feat: refactor code

lib/feature/auth/domain/entities/user_entity.dart

@@ -0,0 +1,16 @@
+/// موجودیتِ کاربر (نام نمایشی و آواتار برای استفاده در UI).
+class UserEntity {
+  final int id;
+  final String mobile;
+  final String? firstName;
+  final String? avatar;
+
+  const UserEntity({
+    required this.id,
+    required this.mobile,
+    this.firstName,
+    this.avatar,
+  });
+
+  bool get hasName => firstName != null && firstName!.trim().isNotEmpty;
+}

lib/feature/auth/domain/repository/auth_repository.dart

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+import '../../../../core/resources/data_state.dart';
+import '../../../../core/usecase/use_case.dart';
+import '../entities/user_entity.dart';
+
+/// قرارداد لایه‌ی داده‌ی احراز هویت (پیاده‌سازی در data/repository).
+abstract class AuthRepository {
+  Future<DataState<String>> loginOtp(String mobile);
+
+  /// بررسی کد؛ توکن را ذخیره کرده و کاربرِ احرازشده را برمی‌گرداند.
+  Future<DataState<UserEntity>> checkOtp(OtpParams params);
+
+  Future<DataState<UserEntity>> updateProfile(ProfileParams params);
+
+  Future<DataState<String>> logout();
+
+  Future<bool> isLoggedIn();
+}

lib/feature/auth/domain/use_cases/check_otp_usecase.dart

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+import '../../../../core/resources/data_state.dart';
+import '../../../../core/usecase/use_case.dart';
+import '../entities/user_entity.dart';
+import '../repository/auth_repository.dart';
+
+class CheckOtpUseCase implements UseCase<DataState<UserEntity>, OtpParams> {
+  final AuthRepository repository;
+  CheckOtpUseCase(this.repository);
+
+  @override
+  Future<DataState<UserEntity>> call(OtpParams params) =>
+      repository.checkOtp(params);
+}

lib/feature/auth/domain/use_cases/login_usecase.dart

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+import '../../../../core/resources/data_state.dart';
+import '../../../../core/usecase/use_case.dart';
+import '../repository/auth_repository.dart';
+
+class LoginUseCase implements UseCase<DataState<String>, String> {
+  final AuthRepository repository;
+  LoginUseCase(this.repository);
+
+  @override
+  Future<DataState<String>> call(String params) => repository.loginOtp(params);
+}

lib/feature/auth/domain/use_cases/logout_usecase.dart

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+import '../../../../core/resources/data_state.dart';
+import '../../../../core/usecase/use_case.dart';
+import '../repository/auth_repository.dart';
+
+class LogoutUseCase implements UseCase<DataState<String>, NoParams> {
+  final AuthRepository repository;
+  LogoutUseCase(this.repository);
+
+  @override
+  Future<DataState<String>> call(NoParams params) => repository.logout();
+}

lib/feature/auth/domain/use_cases/update_profile_usecase.dart

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+import '../../../../core/resources/data_state.dart';
+import '../../../../core/usecase/use_case.dart';
+import '../entities/user_entity.dart';
+import '../repository/auth_repository.dart';
+
+class UpdateProfileUseCase
+    implements UseCase<DataState<UserEntity>, ProfileParams> {
+  final AuthRepository repository;
+  UpdateProfileUseCase(this.repository);
+
+  @override
+  Future<DataState<UserEntity>> call(ProfileParams params) =>
+      repository.updateProfile(params);
+}