// lib/services/audio_service.dart
import 'dart:async';
import 'package:flutter/material.dart';
import 'package:media_kit/media_kit.dart';
import 'playback_service.dart';

// ============================================================
// 播放模式
// ============================================================
enum PlayMode {
  sequential, // 顺序循环
  repeatOne, // 单曲循环
  shuffle, // 随机播放
}

// ============================================================
// 歌曲模型
// ============================================================
class Song {
  final String id;
  final String title;
  final String artist;
  final String? url;

  Song({
    required this.id,
    required this.title,
    required this.artist,
    this.url,
  });
}

// ============================================================
// AudioService - 播放状态管理与 UI 数据源
// ============================================================
class AudioService extends ChangeNotifier {
  // ---------- 单例 ----------
  static final AudioService _instance = AudioService._internal();
  factory AudioService() => _instance;
  AudioService._internal();

  // ---------- 播放状态 ----------
  Song? _currentSong;
  bool _isPlaying = false;
  Duration _position = Duration.zero;
  Duration _duration = Duration.zero;
  Duration _bufferedPosition = Duration.zero;

  // ---------- 播放模式 ----------
  PlayMode _playMode = PlayMode.sequential;

  // ---------- 播放队列 ----------
  List<Song> _queue = [];
  int _currentIndex = -1;

  // ---------- 随机播放相关 ----------
  List<int> _shuffledIndices = [];
  int _shuffledIndex = -1;

  // ---------- 监听控制 ----------
  bool _listening = false;
  final List<StreamSubscription> _subscriptions = [];

  // ---------- Getter ----------
  Song? get currentSong => _currentSong;
  bool get isPlaying => _isPlaying;
  Duration get position => _position;
  Duration get duration => _duration;
  Duration get bufferedPosition => _bufferedPosition;
  PlayMode get playMode => _playMode;
  List<Song> get queue => List.unmodifiable(_queue);
  int get currentIndex => _currentIndex;
  bool get hasQueue => _queue.isNotEmpty;

  // ---------- 播放模式图标 ----------
  IconData get playModeIcon {
    switch (_playMode) {
      case PlayMode.sequential:
        return Icons.repeat;
      case PlayMode.repeatOne:
        return Icons.repeat_one;
      case PlayMode.shuffle:
        return Icons.shuffle;
    }
  }

  // ---------- 播放模式切换 ----------
  void togglePlayMode() {
    switch (_playMode) {
      case PlayMode.sequential:
        _playMode = PlayMode.repeatOne;
        break;
      case PlayMode.repeatOne:
        _playMode = PlayMode.shuffle;
        break;
      case PlayMode.shuffle:
        _playMode = PlayMode.sequential;
        break;
    }
    notifyListeners();
  }

  // ---------- 设置播放队列 ----------
  void setQueue(List<Song> queue, {int startIndex = 0}) {
    if (queue.isEmpty) {
      _clearQueue();
      return;
    }

    _queue = List.from(queue);
    _currentIndex = startIndex.clamp(0, _queue.length - 1);

    // 初始化随机播放索引
    _shuffledIndices = List.generate(_queue.length, (i) => i);
    _shuffledIndices.shuffle();
    _shuffledIndex = _shuffledIndices.indexOf(_currentIndex);
    if (_shuffledIndex == -1) {
      _shuffledIndex = 0;
      _currentIndex = _shuffledIndices[0];
    }

    // 播放当前歌曲
    _playCurrent();
  }

  // ---------- 清空队列 ----------
  void _clearQueue() {
    _queue.clear();
    _currentIndex = -1;
    _shuffledIndices.clear();
    _shuffledIndex = -1;
    stopPlay();
  }

  // ---------- 播放指定歌曲（外部入口） ----------
  Future<void> playSong(Song song) async {
    // 如果当前队列不包含这首歌，替换队列
    if (_queue.isEmpty || _queue[_currentIndex].id != song.id) {
      setQueue([song], startIndex: 0);
    } else {
      // 如果已经在队列中，直接播放
      _playCurrent();
    }
  }

  // ---------- 播放当前索引歌曲 ----------
  void _playCurrent() {
    if (_currentIndex < 0 || _currentIndex >= _queue.length) {
      stopPlay();
      return;
    }

    final song = _queue[_currentIndex];
    _currentSong = song;
    _position = Duration.zero;
    _duration = Duration.zero;
    _bufferedPosition = Duration.zero;

    _startListening();
    notifyListeners();

    if (song.url == null || song.url!.isEmpty) {
      return;
    }

    // 由 PlaybackService 实际播放，状态由流更新
    PlaybackService().play(song.url!);
  }

  // ---------- 播放下一首 ----------
  void next() {
    if (_queue.isEmpty) return;

    // 随机模式
    if (_playMode == PlayMode.shuffle) {
      if (_shuffledIndices.isEmpty) return;
      final nextIdx = (_shuffledIndex + 1) % _shuffledIndices.length;
      _shuffledIndex = nextIdx;
      _currentIndex = _shuffledIndices[nextIdx];
      _playCurrent();
      return;
    }

    // 顺序/单曲模式
    final nextIdx = (_currentIndex + 1) % _queue.length;
    _currentIndex = nextIdx;
    _playCurrent();
  }

  // ---------- 播放上一首 ----------
  void previous() {
    if (_queue.isEmpty) return;

    // 随机模式
    if (_playMode == PlayMode.shuffle) {
      if (_shuffledIndices.isEmpty) return;
      final prevIdx = (_shuffledIndex - 1) % _shuffledIndices.length;
      if (prevIdx < 0) {
        _shuffledIndex = _shuffledIndices.length - 1;
      } else {
        _shuffledIndex = prevIdx;
      }
      _currentIndex = _shuffledIndices[_shuffledIndex];
      _playCurrent();
      return;
    }

    // 顺序/单曲模式
    final prevIdx = (_currentIndex - 1) % _queue.length;
    if (prevIdx < 0) {
      _currentIndex = _queue.length - 1;
    } else {
      _currentIndex = prevIdx;
    }
    _playCurrent();
  }

  // ---------- 播放/暂停切换 ----------
  void togglePlay() {
    if (_currentSong == null) return;

    if (_isPlaying) {
      PlaybackService().pause();
    } else {
      PlaybackService().resume();
    }
    // 状态由 player.stream.playing 更新
  }

  // ---------- 停止播放 ----------
  void stopPlay() {
    _currentSong = null;
    _isPlaying = false;
    _position = Duration.zero;
    _duration = Duration.zero;
    _bufferedPosition = Duration.zero;
    _stopListening();
    notifyListeners();
  }

  // ---------- Seek ----------
  void seekTo(Duration position) {
    PlaybackService().seek(position);
    _position = position;
    notifyListeners();
  }

  // ---------- 处理播放结束 ----------
  void _onPlaybackCompleted() {
    if (_queue.isEmpty) return;

    // 单曲循环模式
    if (_playMode == PlayMode.repeatOne) {
      _playCurrent();
      return;
    }

    // 其他模式：播放下一首
    next();
  }

  void clearQueue() {
    _queue.clear();
    _currentIndex = -1;
    _shuffledIndices.clear();
    _shuffledIndex = -1;
    stopPlay();
    notifyListeners();
  }

  // ---------- 监听 media_kit 状态 ----------
  void _startListening() {
    if (_listening) return;
    _listening = true;

    final player = PlaybackService().player;

    _subscriptions.add(
      player.stream.playing.listen((playing) {
        if (_isPlaying != playing) {
          _isPlaying = playing;
          notifyListeners();
        }
      }),
    );

    _subscriptions.add(
      player.stream.position.listen((position) {
        if (_position != position) {
          _position = position;
          notifyListeners();
        }
      }),
    );

    _subscriptions.add(
      player.stream.duration.listen((duration) {
        if (_duration != duration) {
          _duration = duration;
          notifyListeners();
        }
      }),
    );

    _subscriptions.add(
      player.stream.buffer.listen((buffer) {
        if (_bufferedPosition != buffer) {
          _bufferedPosition = buffer;
          notifyListeners();
        }
      }),
    );

    // ✅ 播放结束监听
    _subscriptions.add(
      player.stream.completed.listen((_) {
        _onPlaybackCompleted();
      }),
    );
  }

  void _stopListening() {
    _listening = false;
    for (final subscription in _subscriptions) {
      subscription.cancel();
    }
    _subscriptions.clear();
  }

  // ---------- 资源释放 ----------
  void dispose() {
    _stopListening();
    PlaybackService().dispose();
    super.dispose();
  }
}