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lib/features/auth/domain/usecases/login_usecase.dart

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+import 'package:dartz/dartz.dart';
+
+import '../../../../core/errors/failures.dart';
+import '../../data/models/login_request_model.dart';
+import '../entities/user_entity.dart';
+import '../repositories/auth_repository.dart';
+
+/// Use case for user login
+///
+/// Encapsulates the business logic for authentication
+/// Validates input, calls repository, and handles the response
+class LoginUseCase {
+  final AuthRepository repository;
+
+  LoginUseCase(this.repository);
+
+  /// Execute login operation
+  ///
+  /// [request] - Login credentials (username and password)
+  ///
+  /// Returns [Right(UserEntity)] on successful login
+  /// Returns [Left(Failure)] on error:
+  /// - [ValidationFailure] if credentials are invalid
+  /// - [AuthenticationFailure] if login fails
+  /// - [NetworkFailure] if network error occurs
+  Future<Either<Failure, UserEntity>> call(LoginRequestModel request) async {
+    // Validate input
+    final validationError = _validateInput(request);
+    if (validationError != null) {
+      return Left(validationError);
+    }
+
+    // Call repository to perform login
+    return await repository.login(request);
+  }
+
+  /// Validate login request input
+  ///
+  /// Returns [ValidationFailure] if validation fails, null otherwise
+  ValidationFailure? _validateInput(LoginRequestModel request) {
+    // Validate username
+    if (request.username.trim().isEmpty) {
+      return const ValidationFailure('Username is required');
+    }
+
+    if (request.username.length < 3) {
+      return const ValidationFailure('Username must be at least 3 characters');
+    }
+
+    // Validate password
+    if (request.password.isEmpty) {
+      return const ValidationFailure('Password is required');
+    }
+
+    if (request.password.length < 6) {
+      return const ValidationFailure('Password must be at least 6 characters');
+    }
+
+    return null;
+  }
+}
+
+/// Use case for user logout
+class LogoutUseCase {
+  final AuthRepository repository;
+
+  LogoutUseCase(this.repository);
+
+  /// Execute logout operation
+  ///
+  /// Returns [Right(void)] on successful logout
+  /// Returns [Left(Failure)] on error
+  Future<Either<Failure, void>> call() async {
+    return await repository.logout();
+  }
+}
+
+/// Use case for checking authentication status
+class CheckAuthStatusUseCase {
+  final AuthRepository repository;
+
+  CheckAuthStatusUseCase(this.repository);
+
+  /// Check if user is authenticated
+  ///
+  /// Returns true if user has valid access token
+  Future<bool> call() async {
+    return await repository.isAuthenticated();
+  }
+}
+
+/// Use case for getting current user
+class GetCurrentUserUseCase {
+  final AuthRepository repository;
+
+  GetCurrentUserUseCase(this.repository);
+
+  /// Get current authenticated user
+  ///
+  /// Returns [Right(UserEntity)] if user is authenticated
+  /// Returns [Left(Failure)] if no user found or error occurs
+  Future<Either<Failure, UserEntity>> call() async {
+    return await repository.getCurrentUser();
+  }
+}
+
+/// Use case for refreshing access token
+class RefreshTokenUseCase {
+  final AuthRepository repository;
+
+  RefreshTokenUseCase(this.repository);
+
+  /// Refresh access token using refresh token
+  ///
+  /// [refreshToken] - The refresh token
+  ///
+  /// Returns [Right(UserEntity)] with new tokens on success
+  /// Returns [Left(Failure)] on error
+  Future<Either<Failure, UserEntity>> call(String refreshToken) async {
+    if (refreshToken.isEmpty) {
+      return const Left(ValidationFailure('Refresh token is required'));
+    }
+
+    return await repository.refreshToken(refreshToken);
+  }
+}