اتصال فلاتر به سرور با Dio: مدل‌ها، خطاها و ساختار تمیز

final dio = Dio(BaseOptions(
  baseUrl: 'https://api.example.com/api/v1',
  connectTimeout: const Duration(seconds: 10),
  receiveTimeout: const Duration(seconds: 20),
  headers: {'Accept': 'application/json'},
));

class Course {
  final String id;
  final String name;
  final int price;
  const Course({required this.id, required this.name, required this.price});

  factory Course.fromJson(Map<String, dynamic> json) => Course(
        id: json['id'] as String,
        name: json['name'] as String,
        price: json['price'] as int,
      );
}

class CourseRepository {
  CourseRepository(this._dio);
  final Dio _dio;

  Future<List<Course>> fetchCourses() async {
    final response = await _dio.get('/courses');
    return (response.data as List)
        .map((e) => Course.fromJson(e as Map<String, dynamic>))
        .toList();
  }
}

String friendlyMessage(Object error) {
  if (error is DioException) {
    switch (error.type) {
      case DioExceptionType.connectionTimeout:
      case DioExceptionType.receiveTimeout:
        return 'پاسخی از سرور نیامد. دوباره تلاش کنید.';
      case DioExceptionType.connectionError:
        return 'اتصال اینترنت را بررسی کنید.';
      default:
        final data = error.response?.data;
        if (data is Map && data['message'] is String) return data['message'];
    }
  }
  return 'خطای نامشخص رخ داد.';
}

dio.interceptors.add(InterceptorsWrapper(
  onRequest: (options, handler) {
    final token = tokenStore.read();
    if (token != null) options.headers['Authorization'] = 'Bearer $token';
    handler.next(options);
  },
));