import 'package:flutter/foundation.dart';
import 'package:patbond_flutter/core/network/api_exception.dart';
import 'package:patbond_flutter/features/community/community_models.dart';
import 'package:patbond_flutter/features/community/community_repository.dart';
import 'package:patbond_flutter/features/community/toggle_sync.dart';

/// Feed 首屏四态（同 pets 先例）。
enum FeedPhase { initial, loading, ready, error }

/// 尾部加载更多三态（游标累积流新增，pets 无此并发点）。
enum LoadMorePhase { idle, loading, error }

/// community feature 状态控制器（03 号评估 §2 分层：
/// Page/Widget → CommunityController → CommunityRepository → ApiClient）。
///
/// Tab 级单例（app.dart 装配注入主壳）：Feed 是游标累积流，且详情页与
/// 首页共享同一份帖子内存副本（点赞状态跨页一致），不做页面级 state。
/// 评论列表只属详情页，按「页面级状态按页自建」纪律经 [repository]
/// 自取，不膨胀本控制器。服务端是唯一事实来源，内存副本仅作展示缓存。
class CommunityController extends ChangeNotifier {
  CommunityController({required this._repository}) {
    _likeSync = ToggleSync(
      read: (id) {
        final post = _postCache[id];
        if (post != null) {
          return ToggleReading(active: post.likedByMe, count: post.likeCount);
        }
        final card = _cardOrNull(id);
        if (card == null) return null;
        return ToggleReading(active: card.likedByMe, count: card.likeCount);
      },
      write: (id, active, count) =>
          _writeInteraction(id, likedByMe: active, likeCount: count),
      send: (id, target) async {
        final state = target
            ? await _repository.likePost(id)
            : await _repository.unlikePost(id);
        return ToggleOutcome(active: state.liked, count: state.likeCount);
      },
      generation: () => _generation,
      onError: _onToggleError,
    );
    _bookmarkSync = ToggleSync(
      read: (id) {
        final post = _postCache[id];
        if (post != null) {
          return ToggleReading(
            active: post.bookmarkedByMe,
            count: post.bookmarkCount,
          );
        }
        final card = _cardOrNull(id);
        if (card == null) return null;
        return ToggleReading(
          active: card.bookmarkedByMe,
          count: card.bookmarkCount,
        );
      },
      write: (id, active, count) =>
          _writeInteraction(id, bookmarkedByMe: active, bookmarkCount: count),
      send: (id, target) async {
        final state = target
            ? await _repository.bookmarkPost(id)
            : await _repository.unbookmarkPost(id);
        return ToggleOutcome(
          active: state.bookmarked,
          count: state.bookmarkCount,
        );
      },
      generation: () => _generation,
      onError: _onToggleError,
    );
  }

  final CommunityRepository _repository;

  /// 页面级状态（评论列表、我的帖子、收藏页等）按页直接经仓库取数。
  CommunityRepository get repository => _repository;

  late final ToggleSync _likeSync;
  late final ToggleSync _bookmarkSync;

  FeedPhase _phase = FeedPhase.initial;
  LoadMorePhase _loadMorePhase = LoadMorePhase.idle;
  List<FeedCard> _feed = const [];
  String? _nextCursor;
  bool _hasMore = false;

  /// 首屏加载失败（error 态时非 null）。
  ApiException? _lastError;

  /// 刷新失败但旧列表被保留时的错误（页面 SnackBar 轻提示后消费）。
  ApiException? _refreshError;

  /// 加载更多失败（尾部重试条渲染依据）。
  ApiException? _loadMoreError;

  /// 最近一次点赞/收藏对账失败（T3-15/16 SnackBar 消费）。
  ApiException? _toggleError;

  /// 刷新代次：整体替换列表后，在途旧代次响应（尾页 / 互动对账）一律丢弃。
  int _generation = 0;

  /// 详情内存副本（详情页与 Feed 卡片互动状态同源）。
  final Map<String, Post> _postCache = {};

  bool _disposed = false;

  FeedPhase get phase => _phase;
  LoadMorePhase get loadMorePhase => _loadMorePhase;

  /// 累积的多页 Feed 缓存（服务端 published_at DESC, id DESC 原样保留）。
  List<FeedCard> get feed => _feed;
  bool get hasMore => _hasMore;

  /// ready 且列表为空 → 空态。
  bool get isEmpty => _phase == FeedPhase.ready && _feed.isEmpty;

  ApiException? get lastError => _lastError;
  ApiException? get refreshError => _refreshError;
  ApiException? get loadMoreError => _loadMoreError;
  ApiException? get toggleError => _toggleError;

  /// 详情内存副本（进入详情页先渲染缓存，再 [getPost] 拉新）。
  Post? cachedPost(String postId) => _postCache[postId];

  /// 首屏加载 / 下拉刷新：丢弃游标从头拉第一页，成功后**整体替换**累积列表。
  /// 刷新失败保留旧列表（不清空不闪空态），错误经 [refreshError] 轻提示；
  /// 首屏（空列表）失败收敛为 error 态供页面渲染 + retry。
  Future<void> refresh() async {
    _generation += 1;
    final generation = _generation;
    _lastError = null;
    _refreshError = null;
    _loadMorePhase = LoadMorePhase.idle;
    _loadMoreError = null;
    if (_feed.isEmpty) _phase = FeedPhase.loading;
    _notify();
    try {
      final page = await _repository.getFeed();
      if (generation != _generation) return; // 期间又发生过刷新/登出。
      _feed = page.items;
      _nextCursor = page.nextCursor;
      _hasMore = page.hasMore;
      _phase = FeedPhase.ready;
    } on ApiException catch (error) {
      if (generation != _generation) return;
      if (_feed.isEmpty) {
        _lastError = error;
        _phase = FeedPhase.error;
      } else {
        _refreshError = error;
      }
    }
    _notify();
  }

  /// 滚动近底加载下一页：携带上一页 nextCursor（keyset 翻页不丢不重）。
  /// 失败置 [LoadMorePhase.error] 渲染尾部重试条；期间发生过刷新的
  /// 旧代次响应直接丢弃（避免「刷新后旧尾页追加」的重复/错位）。
  Future<void> loadMore() async {
    if (_phase != FeedPhase.ready ||
        !_hasMore ||
        _loadMorePhase == LoadMorePhase.loading) {
      return;
    }
    final generation = _generation;
    _loadMorePhase = LoadMorePhase.loading;
    _loadMoreError = null;
    _notify();
    try {
      final page = await _repository.getFeed(cursor: _nextCursor);
      if (generation != _generation) return; // 旧代次尾页，丢弃。
      _feed = [..._feed, ...page.items];
      _nextCursor = page.nextCursor;
      _hasMore = page.hasMore;
      _loadMorePhase = LoadMorePhase.idle;
    } on ApiException catch (error) {
      if (generation != _generation) return;
      _loadMoreError = error;
      _loadMorePhase = LoadMorePhase.error;
    }
    _notify();
  }

  /// 拉取帖子详情并同步内存副本（Feed 卡片互动字段一并回写）。
  Future<Post> getPost(String postId) async {
    final post = await _repository.getPost(postId);
    _postCache[postId] = post;
    _syncCardFromPost(post);
    _notify();
    return post;
  }

  /// 点赞/取消点赞（乐观翻转，终态由 [ToggleSync] 对账收敛，不外抛）。
  void toggleLike(String postId) => _likeSync.toggle(postId);

  /// 收藏/取消收藏（与点赞同构）。
  void toggleBookmark(String postId) => _bookmarkSync.toggle(postId);

  /// 消费一次性 toggle 错误（SnackBar 展示后清除）。
  void clearToggleError() => _toggleError = null;

  /// 登出清空：回 initial 态、清多页缓存与详情副本、丢弃全部在途链，
  /// 避免上一账号数据跨会话泄漏；重登后主壳重建，Feed 页重新触发 [refresh]。
  void reset() {
    _generation += 1;
    _phase = FeedPhase.initial;
    _loadMorePhase = LoadMorePhase.idle;
    _feed = const [];
    _nextCursor = null;
    _hasMore = false;
    _lastError = null;
    _refreshError = null;
    _loadMoreError = null;
    _toggleError = null;
    _postCache.clear();
    _likeSync.reset();
    _bookmarkSync.reset();
    _notify();
  }

  FeedCard? _cardOrNull(String postId) {
    for (final card in _feed) {
      if (card.id == postId) return card;
    }
    return null;
  }

  /// 互动字段统一写入口：详情副本与 Feed 卡片同步更新后 notify（同帧反馈）。
  void _writeInteraction(
    String postId, {
    bool? likedByMe,
    int? likeCount,
    bool? bookmarkedByMe,
    int? bookmarkCount,
  }) {
    final post = _postCache[postId];
    if (post != null) {
      _postCache[postId] = post.copyWithInteraction(
        likedByMe: likedByMe,
        likeCount: likeCount,
        bookmarkedByMe: bookmarkedByMe,
        bookmarkCount: bookmarkCount,
      );
    }
    final index = _feed.indexWhere((card) => card.id == postId);
    if (index != -1) {
      _feed = [..._feed]
        ..[index] = _feed[index].copyWithInteraction(
          likedByMe: likedByMe,
          likeCount: likeCount,
          bookmarkedByMe: bookmarkedByMe,
          bookmarkCount: bookmarkCount,
        );
    }
    if (post != null || index != -1) _notify();
  }

  void _syncCardFromPost(Post post) {
    final index = _feed.indexWhere((card) => card.id == post.id);
    if (index == -1) return;
    _feed = [..._feed]
      ..[index] = _feed[index].copyWithInteraction(
        likedByMe: post.likedByMe,
        likeCount: post.likeCount,
        commentCount: post.commentCount,
        bookmarkedByMe: post.bookmarkedByMe,
        bookmarkCount: post.bookmarkCount,
      );
  }

  void _onToggleError(String postId, Object error) {
    if (error is ApiException) {
      _toggleError = error;
    } else {
      _toggleError = ApiNetworkException('$error');
    }
    _notify();
  }

  void _notify() {
    if (!_disposed) notifyListeners();
  }

  @override
  void dispose() {
    _disposed = true;
    super.dispose();
  }
}