made use of first class citizen objects as json validator functions

backend-dart/lib/common/request_helper.dart

@@ -28,4 +28,4 @@ TaskEither<IError, T> decodeJson<T>(
       message: 'Failed to decode JSON: ${error.toString()}',
     ),
   );
-}
+}

backend-dart/lib/common/response_helpers.dart

@@ -1,8 +1,24 @@
 import 'dart:convert';
 import 'package:backend_dart/domain/errors/error_code.dart';
 import 'package:backend_dart/domain/interface/error.dart';
+import 'package:fpdart/fpdart.dart';
 import 'package:shelf/shelf.dart';
 
+extension TaskEitherResponseExtensions
+    on TaskEither<IError, Map<String, dynamic>> {
+  Task<Response> toResponse() => match(
+        (left) => ResponseHelpers.fromError(left),
+        (right) => ResponseHelpers.jsonOk(right),
+      );
+}
+
+extension TaskEitherResponseExtensionsFromString on TaskEither<IError, String> {
+  Task<Response> toResponse() => match(
+        (left) => ResponseHelpers.fromError(left),
+        (right) => Response.ok(right),
+      );
+}
+
 class ResponseHelpers {
   /// Sendet eine JSON-Antwort mit einem 200-Statuscode
   static Response jsonOk(Map<String, dynamic> data) {

backend-dart/lib/common/validation.dart

@@ -1,22 +1,18 @@
 import 'package:backend_dart/domain/errors/app_error.dart';
-import 'package:backend_dart/domain/interface/error.dart';
 import 'package:fpdart/fpdart.dart';
 
-TaskEither<IError, Map<String, dynamic>> validateJsonKeys(
-    Map<String, dynamic> json, List<String> requiredKeys) {
-  return TaskEither.tryCatch(
-    () async {
-      final missingKeys =
-          requiredKeys.where((key) => !json.containsKey(key)).toList();
+TaskEither<AppError, Map<String, dynamic>> Function(Map<String, dynamic>)
+    validateJsonKeys(List<String> requiredKeys) {
+  return (json) {
+    final missingKeys =
+        requiredKeys.where((key) => !json.containsKey(key)).toList();
 
-      if (missingKeys.isNotEmpty) {
-        throw Exception('Missing required keys: ${missingKeys.join(', ')}');
-      }
+    if (missingKeys.isNotEmpty) {
+      return TaskEither.left(AppError.validationError(
+        message: 'Missing required keys: ${missingKeys.join(', ')}',
+      ));
+    }
 
-      return json;
-    },
-    (error, _) => AppError.validationError(
-      message: 'Failed to validate JSON keys: ${error.toString()}',
-    ),
-  );
+    return TaskEither.right(json);
+  };
 }