time entry: "+err.Error())
-		return
-	}
-
-	if timeEntry == nil {
-		utils.NotFoundResponse(c, "Time entry not found")
-		return
-	}
-
-	// Convert to DTO
-	timeEntryDTO := convertTimeEntryToDTO(timeEntry)
-
-	utils.SuccessResponse(c, http.StatusOK, timeEntryDTO)
+	utils.HandleUpdate(c, models.UpdateTimeEntry, convertTimeEntryToDTO, prepareTimeEntryUpdate, "time entry")
 }
 
 // DeleteTimeEntry handles DELETE /time-entries/:id
@@ -379,22 +179,7 @@ func (h *TimeEntryHandler) UpdateTimeEntry(c *gin.Context) {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/time-entries/{id} [delete]
 func (h *TimeEntryHandler) DeleteTimeEntry(c *gin.Context) {
-	// Parse ID from URL
-	idStr := c.Param("id")
-	id, err := ulid.Parse(idStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid time entry ID format")
-		return
-	}
-
-	// Delete time entry from the database
-	err = models.DeleteTimeEntry(c.Request.Context(), types.FromULID(id))
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error deleting time entry: "+err.Error())
-		return
-	}
-
-	utils.SuccessResponse(c, http.StatusNoContent, nil)
+	utils.HandleDelete(c, models.DeleteTimeEntry, "time entry")
 }
 
 // Helper functions for DTO conversion
@@ -490,3 +275,42 @@ func convertUpdateTimeEntryDTOToModel(dto dto.TimeEntryUpdateDto, id types.ULID)
 
 	return update, nil
 }
+
+// prepareTimeEntryUpdate prepares the time entry update object by parsing the ID, binding the JSON, and converting the DTO to a model
+func prepareTimeEntryUpdate(c *gin.Context) (models.TimeEntryUpdate, error) {
+	// Parse ID from URL
+	idStr := c.Param("id")
+	id, err := types.ULIDFromString(idStr)
+	if err != nil {
+		responses.BadRequestResponse(c, "Invalid time entry ID format")
+		return models.TimeEntryUpdate{}, err
+	}
+
+	// Parse request body
+	var timeEntryUpdateDTO dto.TimeEntryUpdateDto
+	if err := utils.BindJSON(c, &timeEntryUpdateDTO); err != nil {
+		responses.BadRequestResponse(c, err.Error())
+		return models.TimeEntryUpdate{}, err
+	}
+
+	// Convert DTO to model
+	timeEntryUpdate, err := convertUpdateTimeEntryDTOToModel(timeEntryUpdateDTO, id)
+	if err != nil {
+		responses.BadRequestResponse(c, err.Error())
+		return models.TimeEntryUpdate{}, err
+	}
+
+	return timeEntryUpdate, nil
+}
+
+// createTimeEntryWrapper is a wrapper function for models.CreateTimeEntry that takes a DTO as input
+func createTimeEntryWrapper(ctx context.Context, createDTO dto.TimeEntryCreateDto) (*models.TimeEntry, error) {
+	// Convert DTO to model
+	timeEntryCreate, err := convertCreateTimeEntryDTOToModel(createDTO)
+	if err != nil {
+		return nil, err
+	}
+
+	// Call the original function
+	return models.CreateTimeEntry(ctx, timeEntryCreate)
+}

backend/internal/api/handlers/user_handler.go

@@ -1,13 +1,14 @@
 package handlers
 
 import (
+	"context"
 	"net/http"
 
 	"github.com/gin-gonic/gin"
-	"github.com/oklog/ulid/v2"
+	"github.com/timetracker/backend/internal/api/dto"
 	"github.com/timetracker/backend/internal/api/middleware"
+	"github.com/timetracker/backend/internal/api/responses"
 	"github.com/timetracker/backend/internal/api/utils"
-	dto "github.com/timetracker/backend/internal/dtos"
 	"github.com/timetracker/backend/internal/models"
 	"github.com/timetracker/backend/internal/types"
 )
@@ -33,20 +34,7 @@ func NewUserHandler() *UserHandler {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/users [get]
 func (h *UserHandler) GetUsers(c *gin.Context) {
-	// Get users from the database
-	users, err := models.GetAllUsers(c.Request.Context())
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving users: "+err.Error())
-		return
-	}
-
-	// Convert to DTOs
-	userDTOs := make([]dto.UserDto, len(users))
-	for i, user := range users {
-		userDTOs[i] = convertUserToDTO(&user)
-	}
-
-	utils.SuccessResponse(c, http.StatusOK, userDTOs)
+	utils.HandleGetAll(c, models.GetAllUsers, convertUserToDTO, "users")
 }
 
 // GetUserByID handles GET /users/:id
@@ -65,30 +53,29 @@ func (h *UserHandler) GetUsers(c *gin.Context) {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/users/{id} [get]
 func (h *UserHandler) GetUserByID(c *gin.Context) {
-	// Parse ID from URL
-	idStr := c.Param("id")
-	id, err := ulid.Parse(idStr)
+	// We need a custom wrapper for GetUserByID because the ID parameter is parsed differently
+	id, err := utils.ParseID(c, "id")
 	if err != nil {
-		utils.BadRequestResponse(c, "Invalid user ID format")
+		responses.BadRequestResponse(c, "Invalid user ID format")
 		return
 	}
 
 	// Get user from the database
-	user, err := models.GetUserByID(c.Request.Context(), types.FromULID(id))
+	user, err := models.GetUserByID(c.Request.Context(), id)
 	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving user: "+err.Error())
+		responses.InternalErrorResponse(c, "Error retrieving user: "+err.Error())
 		return
 	}
 
 	if user == nil {
-		utils.NotFoundResponse(c, "User not found")
+		responses.NotFoundResponse(c, "User not found")
 		return
 	}
 
 	// Convert to DTO
 	userDTO := convertUserToDTO(user)
 
-	utils.SuccessResponse(c, http.StatusOK, userDTO)
+	responses.SuccessResponse(c, http.StatusOK, userDTO)
 }
 
 // CreateUser handles POST /users
@@ -106,27 +93,7 @@ func (h *UserHandler) GetUserByID(c *gin.Context) {
 //	@Failure		500		{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/users [post]
 func (h *UserHandler) CreateUser(c *gin.Context) {
-	// Parse request body
-	var userCreateDTO dto.UserCreateDto
-	if err := c.ShouldBindJSON(&userCreateDTO); err != nil {
-		utils.BadRequestResponse(c, "Invalid request body: "+err.Error())
-		return
-	}
-
-	// Convert DTO to model
-	userCreate := convertCreateDTOToModel(userCreateDTO)
-
-	// Create user in the database
-	user, err := models.CreateUser(c.Request.Context(), userCreate)
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error creating user: "+err.Error())
-		return
-	}
-
-	// Convert to DTO
-	userDTO := convertUserToDTO(user)
-
-	utils.SuccessResponse(c, http.StatusCreated, userDTO)
+	utils.HandleCreate(c, createUserWrapper, convertUserToDTO, "user")
 }
 
 // UpdateUser handles PUT /users/:id
@@ -146,68 +113,7 @@ func (h *UserHandler) CreateUser(c *gin.Context) {
 //	@Failure		500		{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/users/{id} [put]
 func (h *UserHandler) UpdateUser(c *gin.Context) {
-	// Parse ID from URL
-	idStr := c.Param("id")
-	id, err := types.ULIDFromString(idStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid user ID format")
-		return
-	}
-
-	// Parse request body
-	var userUpdateDTO dto.UserUpdateDto
-	if err := c.ShouldBindJSON(&userUpdateDTO); err != nil {
-		utils.BadRequestResponse(c, "Invalid request body: "+err.Error())
-		return
-	}
-
-	// Convert DTO to Model
-	update := models.UserUpdate{
-		ID: id,
-	}
-
-	if userUpdateDTO.Email != nil {
-		update.Email = userUpdateDTO.Email
-	}
-	if userUpdateDTO.Password != nil {
-		update.Password = userUpdateDTO.Password
-	}
-	if userUpdateDTO.Role != nil {
-		update.Role = userUpdateDTO.Role
-	}
-
-	if userUpdateDTO.CompanyID.Valid {
-		if userUpdateDTO.CompanyID.Value != nil {
-			companyID, err := types.ULIDFromString(*userUpdateDTO.CompanyID.Value)
-			if err != nil {
-				utils.BadRequestResponse(c, "Invalid company ID format")
-				return
-			}
-			update.CompanyID = types.NewNullable(companyID)
-		} else {
-			update.CompanyID = types.Null[types.ULID]()
-		}
-	}
-
-	if userUpdateDTO.HourlyRate != nil {
-		update.HourlyRate = userUpdateDTO.HourlyRate
-	}
-	// Update user in the database
-	user, err := models.UpdateUser(c.Request.Context(), update)
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error updating user: "+err.Error())
-		return
-	}
-
-	if user == nil {
-		utils.NotFoundResponse(c, "User not found")
-		return
-	}
-
-	// Convert to DTO
-	userDTO := convertUserToDTO(user)
-
-	utils.SuccessResponse(c, http.StatusOK, userDTO)
+	utils.HandleUpdate(c, models.UpdateUser, convertUserToDTO, prepareUserUpdate, "user")
 }
 
 // DeleteUser handles DELETE /users/:id
@@ -225,22 +131,7 @@ func (h *UserHandler) UpdateUser(c *gin.Context) {
 //	@Failure		500	{object}	utils.Response{error=utils.ErrorInfo}
 //	@Router			/users/{id} [delete]
 func (h *UserHandler) DeleteUser(c *gin.Context) {
-	// Parse ID from URL
-	idStr := c.Param("id")
-	id, err := ulid.Parse(idStr)
-	if err != nil {
-		utils.BadRequestResponse(c, "Invalid user ID format")
-		return
-	}
-
-	// Delete user from the database
-	err = models.DeleteUser(c.Request.Context(), types.FromULID(id))
-	if err != nil {
-		utils.InternalErrorResponse(c, "Error deleting user: "+err.Error())
-		return
-	}
-
-	utils.SuccessResponse(c, http.StatusNoContent, nil)
+	utils.HandleDelete(c, models.DeleteUser, "user")
 }
 
 // Login handles POST /auth/login
@@ -260,21 +151,21 @@ func (h *UserHandler) Login(c *gin.Context) {
 	// Parse request body
 	var loginDTO dto.LoginDto
 	if err := c.ShouldBindJSON(&loginDTO); err != nil {
-		utils.BadRequestResponse(c, "Invalid request body: "+err.Error())
+		responses.BadRequestResponse(c, "Invalid request body: "+err.Error())
 		return
 	}
 
 	// Authenticate user
 	user, err := models.AuthenticateUser(c.Request.Context(), loginDTO.Email, loginDTO.Password)
 	if err != nil {
-		utils.UnauthorizedResponse(c, "Invalid login credentials")
+		responses.UnauthorizedResponse(c, "Invalid login credentials")
 		return
 	}
 
 	// Generate JWT token
 	token, err := middleware.GenerateToken(user, c)
 	if err != nil {
-		utils.InternalErrorResponse(c, "Error generating token: "+err.Error())
+		responses.InternalErrorResponse(c, "Error generating token: "+err.Error())
 		return
 	}
 
@@ -284,7 +175,7 @@ func (h *UserHandler) Login(c *gin.Context) {
 		User:  convertUserToDTO(user),
 	}
 
-	utils.SuccessResponse(c, http.StatusOK, tokenDTO)
+	responses.SuccessResponse(c, http.StatusOK, tokenDTO)
 }
 
 // Register handles POST /auth/register
@@ -303,7 +194,7 @@ func (h *UserHandler) Register(c *gin.Context) {
 	// Parse request body
 	var userCreateDTO dto.UserCreateDto
 	if err := c.ShouldBindJSON(&userCreateDTO); err != nil {
-		utils.BadRequestResponse(c, "Invalid request body: "+err.Error())
+		responses.BadRequestResponse(c, "Invalid request body: "+err.Error())
 		return
 	}
 
@@ -313,14 +204,14 @@ func (h *UserHandler) Register(c *gin.Context) {
 	// Create user in the database
 	user, err := models.CreateUser(c.Request.Context(), userCreate)
 	if err != nil {
-		utils.InternalErrorResponse(c, "Error creating user: "+err.Error())
+		responses.InternalErrorResponse(c, "Error creating user: "+err.Error())
 		return
 	}
 
 	// Generate JWT token
 	token, err := middleware.GenerateToken(user, c)
 	if err != nil {
-		utils.InternalErrorResponse(c, "Error generating token: "+err.Error())
+		responses.InternalErrorResponse(c, "Error generating token: "+err.Error())
 		return
 	}
 
@@ -330,7 +221,7 @@ func (h *UserHandler) Register(c *gin.Context) {
 		User:  convertUserToDTO(user),
 	}
 
-	utils.SuccessResponse(c, http.StatusCreated, tokenDTO)
+	responses.SuccessResponse(c, http.StatusCreated, tokenDTO)
 }
 
 // GetCurrentUser handles GET /auth/me
@@ -349,26 +240,26 @@ func (h *UserHandler) GetCurrentUser(c *gin.Context) {
 	// Get user ID from context (set by AuthMiddleware)
 	userID, err := middleware.GetUserIDFromContext(c)
 	if err != nil {
-		utils.UnauthorizedResponse(c, "User not authenticated")
+		responses.UnauthorizedResponse(c, "User not authenticated")
 		return
 	}
 
 	// Get user from the database
 	user, err := models.GetUserByID(c.Request.Context(), userID)
 	if err != nil {
-		utils.InternalErrorResponse(c, "Error retrieving user: "+err.Error())
+		responses.InternalErrorResponse(c, "Error retrieving user: "+err.Error())
 		return
 	}
 
 	if user == nil {
-		utils.NotFoundResponse(c, "User not found")
+		responses.NotFoundResponse(c, "User not found")
 		return
 	}
 
 	// Convert to DTO
 	userDTO := convertUserToDTO(user)
 
-	utils.SuccessResponse(c, http.StatusOK, userDTO)
+	responses.SuccessResponse(c, http.StatusOK, userDTO)
 }
 
 // Helper functions for DTO conversion
@@ -390,6 +281,58 @@ func convertUserToDTO(user *models.User) dto.UserDto {
 	}
 }
 
+// prepareUserUpdate prepares the user update object by parsing the ID, binding the JSON, and converting the DTO to a model
+func prepareUserUpdate(c *gin.Context) (models.UserUpdate, error) {
+	// Parse ID from URL
+	idStr := c.Param("id")
+	id, err := types.ULIDFromString(idStr)
+	if err != nil {
+		responses.BadRequestResponse(c, "Invalid user ID format")
+		return models.UserUpdate{}, err
+	}
+
+	// Parse request body
+	var userUpdateDTO dto.UserUpdateDto
+	if err := utils.BindJSON(c, &userUpdateDTO); err != nil {
+		responses.BadRequestResponse(c, err.Error())
+		return models.UserUpdate{}, err
+	}
+
+	// Convert DTO to Model
+	update := models.UserUpdate{
+		ID: id,
+	}
+
+	if userUpdateDTO.Email != nil {
+		update.Email = userUpdateDTO.Email
+	}
+	if userUpdateDTO.Password != nil {
+		update.Password = userUpdateDTO.Password
+	}
+	if userUpdateDTO.Role != nil {
+		update.Role = userUpdateDTO.Role
+	}
+
+	if userUpdateDTO.CompanyID.Valid {
+		if userUpdateDTO.CompanyID.Value != nil {
+			companyID, err := types.ULIDFromString(*userUpdateDTO.CompanyID.Value)
+			if err != nil {
+				responses.BadRequestResponse(c, "Invalid company ID format")
+				return models.UserUpdate{}, err
+			}
+			update.CompanyID = types.NewNullable(companyID)
+		} else {
+			update.CompanyID = types.Null[types.ULID]()
+		}
+	}
+
+	if userUpdateDTO.HourlyRate != nil {
+		update.HourlyRate = userUpdateDTO.HourlyRate
+	}
+
+	return update, nil
+}
+
 func convertCreateDTOToModel(dto dto.UserCreateDto) models.UserCreate {
 	var companyID *types.ULID
 	if dto.CompanyID != nil {
@@ -405,3 +348,12 @@ func convertCreateDTOToModel(dto dto.UserCreateDto) models.UserCreate {
 		HourlyRate: dto.HourlyRate,
 	}
 }
+
+// createUserWrapper is a wrapper function for models.CreateUser that takes a DTO as input
+func createUserWrapper(ctx context.Context, createDTO dto.UserCreateDto) (*models.User, error) {
+	// Convert DTO to model
+	userCreate := convertCreateDTOToModel(createDTO)
+
+	// Call the original function
+	return models.CreateUser(ctx, userCreate)
+}

backend/internal/api/middleware/api_key_middleware.go

@@ -2,7 +2,7 @@ package middleware
 
 import (
 	"github.com/gin-gonic/gin"
-	"github.com/timetracker/backend/internal/api/utils"
+	"github.com/timetracker/backend/internal/api/responses"
 	"github.com/timetracker/backend/internal/config"
 )
 
@@ -18,14 +18,14 @@ func APIKeyMiddleware(cfg *config.Config) gin.HandlerFunc {
 		// Get API key from header
 		apiKey := c.GetHeader("X-API-Key")
 		if apiKey == "" {
-			utils.UnauthorizedResponse(c, "API key is required")
+			responses.UnauthorizedResponse(c, "API key is required")
 			c.Abort()
 			return
 		}
 
 		// Validate API key
 		if apiKey != cfg.APIKey {
-			utils.UnauthorizedResponse(c, "Invalid API key")
+			responses.UnauthorizedResponse(c, "Invalid API key")
 			c.Abort()
 			return
 		}

backend/internal/api/middleware/jwt_auth.go

@@ -14,7 +14,7 @@ import (
 	"github.com/gin-gonic/gin"
 	"github.com/golang-jwt/jwt/v5"
 	"github.com/oklog/ulid/v2"
-	"github.com/timetracker/backend/internal/api/utils"
+	"github.com/timetracker/backend/internal/api/responses"
 	"github.com/timetracker/backend/internal/config"
 	"github.com/timetracker/backend/internal/models"
 	"github.com/timetracker/backend/internal/types"
@@ -73,7 +73,7 @@ func fileExists(path string) bool {
 }
 
 // generateRSAKeys generates RSA keys and saves them to disk
-func generateRSAKeys(cfg models.JWTConfig) error {
+func generateRSAKeys(cfg config.JWTConfig) error {
 	// Create key directory if it doesn't exist
 	if err := os.MkdirAll(cfg.KeyDir, 0700); err != nil {
 		return fmt.Errorf("failed to create key directory: %w", err)
@@ -167,7 +167,7 @@ type Claims struct {
 	UserID    string  `json:"userId"`
 	Email     string  `json:"email"`
 	Role      string  `json:"role"`
-	CompanyID string `json:"companyId"`
+	CompanyID *string `json:"companyId"`
 	jwt.RegisteredClaims
 }
 
@@ -177,14 +177,14 @@ func AuthMiddleware() gin.HandlerFunc {
 		// Get the token from cookie
 		tokenString, err := c.Cookie("jwt")
 		if err != nil {
-			utils.UnauthorizedResponse(c, "Authentication cookie is required")
+			responses.UnauthorizedResponse(c, "Authentication cookie is required")
 			c.Abort()
 			return
 		}
 
 		claims, err := validateToken(tokenString)
 		if err != nil {
-			utils.UnauthorizedResponse(c, "Invalid or expired token")
+			responses.UnauthorizedResponse(c, "Invalid or expired token")
 			c.Abort()
 			return
 		}
@@ -204,7 +204,7 @@ func RoleMiddleware(roles ...string) gin.HandlerFunc {
 	return func(c *gin.Context) {
 		userRole, exists := c.Get("role")
 		if !exists {
-			utils.UnauthorizedResponse(c, "User role not found in context")
+			responses.UnauthorizedResponse(c, "User role not found in context")
 			c.Abort()
 			return
 		}
@@ -212,7 +212,7 @@ func RoleMiddleware(roles ...string) gin.HandlerFunc {
 		// Check if the user's role is in the allowed roles
 		roleStr, ok := userRole.(string)
 		if !ok {
-			utils.InternalErrorResponse(c, "Invalid role type in context")
+			responses.InternalErrorResponse(c, "Invalid role type in context")
 			c.Abort()
 			return
 		}
@@ -226,7 +226,7 @@ func RoleMiddleware(roles ...string) gin.HandlerFunc {
 		}
 
 		if !allowed {
-			utils.ForbiddenResponse(c, "Insufficient permissions")
+			responses.ForbiddenResponse(c, "Insufficient permissions")
 			c.Abort()
 			return
 		}
@@ -238,11 +238,16 @@ func RoleMiddleware(roles ...string) gin.HandlerFunc {
 // GenerateToken creates a new JWT token for a user
 func GenerateToken(user *models.User, c *gin.Context) (string, error) {
 	// Create the claims
+	var companyId *string
+	if user.CompanyID != nil {
+		wrapper := user.CompanyID.String()
+		companyId = &wrapper
+	}
 	claims := Claims{
 		UserID:    user.ID.String(),
 		Email:     user.Email,
 		Role:      user.Role,
-		CompanyID: user.CompanyID.String(),
+		CompanyID: companyId,
 		RegisteredClaims: jwt.RegisteredClaims{
 			ExpiresAt: jwt.NewNumericDate(time.Now().Add(config.MustLoadConfig().JWTConfig.TokenDuration)),
 			IssuedAt:  jwt.NewNumericDate(time.Now()),

backend/internal/api/responses/response.go

@@ -1,4 +1,4 @@
-package utils
+package responses
 
 import (
 	"net/http"

backend/internal/api/utils/handler_utils.go

@@ -0,0 +1,286 @@
+package utils
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"github.com/timetracker/backend/internal/api/responses"
+	"github.com/timetracker/backend/internal/types"
+)
+
+// ParseID parses an ID from the URL parameter and converts it to a types.ULID
+func ParseID(c *gin.Context, paramName string) (types.ULID, error) {
+	idStr := c.Param(paramName)
+	return types.ULIDFromString(idStr)
+}
+
+// BindJSON binds the request body to the provided struct
+func BindJSON(c *gin.Context, obj interface{}) error {
+	if err := c.ShouldBindJSON(obj); err != nil {
+		return fmt.Errorf("invalid request body: %w", err)
+	}
+	return nil
+}
+
+// ConvertToDTO converts a slice of models to a slice of DTOs using the provided conversion function
+func ConvertToDTO[M any, D any](models []M, convertFn func(*M) D) []D {
+	dtos := make([]D, len(models))
+	for i, model := range models {
+		// Create a copy of the model to avoid issues with loop variable capture
+		modelCopy := model
+		dtos[i] = convertFn(&modelCopy)
+	}
+	return dtos
+}
+
+// HandleGetAll is a generic function to handle GET all entities endpoints
+func HandleGetAll[M any, D any](
+	c *gin.Context,
+	getAllFn func(ctx context.Context) ([]M, error),
+	convertFn func(*M) D,
+	entityName string,
+) {
+	// Get entities from the database
+	entities, err := getAllFn(c.Request.Context())
+	if err != nil {
+		responses.InternalErrorResponse(c, fmt.Sprintf("Error retrieving %s: %s", entityName, err.Error()))
+		return
+	}
+
+	// Convert to DTOs
+	dtos := ConvertToDTO(entities, convertFn)
+
+	responses.SuccessResponse(c, 200, dtos)
+}
+
+// HandleGetByID is a generic function to handle GET entity by ID endpoints
+func HandleGetByID[M any, D any](
+	c *gin.Context,
+	getByIDFn func(ctx context.Context, id types.ULID) (*M, error),
+	convertFn func(*M) D,
+	entityName string,
+) {
+	// Parse ID from URL
+	id, err := ParseID(c, "id")
+	if err != nil {
+		responses.BadRequestResponse(c, fmt.Sprintf("Invalid %s ID format", entityName))
+		return
+	}
+
+	// Get entity from the database
+	entity, err := getByIDFn(c.Request.Context(), id)
+	if err != nil {
+		responses.InternalErrorResponse(c, fmt.Sprintf("Error retrieving %s: %s", entityName, err.Error()))
+		return
+	}
+
+	if entity == nil {
+		responses.NotFoundResponse(c, fmt.Sprintf("%s not found", entityName))
+		return
+	}
+
+	// Convert to DTO
+	dto := convertFn(entity)
+
+	responses.SuccessResponse(c, 200, dto)
+}
+
+// HandleCreate is a generic function to handle POST entity endpoints
+func HandleCreate[C any, M any, D any](
+	c *gin.Context,
+	createFn func(ctx context.Context, create C) (*M, error),
+	convertFn func(*M) D,
+	entityName string,
+) {
+	// Parse request body
+	var createDTO C
+	if err := BindJSON(c, &createDTO); err != nil {
+		responses.BadRequestResponse(c, err.Error())
+		return
+	}
+
+	// Create entity in the database
+	entity, err := createFn(c.Request.Context(), createDTO)
+	if err != nil {
+		responses.InternalErrorResponse(c, fmt.Sprintf("Error creating %s: %s", entityName, err.Error()))
+		return
+	}
+
+	// Convert to DTO
+	dto := convertFn(entity)
+
+	responses.SuccessResponse(c, 201, dto)
+}
+
+// HandleDelete is a generic function to handle DELETE entity endpoints
+func HandleDelete(
+	c *gin.Context,
+	deleteFn func(ctx context.Context, id types.ULID) error,
+	entityName string,
+) {
+	// Parse ID from URL
+	id, err := ParseID(c, "id")
+	if err != nil {
+		responses.BadRequestResponse(c, fmt.Sprintf("Invalid %s ID format", entityName))
+		return
+	}
+
+	// Delete entity from the database
+	err = deleteFn(c.Request.Context(), id)
+	if err != nil {
+		responses.InternalErrorResponse(c, fmt.Sprintf("Error deleting %s: %s", entityName, err.Error()))
+		return
+	}
+
+	responses.SuccessResponse(c, 204, nil)
+}
+
+// HandleUpdate is a generic function to handle PUT entity endpoints
+// It takes a prepareUpdateFn that handles parsing the ID, binding the JSON, and converting the DTO to a model update object
+func HandleUpdate[U any, M any, D any](
+	c *gin.Context,
+	updateFn func(ctx context.Context, update U) (*M, error),
+	convertFn func(*M) D,
+	prepareUpdateFn func(*gin.Context) (U, error),
+	entityName string,
+) {
+	// Prepare the update object (parse ID, bind JSON, convert DTO to model)
+	update, err := prepareUpdateFn(c)
+	if err != nil {
+		// The prepareUpdateFn should handle setting the appropriate error response
+		return
+	}
+
+	// Update entity in the database
+	entity, err := updateFn(c.Request.Context(), update)
+	if err != nil {
+		responses.InternalErrorResponse(c, fmt.Sprintf("Error updating %s: %s", entityName, err.Error()))
+		return
+	}
+
+	if entity == nil {
+		responses.NotFoundResponse(c, fmt.Sprintf("%s not found", entityName))
+		return
+	}
+
+	// Convert to DTO
+	dto := convertFn(entity)
+
+	responses.SuccessResponse(c, http.StatusOK, dto)
+}
+
+// HandleGetByFilter is a generic function to handle GET entities by a filter parameter
+func HandleGetByFilter[M any, D any](
+	c *gin.Context,
+	getByFilterFn func(ctx context.Context, filterID types.ULID) ([]M, error),
+	convertFn func(*M) D,
+	entityName string,
+	paramName string,
+) {
+	// Parse filter ID from URL
+	filterID, err := ParseID(c, paramName)
+	if err != nil {
+		responses.BadRequestResponse(c, fmt.Sprintf("Invalid %s ID format", paramName))
+		return
+	}
+
+	// Get entities from the database
+	entities, err := getByFilterFn(c.Request.Context(), filterID)
+	if err != nil {
+		responses.InternalErrorResponse(c, fmt.Sprintf("Error retrieving %s: %s", entityName, err.Error()))
+		return
+	}
+
+	// Convert to DTOs
+	dtos := ConvertToDTO(entities, convertFn)
+
+	responses.SuccessResponse(c, http.StatusOK, dtos)
+}
+
+// HandleGetByUserID is a specialized function to handle GET entities by user ID
+func HandleGetByUserID[M any, D any](
+	c *gin.Context,
+	getByUserIDFn func(ctx context.Context, userID types.ULID) ([]M, error),
+	convertFn func(*M) D,
+	entityName string,
+) {
+	// Get user ID from context (set by AuthMiddleware)
+	userID, exists := c.Get("userID")
+	if !exists {
+		responses.UnauthorizedResponse(c, "User not authenticated")
+		return
+	}
+
+	userIDStr, ok := userID.(string)
+	if !ok {
+		responses.InternalErrorResponse(c, "Invalid user ID type in context")
+		return
+	}
+
+	parsedUserID, err := types.ULIDFromString(userIDStr)
+	if err != nil {
+		responses.InternalErrorResponse(c, fmt.Sprintf("Error parsing user ID: %s", err.Error()))
+		return
+	}
+
+	// Get entities from the database
+	entities, err := getByUserIDFn(c.Request.Context(), parsedUserID)
+	if err != nil {
+		responses.InternalErrorResponse(c, fmt.Sprintf("Error retrieving %s: %s", entityName, err.Error()))
+		return
+	}
+
+	// Convert to DTOs
+	dtos := ConvertToDTO(entities, convertFn)
+
+	responses.SuccessResponse(c, http.StatusOK, dtos)
+}
+
+// HandleGetByDateRange is a specialized function to handle GET entities by date range
+func HandleGetByDateRange[M any, D any](
+	c *gin.Context,
+	getByDateRangeFn func(ctx context.Context, start, end time.Time) ([]M, error),
+	convertFn func(*M) D,
+	entityName string,
+) {
+	// Parse date range from query parameters
+	startStr := c.Query("start")
+	endStr := c.Query("end")
+
+	if startStr == "" || endStr == "" {
+		responses.BadRequestResponse(c, "Start and end dates are required")
+		return
+	}
+
+	start, err := time.Parse(time.RFC3339, startStr)
+	if err != nil {
+		responses.BadRequestResponse(c, "Invalid start date format. Use ISO 8601 format (e.g., 2023-01-01T00:00:00Z)")
+		return
+	}
+
+	end, err := time.Parse(time.RFC3339, endStr)
+	if err != nil {
+		responses.BadRequestResponse(c, "Invalid end date format. Use ISO 8601 format (e.g., 2023-01-01T00:00:00Z)")
+		return
+	}
+
+	if end.Before(start) {
+		responses.BadRequestResponse(c, "End date cannot be before start date")
+		return
+	}
+
+	// Get entities from the database
+	entities, err := getByDateRangeFn(c.Request.Context(), start, end)
+	if err != nil {
+		responses.InternalErrorResponse(c, fmt.Sprintf("Error retrieving %s: %s", entityName, err.Error()))
+		return
+	}
+
+	// Convert to DTOs
+	dtos := ConvertToDTO(entities, convertFn)
+
+	responses.SuccessResponse(c, http.StatusOK, dtos)
+}

backend/internal/config/config.go

@@ -9,14 +9,54 @@ import (
 	"time"
 
 	"github.com/joho/godotenv"
-	"github.com/timetracker/backend/internal/models"
 	"gorm.io/gorm/logger"
 )
 
+// DatabaseConfig contains the configuration data for the database connection
+type DatabaseConfig struct {
+	Host         string
+	Port         int
+	User         string
+	Password     string
+	DBName       string
+	SSLMode      string
+	MaxIdleConns int           // Maximum number of idle connections
+	MaxOpenConns int           // Maximum number of open connections
+	MaxLifetime  time.Duration // Maximum lifetime of a connection
+	LogLevel     logger.LogLevel
+}
+
+// DefaultDatabaseConfig returns a default configuration with sensible values
+func DefaultDatabaseConfig() DatabaseConfig {
+	return DatabaseConfig{
+		Host:         "localhost",
+		Port:         5432,
+		User:         "timetracker",
+		Password:     "password",
+		DBName:       "timetracker",
+		SSLMode:      "disable",
+		MaxIdleConns: 10,
+		MaxOpenConns: 100,
+		MaxLifetime:  time.Hour,
+		LogLevel:     logger.Info,
+	}
+}
+
+// JWTConfig represents the configuration for JWT authentication
+type JWTConfig struct {
+	Secret        string
+	TokenDuration time.Duration
+	KeyGenerate   bool
+	KeyDir        string
+	PrivKeyFile   string
+	PubKeyFile    string
+	KeyBits       int
+}
+
 // Config represents the application configuration
 type Config struct {
-	Database  models.DatabaseConfig
-	JWTConfig models.JWTConfig
+	Database  DatabaseConfig
+	JWTConfig JWTConfig
 	APIKey    string
 }
 
@@ -26,8 +66,8 @@ func LoadConfig() (*Config, error) {
 	_ = godotenv.Load()
 
 	cfg := &Config{
-		Database:  models.DefaultDatabaseConfig(),
-		JWTConfig: models.JWTConfig{},
+		Database:  DefaultDatabaseConfig(),
+		JWTConfig: JWTConfig{},
 	}
 
 	// Load database configuration

backend/internal/db/db.go

@@ -0,0 +1,126 @@
+package db
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"log"
+	"time"
+
+	"github.com/timetracker/backend/internal/config"
+	"gorm.io/driver/postgres"
+	"gorm.io/gorm"
+	"gorm.io/gorm/logger"
+)
+
+// Global variable for the DB connection
+var db *gorm.DB
+
+// ErrDBNotInitialized is returned when a database operation is attempted before initialization
+var ErrDBNotInitialized = errors.New("database not initialized")
+
+// InitDB initializes the database connection (once at startup)
+// with the provided configuration
+func InitDB(config config.DatabaseConfig) error {
+	// Create connection using the default database name
+	gormDB, err := createConnection(config, config.DBName)
+	if err != nil {
+		return err
+	}
+
+	// Set the global db instance
+	db = gormDB
+
+	// Configure connection pool
+	return configureConnectionPool(db, config)
+}
+
+// GetEngine returns the DB instance with context
+func GetEngine(ctx context.Context) *gorm.DB {
+	if db == nil {
+		panic(ErrDBNotInitialized)
+	}
+	return db.WithContext(ctx)
+}
+
+// CloseDB closes the database connection
+func CloseDB() error {
+	if db == nil {
+		return nil
+	}
+
+	sqlDB, err := db.DB()
+	if err != nil {
+		return fmt.Errorf("error getting database connection: %w", err)
+	}
+
+	if err := sqlDB.Close(); err != nil {
+		return fmt.Errorf("error closing database connection: %w", err)
+	}
+
+	return nil
+}
+
+// GetGormDB is used for special cases like database creation
+func GetGormDB(dbConfig config.DatabaseConfig, dbName string) (*gorm.DB, error) {
+	return createConnection(dbConfig, dbName)
+}
+
+// MigrateDB performs database migrations for all models
+// This is a placeholder that will be called by models.MigrateDB
+func MigrateDB() error {
+	if db == nil {
+		return ErrDBNotInitialized
+	}
+	// The actual migration is implemented in models.MigrateDB
+	// This is just a placeholder to make the migrate/main.go file work
+	return errors.New("MigrateDB should be called from models package")
+}
+
+// createConnection creates a new database connection with the given configuration
+func createConnection(dbConfig config.DatabaseConfig, dbName string) (*gorm.DB, error) {
+	// Create DSN (Data Source Name)
+	dsn := fmt.Sprintf("host=%s port=%d user=%s password=%s dbname=%s sslmode=%s",
+		dbConfig.Host, dbConfig.Port, dbConfig.User, dbConfig.Password, dbName, dbConfig.SSLMode)
+
+	// Configure GORM logger
+	gormLogger := createGormLogger(dbConfig)
+
+	// Establish database connection with custom logger
+	gormDB, err := gorm.Open(postgres.Open(dsn), &gorm.Config{
+		Logger: gormLogger,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("error connecting to the database: %w", err)
+	}
+
+	return gormDB, nil
+}
+
+// createGormLogger creates a configured GORM logger instance
+func createGormLogger(dbConfig config.DatabaseConfig) logger.Interface {
+	return logger.New(
+		log.New(log.Writer(), "\r\n", log.LstdFlags), // io writer
+		logger.Config{
+			SlowThreshold:             200 * time.Millisecond, // Slow SQL threshold
+			LogLevel:                  dbConfig.LogLevel,      // Log level
+			IgnoreRecordNotFoundError: true,                   // Ignore ErrRecordNotFound error for logger
+			Colorful:                  true,                   // Enable color
+		},
+	)
+}
+
+// configureConnectionPool sets up the connection pool parameters
+func configureConnectionPool(db *gorm.DB, config config.DatabaseConfig) error {
+	sqlDB, err := db.DB()
+	if err != nil {
+		return fmt.Errorf("error getting database connection: %w", err)
+	}
+
+	// Set connection pool parameters
+	sqlDB.SetMaxIdleConns(config.MaxIdleConns)
+	sqlDB.SetMaxOpenConns(config.MaxOpenConns)
+	sqlDB.SetConnMaxLifetime(config.MaxLifetime)
+
+	return nil
+}

backend/internal/models/activity.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 
+	"github.com/timetracker/backend/internal/db"
 	"github.com/timetracker/backend/internal/types"
 	"gorm.io/gorm"
 )
@@ -36,7 +37,7 @@ type ActivityCreate struct {
 // GetActivityByID finds an Activity by its ID
 func GetActivityByID(ctx context.Context, id types.ULID) (*Activity, error) {
 	var activity Activity
-	result := GetEngine(ctx).Where("id = ?", id).First(&activity)
+	result := db.GetEngine(ctx).Where("id = ?", id).First(&activity)
 	if result.Error != nil {
 		if errors.Is(result.Error, gorm.ErrRecordNotFound) {
 			return nil, nil
@@ -49,7 +50,7 @@ func GetActivityByID(ctx context.Context, id types.ULID) (*Activity, error) {
 // GetAllActivities returns all Activities
 func GetAllActivities(ctx context.Context) ([]Activity, error) {
 	var activities []Activity
-	result := GetEngine(ctx).Find(&activities)
+	result := db.GetEngine(ctx).Find(&activities)
 	if result.Error != nil {
 		return nil, result.Error
 	}
@@ -63,7 +64,7 @@ func CreateActivity(ctx context.Context, create ActivityCreate) (*Activity, erro
 		BillingRate: create.BillingRate,
 	}
 
-	result := GetEngine(ctx).Create(&activity)
+	result := db.GetEngine(ctx).Create(&activity)
 	if result.Error != nil {
 		return nil, result.Error
 	}
@@ -91,6 +92,6 @@ func UpdateActivity(ctx context.Context, update ActivityUpdate) (*Activity, erro
 
 // DeleteActivity deletes an Activity by its ID
 func DeleteActivity(ctx context.Context, id types.ULID) error {
-	result := GetEngine(ctx).Delete(&Activity{}, id)
+	result := db.GetEngine(ctx).Delete(&Activity{}, id)
 	return result.Error
 }

backend/internal/models/company.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 
+	"github.com/timetracker/backend/internal/db"
 	"github.com/timetracker/backend/internal/types"
 	"gorm.io/gorm"
 )
@@ -33,7 +34,7 @@ type CompanyUpdate struct {
 // GetCompanyByID finds a company by its ID
 func GetCompanyByID(ctx context.Context, id types.ULID) (*Company, error) {
 	var company Company
-	result := GetEngine(ctx).Where("id = ?", id).First(&company)
+	result := db.GetEngine(ctx).Where("id = ?", id).First(&company)
 	if result.Error != nil {
 		if errors.Is(result.Error, gorm.ErrRecordNotFound) {
 			return nil, nil
@@ -46,7 +47,7 @@ func GetCompanyByID(ctx context.Context, id types.ULID) (*Company, error) {
 // GetAllCompanies returns all companies
 func GetAllCompanies(ctx context.Context) ([]Company, error) {
 	var companies []Company
-	result := GetEngine(ctx).Find(&companies)
+	result := db.GetEngine(ctx).Find(&companies)
 	if result.Error != nil {
 		return nil, result.Error
 	}
@@ -55,7 +56,7 @@ func GetAllCompanies(ctx context.Context) ([]Company, error) {
 
 func GetCustomersByCompanyID(ctx context.Context, companyID int) ([]Customer, error) {
 	var customers []Customer
-	result := GetEngine(ctx).Where("company_id = ?", companyID).Find(&customers)
+	result := db.GetEngine(ctx).Where("company_id = ?", companyID).Find(&customers)
 	if result.Error != nil {
 		return nil, result.Error
 	}
@@ -68,7 +69,7 @@ func CreateCompany(ctx context.Context, create CompanyCreate) (*Company, error)
 		Name: create.Name,
 	}
 
-	result := GetEngine(ctx).Create(&company)
+	result := db.GetEngine(ctx).Create(&company)
 	if result.Error != nil {
 		return nil, result.Error
 	}
@@ -96,6 +97,6 @@ func UpdateCompany(ctx context.Context, update CompanyUpdate) (*Company, error)
 
 // DeleteCompany deletes a company by its ID
 func DeleteCompany(ctx context.Context, id types.ULID) error {
-	result := GetEngine(ctx).Delete(&Company{}, id)
+	result := db.GetEngine(ctx).Delete(&Company{}, id)
 	return result.Error
 }

backend/internal/models/customer.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 
+	"github.com/timetracker/backend/internal/db"
 	"github.com/timetracker/backend/internal/types"
 	"gorm.io/gorm"
 )
@@ -39,7 +40,7 @@ type CustomerUpdate struct {
 // GetCustomerByID finds a customer by its ID
 func GetCustomerByID(ctx context.Context, id types.ULID) (*Customer, error) {
 	var customer Customer
-	result := GetEngine(ctx).Where("id = ?", id).First(&customer)
+	result := db.GetEngine(ctx).Where("id = ?", id).First(&customer)
 	if result.Error != nil {
 		if errors.Is(result.Error, gorm.ErrRecordNotFound) {
 			return nil, nil
@@ -52,7 +53,7 @@ func GetCustomerByID(ctx context.Context, id types.ULID) (*Customer, error) {
 // GetAllCustomers returns all customers
 func GetAllCustomers(ctx context.Context) ([]Customer, error) {
 	var customers []Customer
-	result := GetEngine(ctx).Find(&customers)
+	result := db.GetEngine(ctx).Find(&customers)
 	if result.Error != nil {
 		return nil, result.Error
 	}
@@ -66,7 +67,7 @@ func CreateCustomer(ctx context.Context, create CustomerCreate) (*Customer, erro
 		CompanyID: create.CompanyID,
 	}
 
-	result := GetEngine(ctx).Create(&customer)
+	result := db.GetEngine(ctx).Create(&customer)
 	if result.Error != nil {
 		return nil, result.Error
 	}
@@ -94,6 +95,6 @@ func UpdateCustomer(ctx context.Context, update CustomerUpdate) (*Customer, erro
 
 // DeleteCustomer deletes a customer by its ID
 func DeleteCustomer(ctx context.Context, id types.ULID) error {
-	result := GetEngine(ctx).Delete(&Customer{}, id)
+	result := db.GetEngine(ctx).Delete(&Customer{}, id)
 	return result.Error
 }

backend/internal/models/db.go

@@ -9,101 +9,33 @@ import (
 	"strings"
 	"time"
 
-	"gorm.io/driver/postgres" // For PostgreSQL
+	"github.com/timetracker/backend/internal/config"
+	"github.com/timetracker/backend/internal/db"
+	"github.com/timetracker/backend/internal/permissions"
+	"gorm.io/driver/postgres"
 	"gorm.io/gorm"
 	"gorm.io/gorm/logger"
 )
 
-// Global variable for the DB connection
-var defaultDB *gorm.DB
-
-// DatabaseConfig contains the configuration data for the database connection
-type DatabaseConfig struct {
-	Host         string
-	Port         int
-	User         string
-	Password     string
-	DBName       string
-	SSLMode      string
-	MaxIdleConns int           // Maximum number of idle connections
-	MaxOpenConns int           // Maximum number of open connections
-	MaxLifetime  time.Duration // Maximum lifetime of a connection
-	LogLevel     logger.LogLevel
-}
-
-// DefaultDatabaseConfig returns a default configuration with sensible values
-func DefaultDatabaseConfig() DatabaseConfig {
-	return DatabaseConfig{
-		Host:         "localhost",
-		Port:         5432,
-		User:         "timetracker",
-		Password:     "password",
-		DBName:       "timetracker",
-		SSLMode:      "disable",
-		MaxIdleConns: 10,
-		MaxOpenConns: 100,
-		MaxLifetime:  time.Hour,
-		LogLevel:     logger.Info,
-	}
-}
-
-// InitDB initializes the database connection (once at startup)
-// with the provided configuration
-func InitDB(config DatabaseConfig) error {
-	// Create DSN (Data Source Name)
-	dsn := fmt.Sprintf("host=%s port=%d user=%s password=%s dbname=%s sslmode=%s",
-		config.Host, config.Port, config.User, config.Password, config.DBName, config.SSLMode)
-
-	// Configure GORM logger
-	gormLogger := logger.New(
-		log.New(log.Writer(), "\r\n", log.LstdFlags), // io writer
-		logger.Config{
-			SlowThreshold:             200 * time.Millisecond, // Slow SQL threshold
-			LogLevel:                  config.LogLevel,        // Log level
-			IgnoreRecordNotFoundError: true,                   // Ignore ErrRecordNotFound error for logger
-			Colorful:                  true,                   // Enable color
-		},
-	)
-
-	// Establish database connection with custom logger
-	db, err := gorm.Open(postgres.Open(dsn), &gorm.Config{
-		Logger: gormLogger,
-	})
-	if err != nil {
-		return fmt.Errorf("error connecting to the database: %w", err)
-	}
-
-	// Configure connection pool
-	sqlDB, err := db.DB()
-	if err != nil {
-		return fmt.Errorf("error getting database connection: %w", err)
-	}
-
-	// Set connection pool parameters
-	sqlDB.SetMaxIdleConns(config.MaxIdleConns)
-	sqlDB.SetMaxOpenConns(config.MaxOpenConns)
-	sqlDB.SetConnMaxLifetime(config.MaxLifetime)
-
-	defaultDB = db
-	return nil
-}
-
 // MigrateDB performs database migrations for all models
 func MigrateDB() error {
-	if defaultDB == nil {
+	gormDB := db.GetEngine(context.Background())
+	if gormDB == nil {
 		return errors.New("database not initialized")
 	}
 
 	log.Println("Starting database migration...")
 
 	// Add all models that should be migrated here
-	err := defaultDB.AutoMigrate(
+	err := gormDB.AutoMigrate(
 		&Company{},
 		&User{},
 		&Customer{},
 		&Project{},
 		&Activity{},
 		&TimeEntry{},
+		&permissions.Role{},
+		&permissions.Policy{},
 	)
 
 	if err != nil {
@@ -114,34 +46,8 @@ func MigrateDB() error {
 	return nil
 }
 
-// GetEngine returns the DB instance, possibly with context
-func GetEngine(ctx context.Context) *gorm.DB {
-	if defaultDB == nil {
-		panic("database not initialized")
-	}
-	// If a special transaction is in ctx, you could check it here
-	return defaultDB.WithContext(ctx)
-}
-
-// CloseDB closes the database connection
-func CloseDB() error {
-	if defaultDB == nil {
-		return nil
-	}
-
-	sqlDB, err := defaultDB.DB()
-	if err != nil {
-		return fmt.Errorf("error getting database connection: %w", err)
-	}
-
-	if err := sqlDB.Close(); err != nil {
-		return fmt.Errorf("error closing database connection: %w", err)
-	}
-
-	return nil
-}
-
-func GetGormDB(dbConfig DatabaseConfig, dbName string) (*gorm.DB, error) {
+// GetGormDB is used for special cases like database creation
+func GetGormDB(dbConfig config.DatabaseConfig, dbName string) (*gorm.DB, error) {
 	dsn := fmt.Sprintf("host=%s port=%d user=%s password=%s dbname=%s sslmode=%s",
 		dbConfig.Host, dbConfig.Port, dbConfig.User, dbConfig.Password, dbName, dbConfig.SSLMode)
 
@@ -184,7 +90,7 @@ func UpdateModel(ctx context.Context, model any, updates any) error {
 	updateMap := make(map[string]any)
 
 	// Iterate through all fields
-	for i := 0; i < updateValue.NumField(); i++ {
+	for i := range updateValue.NumField() {
 		field := updateValue.Field(i)
 		fieldType := updateType.Field(i)
 
@@ -223,5 +129,14 @@ func UpdateModel(ctx context.Context, model any, updates any) error {
 		return nil // Nothing to update
 	}
 
-	return GetEngine(ctx).Model(model).Updates(updateMap).Error
+	return db.GetEngine(ctx).Model(model).Updates(updateMap).Error
+}
+
+// InitDB and CloseDB are forwarded to the db package for backward compatibility
+func InitDB(config config.DatabaseConfig) error {
+	return db.InitDB(config)
+}
+
+func CloseDB() error {
+	return db.CloseDB()
 }

backend/internal/models/jwt.go

@@ -1,13 +1,4 @@
 package models
 
-import "time"
-
-type JWTConfig struct {
-	Secret        string        `env:"JWT_SECRET" default:""`
-	TokenDuration time.Duration `env:"JWT_TOKEN_DURATION" default:"24h"`
-	KeyGenerate   bool          `env:"JWT_KEY_GENERATE" default:"true"`
-	KeyDir        string        `env:"JWT_KEY_DIR" default:"./keys"`
-	PrivKeyFile   string        `env:"JWT_PRIV_KEY_FILE" default:"jwt.key"`
-	PubKeyFile    string        `env:"JWT_PUB_KEY_FILE" default:"jwt.key.pub"`
-	KeyBits       int           `env:"JWT_KEY_BITS" default:"2048"`
-}
+// This file is intentionally left empty.
+// The JWTConfig struct has been moved to the config package.

backend/internal/models/project.go

@@ -5,7 +5,7 @@ import (
 	"errors"
 	"fmt"
 
-	"github.com/oklog/ulid/v2"
+	"github.com/timetracker/backend/internal/db"
 	"github.com/timetracker/backend/internal/types"
 	"gorm.io/gorm"
 )
@@ -14,7 +14,7 @@ import (
 type Project struct {
 	EntityBase
 	Name       string      `gorm:"column:name;not null"`
-	CustomerID *types.ULID `gorm:"column:customer_id;type:bytea;not null"`
+	CustomerID *types.ULID `gorm:"column:customer_id;type:bytea;index"`
 
 	// Relationships (for Eager Loading)
 	Customer *Customer `gorm:"foreignKey:CustomerID"`
@@ -35,7 +35,7 @@ type ProjectCreate struct {
 type ProjectUpdate struct {
 	ID         types.ULID                 `gorm:"-"` // Exclude from updates
 	Name       *string                    `gorm:"column:name"`
-	CustomerID *types.ULID `gorm:"column:customer_id"`
+	CustomerID types.Nullable[types.ULID] `gorm:"column:customer_id"`
 }
 
 // Validate checks if the Create struct contains valid data
@@ -44,7 +44,7 @@ func (pc *ProjectCreate) Validate() error {
 		return errors.New("project name cannot be empty")
 	}
 	// Check for valid CustomerID
-	if pc.CustomerID.Compare(types.ULID{}) == 0 {
+	if pc.CustomerID != nil && pc.CustomerID.Compare(types.ULID{}) == 0 {
 		return errors.New("customerID cannot be empty")
 	}
 	return nil
@@ -61,7 +61,7 @@ func (pu *ProjectUpdate) Validate() error {
 // GetProjectByID finds a project by its ID
 func GetProjectByID(ctx context.Context, id types.ULID) (*Project, error) {
 	var project Project
-	result := GetEngine(ctx).Where("id = ?", id).First(&project)
+	result := db.GetEngine(ctx).Where("id = ?", id).First(&project)
 	if result.Error != nil {
 		if errors.Is(result.Error, gorm.ErrRecordNotFound) {
 			return nil, nil
@@ -72,9 +72,9 @@ func GetProjectByID(ctx context.Context, id types.ULID) (*Project, error) {
 }
 
 // GetProjectWithCustomer loads a project with the associated customer information
-func GetProjectWithCustomer(ctx context.Context, id ulid.ULID) (*Project, error) {
+func GetProjectWithCustomer(ctx context.Context, id types.ULID) (*Project, error) {
 	var project Project
-	result := GetEngine(ctx).Preload("Customer").Where("id = ?", id).First(&project)
+	result := db.GetEngine(ctx).Preload("Customer").Where("id = ?", id).First(&project)
 	if result.Error != nil {
 		if errors.Is(result.Error, gorm.ErrRecordNotFound) {
 			return nil, nil
@@ -87,7 +87,7 @@ func GetProjectWithCustomer(ctx context.Context, id ulid.ULID) (*Project, error)
 // GetAllProjects returns all projects
 func GetAllProjects(ctx context.Context) ([]Project, error) {
 	var projects []Project
-	result := GetEngine(ctx).Find(&projects)
+	result := db.GetEngine(ctx).Find(&projects)
 	if result.Error != nil {
 		return nil, result.Error
 	}
@@ -97,7 +97,7 @@ func GetAllProjects(ctx context.Context) ([]Project, error) {
 // GetAllProjectsWithCustomers returns all projects with customer information
 func GetAllProjectsWithCustomers(ctx context.Context) ([]Project, error) {
 	var projects []Project
-	result := GetEngine(ctx).Preload("Customer").Find(&projects)
+	result := db.GetEngine(ctx).Preload("Customer").Find(&projects)
 	if result.Error != nil {
 		return nil, result.Error
 	}
@@ -105,9 +105,9 @@ func GetAllProjectsWithCustomers(ctx context.Context) ([]Project, error) {
 }
 
 // GetProjectsByCustomerID returns all projects of a specific customer
-func GetProjectsByCustomerID(ctx context.Context, customerID ulid.ULID) ([]Project, error) {
+func GetProjectsByCustomerID(ctx context.Context, customerId types.ULID) ([]Project, error) {
 	var projects []Project
-	result := GetEngine(ctx).Where("customer_id = ?", customerID).Find(&projects)
+	result := db.GetEngine(ctx).Where("customer_id = ?", customerId.ULID).Find(&projects)
 	if result.Error != nil {
 		return nil, result.Error
 	}
@@ -122,7 +122,7 @@ func CreateProject(ctx context.Context, create ProjectCreate) (*Project, error)
 	}
 
 	// Check if the customer exists
-	if create.CustomerID == nil {
+	if create.CustomerID != nil {
 		customer, err := GetCustomerByID(ctx, *create.CustomerID)
 		if err != nil {
 			return nil, fmt.Errorf("error checking the customer: %w", err)
@@ -137,7 +137,7 @@ func CreateProject(ctx context.Context, create ProjectCreate) (*Project, error)
 		CustomerID: create.CustomerID,
 	}
 
-	result := GetEngine(ctx).Create(&project)
+	result := db.GetEngine(ctx).Create(&project)
 	if result.Error != nil {
 		return nil, fmt.Errorf("error creating the project: %w", result.Error)
 	}
@@ -160,14 +160,19 @@ func UpdateProject(ctx context.Context, update ProjectUpdate) (*Project, error)
 	}
 
 	// If CustomerID is updated, check if the customer exists
-	if update.CustomerID != nil {
-		customer, err := GetCustomerByID(ctx, *update.CustomerID)
+	if update.CustomerID.Valid {
+		if update.CustomerID.Value != nil {
+			customer, err := GetCustomerByID(ctx, *update.CustomerID.Value)
 			if err != nil {
 				return nil, fmt.Errorf("error checking the customer: %w", err)
 			}
 			if customer == nil {
 				return nil, errors.New("the specified customer does not exist")
 			}
+		} else {
+			// If CustomerID is nil, set it to nil in the project
+			project.CustomerID = nil
+		}
 	}
 
 	// Use generic update function
@@ -180,9 +185,9 @@ func UpdateProject(ctx context.Context, update ProjectUpdate) (*Project, error)
 }
 
 // DeleteProject deletes a project by its ID
-func DeleteProject(ctx context.Context, id ulid.ULID) error {
+func DeleteProject(ctx context.Context, id types.ULID) error {
 	// Here you could check if dependent entities exist
-	result := GetEngine(ctx).Delete(&Project{}, id)
+	result := db.GetEngine(ctx).Delete(&Project{}, id)
 	if result.Error != nil {
 		return fmt.Errorf("error deleting the project: %w", result.Error)
 	}
@@ -199,7 +204,7 @@ func CreateProjectWithTransaction(ctx context.Context, create ProjectCreate) (*P
 	var project *Project
 
 	// Start transaction
-	err := GetEngine(ctx).Transaction(func(tx *gorm.DB) error {
+	err := db.GetEngine(ctx).Transaction(func(tx *gorm.DB) error {
 		// Customer check within the transaction
 		var customer Customer
 		if err := tx.Where("id = ?", create.CustomerID).First(&customer).Error; err != nil {

backend/internal/models/timeentry.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"time"
 
+	"github.com/timetracker/backend/internal/db"
 	"github.com/timetracker/backend/internal/types"
 	"gorm.io/gorm"
 )
@@ -105,7 +106,7 @@ func (tu *TimeEntryUpdate) Validate() error {
 // GetTimeEntryByID finds a time entry by its ID
 func GetTimeEntryByID(ctx context.Context, id types.ULID) (*TimeEntry, error) {
 	var timeEntry TimeEntry
-	result := GetEngine(ctx).Where("id = ?", id).First(&timeEntry)
+	result := db.GetEngine(ctx).Where("id = ?", id).First(&timeEntry)
 	if result.Error != nil {
 		if errors.Is(result.Error, gorm.ErrRecordNotFound) {
 			return nil, nil
@@ -118,7 +119,7 @@ func GetTimeEntryByID(ctx context.Context, id types.ULID) (*TimeEntry, error) {
 // GetTimeEntryWithRelations loads a time entry with all associated data
 func GetTimeEntryWithRelations(ctx context.Context, id types.ULID) (*TimeEntry, error) {
 	var timeEntry TimeEntry
-	result := GetEngine(ctx).
+	result := db.GetEngine(ctx).
 		Preload("User").
 		Preload("Project").
 		Preload("Project.Customer"). // Nested relationship
@@ -138,7 +139,7 @@ func GetTimeEntryWithRelations(ctx context.Context, id types.ULID) (*TimeEntry,
 // GetAllTimeEntries returns all time entries
 func GetAllTimeEntries(ctx context.Context) ([]TimeEntry, error) {
 	var timeEntries []TimeEntry
-	result := GetEngine(ctx).Find(&timeEntries)
+	result := db.GetEngine(ctx).Find(&timeEntries)
 	if result.Error != nil {
 		return nil, result.Error
 	}
@@ -148,7 +149,7 @@ func GetAllTimeEntries(ctx context.Context) ([]TimeEntry, error) {
 // GetTimeEntriesByUserID returns all time entries of a user
 func GetTimeEntriesByUserID(ctx context.Context, userID types.ULID) ([]TimeEntry, error) {
 	var timeEntries []TimeEntry
-	result := GetEngine(ctx).Where("user_id = ?", userID).Find(&timeEntries)
+	result := db.GetEngine(ctx).Where("user_id = ?", userID).Find(&timeEntries)
 	if result.Error != nil {
 		return nil, result.Error
 	}
@@ -158,7 +159,7 @@ func GetTimeEntriesByUserID(ctx context.Context, userID types.ULID) ([]TimeEntry
 // GetTimeEntriesByProjectID returns all time entries of a project
 func GetTimeEntriesByProjectID(ctx context.Context, projectID types.ULID) ([]TimeEntry, error) {
 	var timeEntries []TimeEntry
-	result := GetEngine(ctx).Where("project_id = ?", projectID).Find(&timeEntries)
+	result := db.GetEngine(ctx).Where("project_id = ?", projectID).Find(&timeEntries)
 	if result.Error != nil {
 		return nil, result.Error
 	}
@@ -169,7 +170,7 @@ func GetTimeEntriesByProjectID(ctx context.Context, projectID types.ULID) ([]Tim
 func GetTimeEntriesByDateRange(ctx context.Context, start, end time.Time) ([]TimeEntry, error) {
 	var timeEntries []TimeEntry
 	// Search for overlaps in the time range
-	result := GetEngine(ctx).
+	result := db.GetEngine(ctx).
 		Where("(start BETWEEN ? AND ?) OR (end BETWEEN ? AND ?)",
 			start, end, start, end).
 		Find(&timeEntries)
@@ -189,7 +190,7 @@ func SumBillableHoursByProject(ctx context.Context, projectID types.ULID) (float
 	var result Result
 
 	// SQL calculation of weighted hours
-	err := GetEngine(ctx).Raw(`
+	err := db.GetEngine(ctx).Raw(`
         SELECT SUM(
             EXTRACT(EPOCH FROM (end - start)) / 3600 * (billable / 100.0)
         ) as total_hours 
@@ -214,7 +215,7 @@ func CreateTimeEntry(ctx context.Context, create TimeEntryCreate) (*TimeEntry, e
 	// Start a transaction
 	var timeEntry *TimeEntry
 
-	err := GetEngine(ctx).Transaction(func(tx *gorm.DB) error {
+	err := db.GetEngine(ctx).Transaction(func(tx *gorm.DB) error {
 		// Check references
 		if err := validateReferences(tx, create.UserID, create.ProjectID, create.ActivityID); err != nil {
 			return err
@@ -295,7 +296,7 @@ func UpdateTimeEntry(ctx context.Context, update TimeEntryUpdate) (*TimeEntry, e
 	}
 
 	// Start a transaction for the update
-	err = GetEngine(ctx).Transaction(func(tx *gorm.DB) error {
+	err = db.GetEngine(ctx).Transaction(func(tx *gorm.DB) error {
 		// Check references if they are updated
 		if update.UserID != nil || update.ProjectID != nil || update.ActivityID != nil {
 			// Use current values if not updated
@@ -352,7 +353,7 @@ func UpdateTimeEntry(ctx context.Context, update TimeEntryUpdate) (*TimeEntry, e
 
 // DeleteTimeEntry deletes a time entry by its ID
 func DeleteTimeEntry(ctx context.Context, id types.ULID) error {
-	result := GetEngine(ctx).Delete(&TimeEntry{}, id)
+	result := db.GetEngine(ctx).Delete(&TimeEntry{}, id)
 	if result.Error != nil {
 		return fmt.Errorf("error deleting the time entry: %w", result.Error)
 	}

backend/internal/models/user.go

@@ -11,28 +11,12 @@ import (
 
 	"slices"
 
+	"github.com/timetracker/backend/internal/db"
 	"github.com/timetracker/backend/internal/types"
 	"golang.org/x/crypto/argon2"
 	"gorm.io/gorm"
 )
 
-// Argon2 Parameters
-const (
-	// Recommended values for Argon2id
-	ArgonTime    = 1
-	ArgonMemory  = 64 * 1024 // 64MB
-	ArgonThreads = 4
-	ArgonKeyLen  = 32
-	SaltLength   = 16
-)
-
-// Role Constants
-const (
-	RoleAdmin  = "admin"
-	RoleUser   = "user"
-	RoleViewer = "viewer"
-)
-
 // User represents a user in the system
 type User struct {
 	EntityBase
@@ -42,6 +26,7 @@ type User struct {
 	Role       string      `gorm:"column:role;not null;default:'user'"`
 	CompanyID  *types.ULID `gorm:"column:company_id;type:bytea;index"`
 	HourlyRate float64     `gorm:"column:hourly_rate;not null;default:0"`
+	Companies  []string    `gorm:"type:text[]"`
 
 	// Relationship for Eager Loading
 	Company *Company `gorm:"foreignKey:CompanyID"`
@@ -202,7 +187,7 @@ func (uc *UserCreate) Validate() error {
 		}
 	}
 
-	if uc.CompanyID.Compare(types.ULID{}) == 0 {
+	if uc.CompanyID != nil && uc.CompanyID.Compare(types.ULID{}) == 0 {
 		return errors.New("companyID cannot be empty")
 	}
 
@@ -290,7 +275,7 @@ func (uu *UserUpdate) Validate() error {
 // GetUserByID finds a user by their ID
 func GetUserByID(ctx context.Context, id types.ULID) (*User, error) {
 	var user User
-	result := GetEngine(ctx).Where("id = ?", id).First(&user)
+	result := db.GetEngine(ctx).Where("id = ?", id).First(&user)
 	if result.Error != nil {
 		if errors.Is(result.Error, gorm.ErrRecordNotFound) {
 			return nil, nil
@@ -303,7 +288,7 @@ func GetUserByID(ctx context.Context, id types.ULID) (*User, error) {
 // GetUserByEmail finds a user by their email
 func GetUserByEmail(ctx context.Context, email string) (*User, error) {
 	var user User
-	result := GetEngine(ctx).Where("email = ?", email).First(&user)
+	result := db.GetEngine(ctx).Where("email = ?", email).First(&user)
 	if result.Error != nil {
 		if errors.Is(result.Error, gorm.ErrRecordNotFound) {
 			return nil, nil
@@ -316,7 +301,7 @@ func GetUserByEmail(ctx context.Context, email string) (*User, error) {
 // GetUserWithCompany loads a user with their company
 func GetUserWithCompany(ctx context.Context, id types.ULID) (*User, error) {
 	var user User
-	result := GetEngine(ctx).Preload("Company").Where("id = ?", id).First(&user)
+	result := db.GetEngine(ctx).Preload("Company").Where("id = ?", id).First(&user)
 	if result.Error != nil {
 		if errors.Is(result.Error, gorm.ErrRecordNotFound) {
 			return nil, nil
@@ -329,7 +314,7 @@ func GetUserWithCompany(ctx context.Context, id types.ULID) (*User, error) {
 // GetAllUsers returns all users
 func GetAllUsers(ctx context.Context) ([]User, error) {
 	var users []User
-	result := GetEngine(ctx).Find(&users)
+	result := db.GetEngine(ctx).Find(&users)
 	if result.Error != nil {
 		return nil, result.Error
 	}
@@ -351,7 +336,7 @@ func GetUsersByCompanyID(ctx context.Context, companyID types.ULID) ([]User, err
 	var users []User
 	// Apply the dynamic company condition
 	condition := getCompanyCondition(&companyID)
-	result := GetEngine(ctx).Scopes(condition).Find(&users)
+	result := db.GetEngine(ctx).Scopes(condition).Find(&users)
 	if result.Error != nil {
 		return nil, result.Error
 	}
@@ -368,7 +353,7 @@ func CreateUser(ctx context.Context, create UserCreate) (*User, error) {
 	// Start a transaction
 	var user *User
 
-	err := GetEngine(ctx).Transaction(func(tx *gorm.DB) error {
+	err := db.GetEngine(ctx).Transaction(func(tx *gorm.DB) error {
 		// Check if email already exists
 		var count int64
 		if err := tx.Model(&User{}).Where("email = ?", create.Email).Count(&count).Error; err != nil {
@@ -378,6 +363,7 @@ func CreateUser(ctx context.Context, create UserCreate) (*User, error) {
 			return errors.New("email is already in use")
 		}
 
+		if create.CompanyID != nil {
 			// Check if company exists
 			var companyCount int64
 			if err := tx.Model(&Company{}).Where("id = ?", create.CompanyID).Count(&companyCount).Error; err != nil {
@@ -386,6 +372,7 @@ func CreateUser(ctx context.Context, create UserCreate) (*User, error) {
 			if companyCount == 0 {
 				return errors.New("the specified company does not exist")
 			}
+		}
 
 		// Hash password with unique salt
 		pwData, err := HashPassword(create.Password)
@@ -435,7 +422,7 @@ func UpdateUser(ctx context.Context, update UserUpdate) (*User, error) {
 	}
 
 	// Start a transaction for the update
-	err = GetEngine(ctx).Transaction(func(tx *gorm.DB) error {
+	err = db.GetEngine(ctx).Transaction(func(tx *gorm.DB) error {
 		// If email is updated, check if it's already in use
 		if update.Email != nil && *update.Email != user.Email {
 			var count int64
@@ -492,7 +479,6 @@ func UpdateUser(ctx context.Context, update UserUpdate) (*User, error) {
 			} else {
 				updates["company_id"] = *update.CompanyID.Value
 			}
-
 		}
 		if update.HourlyRate != nil {
 			updates["hourly_rate"] = *update.HourlyRate
@@ -521,7 +507,7 @@ func DeleteUser(ctx context.Context, id types.ULID) error {
 	// Here one could check if dependent entities exist
 	// e.g., don't delete if time entries still exist
 
-	result := GetEngine(ctx).Delete(&User{}, id)
+	result := db.GetEngine(ctx).Delete(&User{}, id)
 	if result.Error != nil {
 		return fmt.Errorf("error deleting user: %w", result.Error)
 	}
@@ -551,3 +537,20 @@ func AuthenticateUser(ctx context.Context, email, password string) (*User, error
 
 	return user, nil
 }
+
+// Argon2 Parameters
+const (
+	// Recommended values for Argon2id
+	ArgonTime    = 1
+	ArgonMemory  = 64 * 1024 // 64MB
+	ArgonThreads = 4
+	ArgonKeyLen  = 32
+	SaltLength   = 16
+)
+
+// Role Constants
+const (
+	RoleAdmin  = "admin"
+	RoleUser   = "user"
+	RoleViewer = "viewer"
+)

backend/internal/permissions/evaluator.go

@@ -0,0 +1,35 @@
+package permissions
+
+import (
+	"context"
+)
+
+func (u *User) EffectivePermissions(ctx context.Context, scope string) (Permission, error) {
+	if u.ActiveRole == nil {
+		return 0, nil
+	}
+
+	// Load the role and its associated policies using the helper function.
+	role, err := LoadRoleWithPolicies(ctx, u.ActiveRole.ID)
+	if err != nil {
+		return 0, err
+	}
+
+	var perm Permission
+	for _, policy := range role.Policies {
+		for pat, p := range policy.Scopes {
+			if MatchScope(pat, scope) {
+				perm |= p
+			}
+		}
+	}
+	return perm, nil
+}
+
+func (u *User) HasPermission(ctx context.Context, scope string, requiredPerm Permission) (bool, error) {
+	effective, err := u.EffectivePermissions(ctx, scope)
+	if err != nil {
+		return false, err
+	}
+	return (effective & requiredPerm) == requiredPerm, nil
+}

backend/internal/permissions/helpers.go

@@ -0,0 +1,23 @@
+package permissions
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/oklog/ulid/v2"
+	"github.com/timetracker/backend/internal/db"
+	"gorm.io/gorm"
+)
+
+// LoadRoleWithPolicies loads a role with its associated policies from the database.
+func LoadRoleWithPolicies(ctx context.Context, roleID ulid.ULID) (*Role, error) {
+	var role Role
+	err := db.GetEngine(ctx).Preload("Policies").First(&role, "id = ?", roleID).Error
+	if err != nil {
+		if err == gorm.ErrRecordNotFound {
+			return nil, fmt.Errorf("role with ID %s not found", roleID)
+		}
+		return nil, fmt.Errorf("failed to load role: %w", err)
+	}
+	return &role, nil
+}

backend/internal/permissions/matching.go

@@ -0,0 +1,11 @@
+package permissions
+
+import "strings"
+
+func MatchScope(pattern, scope string) bool {
+	if strings.HasSuffix(pattern, "/*") {
+		prefix := strings.TrimSuffix(pattern, "/*")
+		return strings.HasPrefix(scope, prefix)
+	}
+	return pattern == scope
+}

backend/internal/permissions/permissions.go

@@ -0,0 +1,13 @@
+package permissions
+
+type Permission uint64
+
+const (
+	PermRead Permission = 1 << iota // 1
+	PermWrite                       // 2
+	PermCreate                      // 4
+	PermList                        // 8
+	PermDelete                      // 16
+	PermModerate                    // 32
+	PermSuperadmin                  // 64
+)

backend/internal/permissions/policy.go

@@ -0,0 +1,40 @@
+package permissions
+
+import (
+	"database/sql/driver"
+	"encoding/json"
+	"errors"
+	"fmt"
+
+	"github.com/oklog/ulid/v2"
+)
+
+type Policy struct {
+	ID     ulid.ULID `gorm:"primaryKey;type:bytea"`
+	Name   string    `gorm:"not null"`
+	RoleID ulid.ULID `gorm:"type:bytea"`          //Fremdschlüssel
+	Scopes Scopes    `gorm:"type:jsonb;not null"` // JSONB-Spalte
+}
+
+// Scopes type to handle JSON marshalling
+type Scopes map[string]Permission
+
+// Scan scan value into Jsonb, implements sql.Scanner interface
+func (j *Scopes) Scan(value interface{}) error {
+	bytes, ok := value.([]byte)
+	if !ok {
+		return errors.New(fmt.Sprint("Failed to unmarshal JSONB value:", value))
+	}
+
+	var scopes map[string]Permission
+	if err := json.Unmarshal(bytes, &scopes); err != nil {
+		return err
+	}
+	*j = scopes
+	return nil
+}
+
+// Value return json value, implement driver.Valuer interface
+func (j Scopes) Value() (driver.Value, error) {
+	return json.Marshal(j)
+}

backend/internal/permissions/role.go

@@ -0,0 +1,11 @@
+package permissions
+
+import (
+	"github.com/oklog/ulid/v2"
+)
+
+type Role struct {
+	ID       ulid.ULID `gorm:"primaryKey;type:bytea"`
+	Name     string    `gorm:"unique;not null"`
+	Policies []Policy  `gorm:"foreignKey:RoleID"`
+}

backend/internal/permissions/user.go

@@ -0,0 +1,10 @@
+package permissions
+
+import (
+	"github.com/oklog/ulid/v2"
+)
+
+type User struct {
+	ActiveRole *Role     `gorm:"foreignKey:UserID"` // Beziehung zur aktiven Rolle
+	UserID     ulid.ULID `gorm:"type:bytea"`        //Fremdschlüssel
+}

backend/postman/activity.postman_collection.json

@@ -0,0 +1,168 @@
+{
+    "info": {
+        "_postman_id": "YOUR_POSTMAN_ID",
+        "name": "Activity API",
+        "schema": "https://schema.getpostman.com/json/collection/v2.1.0/collection.json"
+    },
+    "item": [
+        {
+            "name": "GET /api/activities",
+            "request": {
+                "method": "GET",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/activities",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "activities"
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "GET /api/activities/:id",
+            "request": {
+                "method": "GET",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/activities/:id",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "activities",
+                        ":id"
+                    ],
+                    "variable": [
+                        {
+                            "key": "id",
+                            "value": ""
+                        }
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "POST /api/activities",
+            "request": {
+                "method": "POST",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "body": {
+                    "mode": "raw",
+                    "raw": "{\n\t\"name\": \"\",\n\t\"billingRate\": 0\n}",
+                    "options": {
+                        "raw": {
+                            "language": "json"
+                        }
+                    }
+                },
+                "url": {
+                    "raw": "{{API_URL}}/api/activities",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "activities"
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "PUT /api/activities/:id",
+            "request": {
+                "method": "PUT",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "body": {
+                    "mode": "raw",
+                    "raw": "{\n\t\"name\": \"\",\n\t\"billingRate\": 0\n}",
+                    "options": {
+                        "raw": {
+                            "language": "json"
+                        }
+                    }
+                },
+                "url": {
+                    "raw": "{{API_URL}}/api/activities/:id",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "activities",
+                        ":id"
+                    ],
+                    "variable": [
+                        {
+                            "key": "id",
+                            "value": ""
+                        }
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "DELETE /api/activities/:id",
+            "request": {
+                "method": "DELETE",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/activities/:id",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "activities",
+                        ":id"
+                    ],
+                    "variable": [
+                        {
+                            "key": "id",
+                            "value": ""
+                        }
+                    ]
+                }
+            },
+            "response": []
+        }
+    ]
+}

backend/postman/company.postman_collection.json

@@ -0,0 +1,168 @@
+{
+    "info": {
+        "_postman_id": "YOUR_POSTMAN_ID",
+        "name": "Company API",
+        "schema": "https://schema.getpostman.com/json/collection/v2.1.0/collection.json"
+    },
+    "item": [
+        {
+            "name": "GET /api/companies",
+            "request": {
+                "method": "GET",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/companies",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "companies"
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "GET /api/companies/:id",
+            "request": {
+                "method": "GET",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/companies/:id",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "companies",
+                        ":id"
+                    ],
+                    "variable": [
+                        {
+                            "key": "id",
+                            "value": ""
+                        }
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "POST /api/companies",
+            "request": {
+                "method": "POST",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "body": {
+                    "mode": "raw",
+                    "raw": "{\n\t\"name\": \"\"\n}",
+                    "options": {
+                        "raw": {
+                            "language": "json"
+                        }
+                    }
+                },
+                "url": {
+                    "raw": "{{API_URL}}/api/companies",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "companies"
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "PUT /api/companies/:id",
+            "request": {
+                "method": "PUT",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "body": {
+                    "mode": "raw",
+                    "raw": "{\n\t\"name\": \"\"\n}",
+                    "options": {
+                        "raw": {
+                            "language": "json"
+                        }
+                    }
+                },
+                "url": {
+                    "raw": "{{API_URL}}/api/companies/:id",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "companies",
+                        ":id"
+                    ],
+                    "variable": [
+                        {
+                            "key": "id",
+                            "value": ""
+                        }
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "DELETE /api/companies/:id",
+            "request": {
+                "method": "DELETE",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/companies/:id",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "companies",
+                        ":id"
+                    ],
+                    "variable": [
+                        {
+                            "key": "id",
+                            "value": ""
+                        }
+                    ]
+                }
+            },
+            "response": []
+        }
+    ]
+}

backend/postman/customer.postman_collection.json

@@ -0,0 +1,200 @@
+{
+    "info": {
+        "_postman_id": "YOUR_POSTMAN_ID",
+        "name": "Customer API",
+        "schema": "https://schema.getpostman.com/json/collection/v2.1.0/collection.json"
+    },
+    "item": [
+        {
+            "name": "GET /api/customers",
+            "request": {
+                "method": "GET",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/customers",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "customers"
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "GET /api/customers/:id",
+            "request": {
+                "method": "GET",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/customers/:id",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "customers",
+                        ":id"
+                    ],
+                    "variable": [
+                        {
+                            "key": "id",
+                            "value": ""
+                        }
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "GET /api/customers/company/:companyId",
+            "request": {
+                "method": "GET",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/customers/company/:companyId",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "customers",
+                        "company",
+                        ":companyId"
+                    ],
+                    "variable": [
+                        {
+                            "key": "companyId",
+                            "value": ""
+                        }
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "POST /api/customers",
+            "request": {
+                "method": "POST",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "body": {
+                    "mode": "raw",
+                    "raw": "{\n\t\"name\": \"\",\n\t\"companyId\": \"\",\n\t\"ownerUserID\": \"\"\n}",
+                    "options": {
+                        "raw": {
+                            "language": "json"
+                        }
+                    }
+                },
+                "url": {
+                    "raw": "{{API_URL}}/api/customers",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "customers"
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "PUT /api/customers/:id",
+            "request": {
+                "method": "PUT",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "body": {
+                    "mode": "raw",
+                    "raw": "{\n\t\"name\": \"\",\n\t\"companyId\": \"\",\n\t\"ownerUserID\": \"\"\n}",
+                    "options": {
+                        "raw": {
+                            "language": "json"
+                        }
+                    }
+                },
+                "url": {
+                    "raw": "{{API_URL}}/api/customers/:id",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "customers",
+                        ":id"
+                    ],
+                    "variable": [
+                        {
+                            "key": "id",
+                            "value": ""
+                        }
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "DELETE /api/customers/:id",
+            "request": {
+                "method": "DELETE",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/customers/:id",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "customers",
+                        ":id"
+                    ],
+                    "variable": [
+                        {
+                            "key": "id",
+                            "value": ""
+                        }
+                    ]
+                }
+            },
+            "response": []
+        }
+    ]
+}

backend/postman/project.postman_collection.json

@@ -0,0 +1,225 @@
+{
+    "info": {
+        "_postman_id": "YOUR_POSTMAN_ID",
+        "name": "Project API",
+        "schema": "https://schema.getpostman.com/json/collection/v2.1.0/collection.json"
+    },
+    "item": [
+        {
+            "name": "GET /api/projects",
+            "request": {
+                "method": "GET",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/projects",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "projects"
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "GET /api/projects/with-customers",
+            "request": {
+                "method": "GET",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/projects/with-customers",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "projects",
+                        "with-customers"
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "GET /api/projects/:id",
+            "request": {
+                "method": "GET",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/projects/:id",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "projects",
+                        ":id"
+                    ],
+                    "variable": [
+                        {
+                            "key": "id",
+                            "value": ""
+                        }
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "GET /api/projects/customer/:customerId",
+            "request": {
+                "method": "GET",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/projects/customer/:customerId",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "projects",
+                        "customer",
+                        ":customerId"
+                    ],
+                    "variable": [
+                        {
+                            "key": "customerId",
+                            "value": ""
+                        }
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "POST /api/projects",
+            "request": {
+                "method": "POST",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "body": {
+                    "mode": "raw",
+                    "raw": "{\n\t\"name\": \"\",\n\t\"customerId\": \"\"\n}",
+                    "options": {
+                        "raw": {
+                            "language": "json"
+                        }
+                    }
+                },
+                "url": {
+                    "raw": "{{API_URL}}/api/projects",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "projects"
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "PUT /api/projects/:id",
+            "request": {
+                "method": "PUT",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "body": {
+                    "mode": "raw",
+                    "raw": "{\n\t\"name\": \"\",\n\t\"customerId\": \"\"\n}",
+                    "options": {
+                        "raw": {
+                            "language": "json"
+                        }
+                    }
+                },
+                "url": {
+                    "raw": "{{API_URL}}/api/projects/:id",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "projects",
+                        ":id"
+                    ],
+                    "variable": [
+                        {
+                            "key": "id",
+                            "value": ""
+                        }
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "DELETE /api/projects/:id",
+            "request": {
+                "method": "DELETE",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/projects/:id",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "projects",
+                        ":id"
+                    ],
+                    "variable": [
+                        {
+                            "key": "id",
+                            "value": ""
+                        }
+                    ]
+                }
+            },
+            "response": []
+        }
+    ]
+}

backend/postman/timeentry.postman_collection.json

@@ -0,0 +1,292 @@
+{
+    "info": {
+        "_postman_id": "YOUR_POSTMAN_ID",
+        "name": "TimeEntry API",
+        "schema": "https://schema.getpostman.com/json/collection/v2.1.0/collection.json"
+    },
+    "item": [
+        {
+            "name": "GET /api/time-entries",
+            "request": {
+                "method": "GET",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/time-entries",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "time-entries"
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "GET /api/time-entries/me",
+            "request": {
+                "method": "GET",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/time-entries/me",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "time-entries",
+                        "me"
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "GET /api/time-entries/range",
+            "request": {
+                "method": "GET",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/time-entries/range?start=2023-01-01T00:00:00Z&end=2023-01-02T00:00:00Z",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "time-entries",
+                        "range"
+                    ],
+                    "query": [
+                        {
+                            "key": "start",
+                            "value": "2023-01-01T00:00:00Z"
+                        },
+                        {
+                            "key": "end",
+                            "value": "2023-01-02T00:00:00Z"
+                        }
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "GET /api/time-entries/:id",
+            "request": {
+                "method": "GET",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/time-entries/:id",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "time-entries",
+                        ":id"
+                    ],
+                    "variable": [
+                        {
+                            "key": "id",
+                            "value": ""
+                        }
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "GET /api/time-entries/user/:userId",
+            "request": {
+                "method": "GET",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/time-entries/user/:userId",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "time-entries",
+                        "user",
+                        ":userId"
+                    ],
+                    "variable": [
+                        {
+                            "key": "userId",
+                            "value": ""
+                        }
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "GET /api/time-entries/project/:projectId",
+            "request": {
+                "method": "GET",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/time-entries/project/:projectId",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "time-entries",
+                        "project",
+                        ":projectId"
+                    ],
+                    "variable": [
+                        {
+                            "key": "projectId",
+                            "value": ""
+                        }
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "POST /api/time-entries",
+            "request": {
+                "method": "POST",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "body": {
+                    "mode": "raw",
+                    "raw": "{\n    \"userID\": \"\",\n    \"projectID\": \"\",\n    \"activityID\": \"\",\n    \"start\": \"2023-01-01T00:00:00Z\",\n    \"end\": \"2023-01-01T01:00:00Z\",\n    \"description\": \"\",\n    \"billable\": true\n}",
+                    "options": {
+                        "raw": {
+                            "language": "json"
+                        }
+                    }
+                },
+                "url": {
+                    "raw": "{{API_URL}}/api/time-entries",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "time-entries"
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "PUT /api/time-entries/:id",
+            "request": {
+                "method": "PUT",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "body": {
+                    "mode": "raw",
+                    "raw": "{\n    \"userID\": \"\",\n    \"projectID\": \"\",\n    \"activityID\": \"\",\n    \"start\": \"2023-01-01T00:00:00Z\",\n    \"end\": \"2023-01-01T01:00:00Z\",\n    \"description\": \"\",\n    \"billable\": true\n}",
+                    "options": {
+                        "raw": {
+                            "language": "json"
+                        }
+                    }
+                },
+                "url": {
+                    "raw": "{{API_URL}}/api/time-entries/:id",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "time-entries",
+                        ":id"
+                    ],
+                    "variable": [
+                        {
+                            "key": "id",
+                            "value": ""
+                        }
+                    ]
+                }
+            },
+            "response": []
+        },
+        {
+            "name": "DELETE /api/time-entries/:id",
+            "request": {
+                "method": "DELETE",
+                "header": [
+                    {
+                        "key": "Authorization",
+                        "value": "Bearer {{JWT_TOKEN}}",
+                        "type": "text"
+                    }
+                ],
+                "url": {
+                    "raw": "{{API_URL}}/api/time-entries/:id",
+                    "host": [
+                        "{{API_URL}}"
+                    ],
+                    "path": [
+                        "api",
+                        "time-entries",
+                        ":id"
+                    ],
+                    "variable": [
+                        {
+                            "key": "id",
+                            "value": ""
+                        }
+                    ]
+                }
+            },
+            "response": []
+        }
+    ]
+}

backend/postman/user.postman_collection.json

@@ -0,0 +1,241 @@
+{
+    "info": {
+        "_postman_id": "YOUR_POSTMAN_ID",
+        "name": "User API",
+        "schema": "https://schema.getpostman.com/json/collection/v2.1.0/collection.json"
+    },
+    "item": [
+        {
+            "name": "Auth",
+            "item": [
+                {
+                    "name": "POST /api/auth/login",
+                    "request": {
+                        "method": "POST",
+                        "header": [],
+                        "body": {
+                            "mode": "raw",
+                            "raw": "{\n\t\"email\": \"\",\n\t\"password\": \"\"\n}",
+                            "options": {
+                                "raw": {
+                                    "language": "json"
+                                }
+                            }
+                        },
+                        "url": {
+                            "raw": "{{API_URL}}/api/auth/login",
+                            "host": [
+                                "{{API_URL}}"
+                            ],
+                            "path": [
+                                "api",
+                                "auth",
+                                "login"
+                            ]
+                        }
+                    },
+                    "response": []
+                },
+                {
+                    "name": "POST /api/auth/register",
+                    "request": {
+                        "method": "POST",
+                        "header": [],
+                        "body": {
+                            "mode": "raw",
+                            "raw": "{\n\t\"email\": \"\",\n\t\"password\": \"\",\n\t\"role\": \"user\",\n\t\"companyID\": \"\",\n\t\"hourlyRate\": 0\n}",
+                            "options": {
+                                "raw": {
+                                    "language": "json"
+                                }
+                            }
+                        },
+                        "url": {
+                            "raw": "{{API_URL}}/api/auth/register",
+                            "host": [
+                                "{{API_URL}}"
+                            ],
+                            "path": [
+                                "api",
+                                "auth",
+                                "register"
+                            ]
+                        }
+                    },
+                    "response": []
+                },
+                {
+                    "name": "GET /api/auth/me",
+                    "request": {
+                        "method": "GET",
+                        "header": [
+                            {
+                                "key": "Authorization",
+                                "value": "Bearer {{JWT_TOKEN}}",
+                                "type": "text"
+                            }
+                        ],
+                        "url": {
+                            "raw": "{{API_URL}}/api/auth/me",
+                            "host": [
+                                "{{API_URL}}"
+                            ],
+                            "path": [
+                                "api",
+                                "auth",
+                                "me"
+                            ]
+                        }
+                    },
+                    "response": []
+                }
+            ]
+        },
+        {
+            "name": "Users",
+            "item": [
+                {
+                    "name": "GET /api/users",
+                    "request": {
+                        "method": "GET",
+                        "header": [
+                            {
+                                "key": "Authorization",
+                                "value": "Bearer {{JWT_TOKEN}}",
+                                "type": "text"
+                            }
+                        ],
+                        "url": {
+                            "raw": "{{API_URL}}/api/users",
+                            "host": [
+                                "{{API_URL}}"
+                            ],
+                            "path": [
+                                "api",
+                                "users"
+                            ]
+                        }
+                    },
+                    "response": []
+                },
+                {
+                    "name": "GET /api/users/:id",
+                    "request": {
+                        "method": "GET",
+                        "header": [
+                            {
+                                "key": "Authorization",
+                                "value": "Bearer {{JWT_TOKEN}}",
+                                "type": "text"
+                            }
+                        ],
+                        "url": {
+                            "raw": "{{API_URL}}/api/users/:id",
+                            "host": [
+                                "{{API_URL}}"
+                            ],
+                            "path": [
+                                "api",
+                                "users",
+                                ":id"
+                            ]
+                        }
+                    },
+                    "response": []
+                },
+                {
+                    "name": "POST /api/users",
+                    "request": {
+                        "method": "POST",
+                        "header": [
+                            {
+                                "key": "Authorization",
+                                "value": "Bearer {{JWT_TOKEN}}",
+                                "type": "text"
+                            }
+                        ],
+                        "body": {
+                            "mode": "raw",
+                            "raw": "{\n\t\"email\": \"\",\n\t\"password\": \"\",\n\t\"role\": \"user\",\n\t\"companyID\": \"\",\n\t\"hourlyRate\": 0\n}",
+                            "options": {
+                                "raw": {
+                                    "language": "json"
+                                }
+                            }
+                        },
+                        "url": {
+                            "raw": "{{API_URL}}/api/users",
+                            "host": [
+                                "{{API_URL}}"
+                            ],
+                            "path": [
+                                "api",
+                                "users"
+                            ]
+                        }
+                    },
+                    "response": []
+                },
+                {
+                    "name": "PUT /api/users/:id",
+                    "request": {
+                        "method": "PUT",
+                        "header": [
+                            {
+                                "key": "Authorization",
+                                "value": "Bearer {{JWT_TOKEN}}",
+                                "type": "text"
+                            }
+                        ],
+                        "body": {
+                            "mode": "raw",
+                            "raw": "{\n\t\"email\": \"\",\n\t\"password\": \"\",\n\t\"role\": \"user\",\n\t\"companyID\": \"\",\n\t\"hourlyRate\": 0\n}",
+                            "options": {
+                                "raw": {
+                                    "language": "json"
+                                }
+                            }
+                        },
+                        "url": {
+                            "raw": "{{API_URL}}/api/users/:id",
+                            "host": [
+                                "{{API_URL}}"
+                            ],
+                            "path": [
+                                "api",
+                                "users",
+                                ":id"
+                            ]
+                        }
+                    },
+                    "response": []
+                },
+                {
+                    "name": "DELETE /api/users/:id",
+                    "request": {
+                        "method": "DELETE",
+                        "header": [
+                            {
+                                "key": "Authorization",
+                                "value": "Bearer {{JWT_TOKEN}}",
+                                "type": "text"
+                            }
+                        ],
+                        "url": {
+                            "raw": "{{API_URL}}/api/users/:id",
+                            "host": [
+                                "{{API_URL}}"
+                            ],
+                            "path": [
+                                "api",
+                                "users",
+                                ":id"
+                            ]
+                        }
+                    },
+                    "response": []
+                }
+            ]
+        }
+    ]
+}

backend/tygo.yaml

@@ -1,5 +1,5 @@
 packages:
-  - path: github.com/timetracker/backend/internal/dtos
+  - path: "github.com/timetracker/backend/internal/api/dto"
     type_mappings:
       "time.Time": "string"
       "types.ULID": "string"

docu/permissions_plan.md

@@ -0,0 +1,250 @@
+# Berechtigungssystem Plan
+
+Dieser Plan beschreibt die Implementierung eines scope-basierten Berechtigungssystems für das TimeTracker-Projekt.
+
+## Grundkonzept
+
+- Ein **Benutzer** kann eine **Rolle** annehmen, aber immer nur eine ist aktiv.
+- Eine **Rolle** besteht aus mehreren **Policies**.
+- Eine **Policy** hat einen Namen und eine Map, die **Scopes** (z. B. `items/books`) einem **Berechtigungsschlüssel** (Bitflag) zuordnet.
+- Berechtigungsschlüssel sind Bitflags, die Permissions wie `read`, `write`, `create`, `list`, `delete`, `moderate`, `superadmin` usw. repräsentieren.
+- Scopes können **Wildcards** enthalten, z. B. `items/*`, das auf `items/books` vererbt wird.
+- Ziel: Berechtigungen sowohl im Go-Backend (für API-Sicherheit) als auch im TypeScript-Frontend (für UI-Anpassung) evaluieren.
+
+## Implementierung im Go-Backend
+
+### 1. Ordnerstruktur
+
+- Neuer Ordner: `backend/internal/permissions`
+- Dateien:
+    - `permissions.go`: `Permission`-Konstanten (Bitflags).
+    - `policy.go`: `Policy`-Struktur.
+    - `role.go`: `Role`-Struktur.
+    - `user.go`: Erweiterung der `User`-Struktur.
+    - `matching.go`: `matchScope`-Funktion.
+    - `evaluator.go`: `EffectivePermissions`- und `HasPermission`-Funktionen.
+
+### 2. Go-Strukturen
+
+- `permissions.go`:
+
+```go
+package permissions
+
+type Permission uint64
+
+const (
+    PermRead Permission = 1 << iota // 1
+    PermWrite                       // 2
+    PermCreate                      // 4
+    PermList                        // 8
+    PermDelete                      // 16
+    PermModerate                    // 32
+    PermSuperadmin                  // 64
+)
+```
+
+- `policy.go`:
+
+```go
+package permissions
+
+type Policy struct {
+    Name   string
+    Scopes map[string]Permission
+}
+```
+
+- `role.go`:
+
+```go
+package permissions
+
+type Role struct {
+    Name     string
+    Policies []Policy
+}
+```
+
+- `user.go`:
+
+```go
+package permissions
+
+import "github.com/your-org/your-project/backend/internal/models" // Pfad anpassen
+
+type User struct {
+    models.User // Einbettung
+    ActiveRole *Role
+}
+```
+
+### 3. Funktionen
+
+- `matching.go`:
+
+```go
+package permissions
+
+import "strings"
+
+func MatchScope(pattern, scope string) bool {
+    if strings.HasSuffix(pattern, "/*") {
+        prefix := strings.TrimSuffix(pattern, "/*")
+        return strings.HasPrefix(scope, prefix)
+    }
+    return pattern == scope
+}
+```
+
+- `evaluator.go`:
+
+```go
+package permissions
+
+func (u *User) EffectivePermissions(scope string) Permission {
+    if u.ActiveRole == nil {
+        return 0
+    }
+    var perm Permission
+    for _, policy := range u.ActiveRole.Policies {
+        for pat, p := range policy.Scopes {
+            if MatchScope(pat, scope) {
+                perm |= p
+            }
+        }
+    }
+    return perm
+}
+
+func (u *User) HasPermission(scope string, requiredPerm Permission) bool {
+    effective := u.EffectivePermissions(scope)
+    return (effective & requiredPerm) == requiredPerm
+}
+```
+
+### 4. Integration in die API-Handler
+
+- Anpassung der `jwt_auth.go` Middleware.
+- Verwendung von `HasPermission` in den API-Handlern.
+
+## Persistierung (Datenbank)
+
+### 1. Datenbankmodell
+
+- Zwei neue Tabellen: `roles` und `policies`.
+- `roles`:
+    - `id` (ULID, Primärschlüssel)
+    - `name` (VARCHAR, eindeutig)
+- `policies`:
+    - `id` (ULID, Primärschlüssel)
+    - `name` (VARCHAR, eindeutig)
+    - `role_id` (ULID, Fremdschlüssel, der auf `roles.id` verweist)
+    - `scopes` (JSONB oder TEXT, speichert die `map[string]Permission` als JSON)
+- Beziehung: 1:n zwischen `roles` und `policies`.
+
+### 2. Go-Strukturen (Anpassungen)
+
+- `role.go`:
+
+```go
+package permissions
+
+import (
+	"github.com/your-org/your-project/backend/internal/types" // Pfad anpassen
+)
+
+type Role struct {
+    ID       types.ULID `gorm:"primaryKey;type:bytea"`
+    Name     string     `gorm:"unique;not null"`
+    Policies []Policy   `gorm:"foreignKey:RoleID"`
+}
+```
+
+- `policy.go`:
+
+```go
+package permissions
+
+import (
+	"encoding/json"
+    "database/sql/driver"
+    "errors"
+    "fmt"
+
+	"github.com/your-org/your-project/backend/internal/types" // Pfad anpassen
+	"gorm.io/gorm"
+	"gorm.io/gorm/clause"
+)
+
+type Policy struct {
+    ID      types.ULID      `gorm:"primaryKey;type:bytea"`
+    Name    string          `gorm:"not null"`
+    RoleID  types.ULID      `gorm:"type:bytea"` //Fremdschlüssel
+    Scopes  Scopes          `gorm:"type:jsonb;not null"` // JSONB-Spalte
+}
+
+//Scopes type to handle JSON marshalling
+type Scopes map[string]Permission
+
+// Scan scan value into Jsonb, implements sql.Scanner interface
+func (j *Scopes) Scan(value interface{}) error {
+	bytes, ok := value.([]byte)
+	if !ok {
+		return errors.New(fmt.Sprint("Failed to unmarshal JSONB value:", value))
+	}
+
+	var scopes map[string]Permission
+	if err := json.Unmarshal(bytes, &scopes); err != nil {
+		return err
+	}
+	*j = scopes
+	return nil
+}
+
+// Value return json value, implement driver.Valuer interface
+func (j Scopes) Value() (driver.Value, error) {
+	return json.Marshal(j)
+}
+```
+### 3. Migration
+
+- Verwendung des vorhandenen Migrations-Frameworks (`backend/cmd/migrate/main.go`).
+
+### 4. Seed-Daten
+
+- Optionale Seed-Daten (`backend/cmd/seed/main.go`).
+
+### 5. Anpassung der Funktionen
+
+- Anpassung von `EffectivePermissions` und `HasPermission` in `evaluator.go` für Datenbankzugriff.
+
+## Mermaid Diagramm
+```mermaid
+graph LR
+    subgraph Benutzer
+        U[User] --> AR(ActiveRole)
+    end
+    subgraph Rolle
+        AR --> R(Role)
+        R --> P1(Policy 1)
+        R --> P2(Policy 2)
+        R --> Pn(Policy n)
+    end
+    subgraph Policy
+        P1 --> S1(Scope 1: Permissions)
+        P1 --> S2(Scope 2: Permissions)
+        P2 --> S3(Scope 3: Permissions)
+        Pn --> Sm(Scope m: Permissions)
+    end
+
+    S1 -- Permissions --> PR(PermRead)
+    S1 -- Permissions --> PW(PermWrite)
+    S2 -- Permissions --> PL(PermList)
+    Sm -- Permissions --> PD(PermDelete)
+    
+    style U fill:#f9f,stroke:#333,stroke-width:2px
+    style R fill:#ccf,stroke:#333,stroke-width:2px
+    style P1,P2,Pn fill:#ddf,stroke:#333,stroke-width:2px
+    style S1,S2,S3,Sm fill:#eef,stroke:#333,stroke-width:1px
+    style PR,PW,PL,PD fill:#ff9,stroke:#333,stroke-width:1px

flake.nix

@@ -0,0 +1,113 @@
+{
+  description = "Development environment for Go and Next.js (TypeScript)";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs {
+          inherit system;
+          config = {
+            allowUnfree = true;
+          };
+        };
+
+        # Go development tools
+        goPackages = with pkgs; [
+          go
+          gopls
+          golangci-lint
+          delve
+          go-outline
+          gotools
+          go-mockgen
+          gomodifytags
+          impl
+          gotests
+        ];
+
+        # TypeScript/Next.js development tools
+        nodePackages = with pkgs; [
+          nodejs_20
+          nodePackages.typescript
+          nodePackages.typescript-language-server
+          nodePackages.yarn
+          nodePackages.pnpm
+          nodePackages.npm
+          nodePackages.prettier
+          nodePackages.eslint
+          nodePackages.next
+        ];
+
+        # General development tools
+        commonPackages = with pkgs; [
+          git
+          gh
+          nixpkgs-fmt
+          pre-commit
+          ripgrep
+          jq
+          curl
+          coreutils
+          gnumake
+        ];
+
+        # VSCode with extensions
+        vscodeWithExtensions = pkgs.vscode-with-extensions.override {
+          vscodeExtensions = with pkgs.vscode-extensions; [
+            golang.go                   # Go support
+            esbenp.prettier-vscode      # Prettier
+            dbaeumer.vscode-eslint      # ESLint
+            ms-vscode.vscode-typescript-tslint-plugin # TypeScript
+            bradlc.vscode-tailwindcss   # Tailwind CSS support
+            jnoortheen.nix-ide          # Nix support
+          ] ++ pkgs.vscode-utils.extensionsFromVscodeMarketplace [
+            {
+              name = "nextjs";
+              publisher = "pulkitgangwar";
+              version = "1.0.6";
+              sha256 = "sha256-L6ZgqNkM0qzSiTKiGfgQB9m3U0HmwLA3NZ9nrslQjeg=";
+            }
+          ];
+        };
+
+      in
+      {
+        devShells.default = pkgs.mkShell {
+          buildInputs = goPackages ++ nodePackages ++ commonPackages ++ [ vscodeWithExtensions ];
+
+          shellHook = ''
+            echo "🚀 Welcome to the Go and Next.js (TypeScript) development environment!"
+            echo "📦 Available tools:"
+            echo "   Go: $(go version)"
+            echo "   Node: $(node --version)"
+            echo "   TypeScript: $(tsc --version)"
+            echo "   Next.js: $(npx next --version)"
+            echo ""
+            echo "🔧 Use 'code .' to open VSCode with the appropriate extensions"
+            echo "🔄 Run 'nix flake update' to update dependencies"
+          '';
+
+          # Environment variables
+          GOROOT = "${pkgs.go}/share/go";
+          GOPATH = "$(pwd)/.go";
+          GO111MODULE = "on";
+          
+          # NodeJS setup
+          NODE_OPTIONS = "--max-old-space-size=4096";
+        };
+
+        # Optional: Add custom packages if needed
+        packages = {
+          # Example of a custom package or script if needed
+          # my-tool = ...
+        };
+        
+        # Default package if someone runs `nix build`
+        defaultPackage = self.devShells.${system}.default;
+      });
+}

refactor_plan.md

@@ -0,0 +1,25 @@
+# Refactoring Plan for backend/internal/api/handlers
+
+## Goal
+
+Refactor the code in `backend/internal/api/handlers` to reduce repetition and create helper functions for boilerplate operations, utilizing functions from `backend/internal/api/utils/handler_utils.go` and creating new ones if necessary.
+
+## Analysis
+
+The following common patterns were identified in the handler files:
+
+1.  **Error Handling:** Each handler function repeats the same error handling pattern.
+2.  **DTO Binding:** Parsing the request body and handling potential errors.
+3.  **ID Parsing:** Parsing the ID from the URL and handling potential errors.
+4.  **DTO Conversion:** Converting between DTOs and models.
+5.  **Success Responses:** Calling `responses.SuccessResponse` with the appropriate HTTP status code and data.
+6.  **Not Found Responses:** Checking if a record exists and calling `responses.NotFoundResponse` if it doesn't.
+
+The `Update` handler is the most complex and has the most potential for refactoring.
+
+## Plan
+
+1.  **Implement a generic `HandleUpdate` function in `handler_utils.go`:** This function will encapsulate the common logic for updating entities, including parsing the ID, binding the JSON, converting the DTO to a model, calling the update function, and handling errors and not found cases. The function will also handle nullable fields correctly.
+2.  **Modify the existing handlers to use the new `HandleUpdate` function:** This will involve removing the duplicated code from each handler and calling the generic function instead.
+3.  **Create new helper functions in `handler_utils.go` if needed:** If there are any specific operations that are not covered by the existing utility functions, I will create new ones to handle them.
+