main.dart

main.dart

void main() {
  const mockData = {
    "code": 200,
    "success": true,
    "data": {
      "name": "Jan",
      "age": 20,
    }
  };

  const mockPageData = {
    "code": 200,
    "success": true,
    "data": [
      {
        "name": "Jan",
        "age": 20,
      },
      {
        "name": "John",
        "age": 18,
      },
    ]
  };

  final data = Response<User>.fromJson(mockData, User.decode);
  print(data);

  final pageData = PagedResponse<User>.fromJson(mockPageData, User.decode);
  print(pageData);
}

typedef Decode<T> = T? Function(Map<String, dynamic>);

abstract class BaseResponse {
  int code;
  bool success;
  BaseResponse({required this.code, required this.success});
}

class Response<T> extends BaseResponse {
  T? data;

  Response({required super.code, required super.success, required this.data});

  factory Response.fromJson(Map<String, dynamic> json, Decode<T> decode) {
    return Response(
      code: json["code"] as int,
      success: json["success"] as bool,
      data: decode(json["data"]),
    );
  }

  @override
  String toString() {
    return "code: $code, success: $success, data: $data";
  }
}

class PagedResponse<T> extends BaseResponse {
  List<T>? data;

  PagedResponse(
      {required super.code, required super.success, required this.data});

  factory PagedResponse.fromJson(Map<String, dynamic> json, Decode<T> decode) {
    final _data = json["data"];
    if (_data is! List) {
      throw RequestError.format(message: "data is not available");
    }

    return PagedResponse(
      code: json["code"] as int,
      success: json["success"] as bool,
      data: List.from(_data.map((item) => decode(item)).whereType<T>()),
    );
  }

  @override
  String toString() {
    return "code: $code, success: $success, data: $data";
  }
}

class RequestError extends Error {
  String message;
  RequestError(this.message);

  factory RequestError.format({String? message}) {
    return RequestError(message ?? "format error");
  }

  @override
  String toString() {
    return "error: $message";
  }
}

class User {
  String name;
  int age;

  User({required this.name, required this.age});

  static User? decode(Map<String, dynamic> json) {
    return User(
      name: json["name"] as String,
      age: json["age"] as int,
    );
  }

  @override
  String toString() {
    return "name: $name, age: $age";
  }
}