import 'dart:async';

import 'package:meta/meta.dart';

// 简易的Bloc, 简易的状态管理

abstract class EasyBlocBase<State> {

  EasyBlocBase(this.state): assert(state != null);

  final StreamController<State> _stateController = StreamController<State>.broadcast();

  Stream<State> get stream => _stateController.stream;
  State state;

  bool _emitted = false;

  // 添加监听器方法
  StreamSubscription<State> listen(
      void Function(State state) onData, {
        Function? onError,
        void Function()? onDone,
        bool? cancelOnError,
      }) {
    return stream.listen(
      onData,
      onError: onError,
      onDone: onDone,
      cancelOnError: cancelOnError,
    );
  }

  // 新状态
  void emit(State newState) {
    if (_stateController.isClosed) return;
    if (newState == state && _emitted) return;
    this.state = newState;
    _stateController.add(state);
    _emitted = true;
  }

  @mustCallSuper
  Future<void> close() async {
    await _stateController.close();
  }
}

class EasyBloc<Event, State> extends EasyBlocBase<State> {
  EasyBloc(State initialState) : super(initialState) {
    _eventController.stream.listen(_mapEventToState);
  }

  final StreamController<Event> _eventController = StreamController<Event>();

  // 子类需要实现这个方法来处理事件
  @mustBeOverridden
  void _mapEventToState(Event event) {
    // 默认不做任何处理，如果不实现会抛出异常
    throw UnimplementedError('_mapEventToState must be implemented by subclasses');
  }

  // 添加事件
  void add(Event event) {
    if (_eventController.isClosed) return;
    _eventController.add(event);
  }

  @override
  Future<void> close() async {
    await _eventController.close();
    await super.close();
  }
}

class EasyCubit<State> extends EasyBlocBase<State> {
  EasyCubit(State initialState) : super(initialState);
}