Architecture Layers বিস্তারিত

Clean Architecture-এ Flutter applications তিনটি প্রধান layer-এ বিভক্ত। প্রতিটি layer-এর নিজস্ব দায়িত্ব এবং structure রয়েছে।

🎯 Domain Layer (Core Business Logic)

Domain Layer হল Clean Architecture-এর হৃদয়। এটি সবচেয়ে inner layer এবং কোনো external dependencies নেই।

📦 Components

🏷 Entities

Business objects যা application-এর core data represent করে।

class User {
  final String id;
  final String name;
  final String email;
  final DateTime createdAt;
  
  const User({
    required this.id,
    required this.name,
    required this.email,
    required this.createdAt,
  });
}

🎯 Use Cases

Specific business operations বা actions। একটি use case একটি নির্দিষ্ট কাজ করে।

class GetUserProfileUseCase {
  final UserRepository _repository;
  
  GetUserProfileUseCase(this._repository);
  
  Future<User> call(String userId) async {
    return await _repository.getUserById(userId);
  }
}

📋 Repository Interfaces

Data layer-এর সাথে communication-এর জন্য abstract contracts।

abstract class UserRepository {
  Future<User> getUserById(String id);
  Future<List<User>> getAllUsers();
  Future<User> createUser(User user);
  Future<User> updateUser(User user);
  Future<void> deleteUser(String id);
}

✅ Domain Layer-এর নিয়ম

• কোনো external dependencies নেই
• শুধুমাত্র Dart core libraries ব্যবহার করে
• Business logic এবং rules এখানে থাকে
• UI বা database সম্পর্কে কিছু জানে না

📊 Data Layer (External Data Management)

Data Layer external data sources (API, Database, Cache) থেকে data handle করে।

📦 Components

🏗 Models

API response এবং database entities represent করে। JSON serialization এখানে হয়।

@freezed
class UserModel with _$UserModel {
  const factory UserModel({
    required String id,
    required String name,
    required String email,
    required String createdAt,
  }) = _UserModel;
  
  factory UserModel.fromJson(Map<String, dynamic> json) => 
      _$UserModelFromJson(json);
}

extension UserModelX on UserModel {
  User toEntity() {
    return User(
      id: id,
      name: name,
      email: email,
      createdAt: DateTime.parse(createdAt),
    );
  }
}

🌐 Data Sources

External APIs বা local databases-এর সাথে communication।

abstract class UserRemoteDataSource {
  Future<UserModel> getUserById(String id);
  Future<List<UserModel>> getAllUsers();
  Future<UserModel> createUser(UserModel user);
}

class UserRemoteDataSourceImpl implements UserRemoteDataSource {
  final Dio _dio;
  
  UserRemoteDataSourceImpl(this._dio);
  
  @override
  Future<UserModel> getUserById(String id) async {
    final response = await _dio.get('/users/$id');
    return UserModel.fromJson(response.data);
  }
}

🔄 Repository Implementations

Domain layer-এর repository interfaces implement করে।

class UserRepositoryImpl implements UserRepository {
  final UserRemoteDataSource _remoteDataSource;
  final UserLocalDataSource _localDataSource;
  
  UserRepositoryImpl(this._remoteDataSource, this._localDataSource);
  
  @override
  Future<User> getUserById(String id) async {
    try {
      final userModel = await _remoteDataSource.getUserById(id);
      await _localDataSource.cacheUser(userModel);
      return userModel.toEntity();
    } catch (e) {
      final cachedUser = await _localDataSource.getCachedUser(id);
      return cachedUser.toEntity();
    }
  }
}

✅ Data Layer-এর নিয়ম

• Domain layer-এর interfaces implement করে
• External dependencies (HTTP, Database) এখানে থাকে
• Data transformation (Model ↔ Entity) এখানে হয়
• Error handling এবং caching logic এখানে থাকে

🖥 Presentation Layer (UI & User Interaction)

Presentation Layer user interface এবং user interactions handle করে।

📦 Components

📱 Pages/Screens

UI components যা user দেখে এবং interact করে।

class UserProfilePage extends StatelessWidget {
  const UserProfilePage({Key? key}) : super(key: key);
  
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Profile')),
      body: BlocBuilder<UserProfileBloc, UserProfileState>(
        builder: (context, state) {
          if (state is UserProfileLoading) {
            return Center(child: CircularProgressIndicator());
          }
          
          if (state is UserProfileLoaded) {
            return UserProfileView(user: state.user);
          }
          
          return Center(child: Text('Error loading user'));
        },
      ),
    );
  }
}

🎮 Controllers/BLoC

State management এবং business logic calls।

GetX Controller:

class UserController extends GetxController {
  final GetUserProfileUseCase _getUserProfileUseCase;
  
  UserController(this._getUserProfileUseCase);
  
  final _user = Rx<User?>(null);
  final _isLoading = false.obs;
  
  User? get user => _user.value;
  bool get isLoading => _isLoading.value;
  
  Future<void> loadUserProfile(String userId) async {
    try {
      _isLoading.value = true;
      final user = await _getUserProfileUseCase(userId);
      _user.value = user;
    } catch (e) {
      Get.snackbar('Error', 'Failed to load user profile');
    } finally {
      _isLoading.value = false;
    }
  }
}

BLoC:

class UserProfileBloc extends Bloc<UserProfileEvent, UserProfileState> {
  final GetUserProfileUseCase _getUserProfileUseCase;
  
  UserProfileBloc(this._getUserProfileUseCase) : super(UserProfileInitial()) {
    on<LoadUserProfile>(_onLoadUserProfile);
  }
  
  Future<void> _onLoadUserProfile(
    LoadUserProfile event,
    Emitter<UserProfileState> emit,
  ) async {
    emit(UserProfileLoading());
    try {
      final user = await _getUserProfileUseCase(event.userId);
      emit(UserProfileLoaded(user));
    } catch (e) {
      emit(UserProfileError(e.toString()));
    }
  }
}

🔗 Bindings/Providers

Dependency injection setup।

GetX Binding:

class UserBinding extends Bindings {
  @override
  void dependencies() {
    Get.lazyPut<UserRemoteDataSource>(
      () => UserRemoteDataSourceImpl(Get.find()),
    );
    
    Get.lazyPut<UserRepository>(
      () => UserRepositoryImpl(Get.find(), Get.find()),
    );
    
    Get.lazyPut<GetUserProfileUseCase>(
      () => GetUserProfileUseCase(Get.find()),
    );
    
    Get.lazyPut<UserController>(
      () => UserController(Get.find()),
    );
  }
}

✅ Presentation Layer-এর নিয়ম

• শুধুমাত্র Domain layer-এর সাথে communicate করে
• UI state management এখানে হয়
• User input validation এখানে হয়
• Navigation logic এখানে থাকে

🔄 Layer Communication Flow

sequenceDiagram
    participant UI as 🖥 UI (Page)
    participant Controller as 🎮 Controller/BLoC
    participant UseCase as 🎯 Use Case
    participant Repo as 📋 Repository Interface
    participant RepoImpl as 🔄 Repository Impl
    participant DataSource as 🌐 Data Source
    participant API as 🌍 External API
    
    UI->>Controller: User Action
    Controller->>UseCase: Execute Business Logic
    UseCase->>Repo: Request Data
    RepoImpl->>DataSource: Fetch Data
    DataSource->>API: HTTP Request
    API-->>DataSource: Response Data
    DataSource-->>RepoImpl: Model Data
    RepoImpl-->>UseCase: Entity Data
    UseCase-->>Controller: Business Result
    Controller-->>UI: Update UI State

📚 Next Steps

Layer structure বুঝার পর folder organization দেখুন:

• 📂 Folder Structure - Project-এ কিভাবে organize করবেন
• 🔄 Workflow - Development workflow এবং best practices

---

💡 Pro Tip: প্রতিটি layer-এর দায়িত্ব আলাদা রাখুন। Mixing layers হল সবচেয়ে common mistake!