import 'dart:async';

import 'package:flutter_riverpod/flutter_riverpod.dart';

import '../api/note_api.dart';
import '../core/network/api_exception.dart';
import '../models/note.dart';

/// 笔记列表页状态
class NoteListState {
  final List<NoteListItem> items;
  final bool loading; // 首屏 / 刷新 / 切筛选条件
  final bool loadingMore; // 上拉加载下一页
  final String? error;
  final int page; // 已加载到第几页，0 表示还没加载
  final bool hasMore;
  final int total;
  final String keyword;
  final String tag;
  final String sort; // updated | created | title
  final NoteLocation location;

  const NoteListState({
    this.items = const [],
    this.loading = false,
    this.loadingMore = false,
    this.error,
    this.page = 0,
    this.hasMore = false,
    this.total = 0,
    this.keyword = '',
    this.tag = '',
    this.sort = 'updated',
    this.location = NoteLocation.all,
  });

  /// 真正的一条都没有（不是加载中、也不是出错）
  bool get isEmpty => items.isEmpty && !loading && error == null;

  /// 是否处于筛选态——决定空状态该显示"还没有笔记"还是"没有匹配结果"
  bool get hasFilter => keyword.isNotEmpty || tag.isNotEmpty;

  NoteListState copyWith({
    List<NoteListItem>? items,
    bool? loading,
    bool? loadingMore,
    Object? error = _sentinel,
    int? page,
    bool? hasMore,
    int? total,
    String? keyword,
    String? tag,
    String? sort,
    NoteLocation? location,
  }) {
    return NoteListState(
      items: items ?? this.items,
      loading: loading ?? this.loading,
      loadingMore: loadingMore ?? this.loadingMore,
      error: error == _sentinel ? this.error : error as String?,
      page: page ?? this.page,
      hasMore: hasMore ?? this.hasMore,
      total: total ?? this.total,
      keyword: keyword ?? this.keyword,
      tag: tag ?? this.tag,
      sort: sort ?? this.sort,
      location: location ?? this.location,
    );
  }

  static const _sentinel = Object();
}

class NoteListNotifier extends Notifier<NoteListState> {
  static const _pageSize = 20;

  Timer? _searchDebounce;

  @override
  NoteListState build() {
    ref.onDispose(() => _searchDebounce?.cancel());
    // build() 里不能同步读写 state，所以丢到微任务里再发起首次加载
    Future.microtask(() => _fetchFirstPage(
          keyword: '',
          tag: '',
          sort: 'updated',
          location: NoteLocation.all,
        ));
    return const NoteListState(loading: true);
  }

  /// 取第一页。参数由调用方传入而不是读 state，
  /// 是为了能在 build() 阶段安全调用。
  Future<void> _fetchFirstPage({
    required String keyword,
    required String tag,
    required String sort,
    required NoteLocation location,
  }) async {
    try {
      final result = await ref.read(noteApiProvider).list(
            page: 1,
            size: _pageSize,
            scope: location.apiScope,
            folderId: location.folderId,
            sort: sort,
            keyword: keyword,
            tag: tag,
          );
      if (!ref.mounted) return;
      state = state.copyWith(
        items: result.items,
        loading: false,
        error: null,
        page: 1,
        hasMore: result.hasMore,
        total: result.total,
      );
    } on ApiException catch (e) {
      if (!ref.mounted) return;
      state = state.copyWith(loading: false, error: e.message);
    } catch (_) {
      if (!ref.mounted) return;
      state = state.copyWith(loading: false, error: '笔记加载失败');
    }
  }

  /// 下拉刷新 / 详情页改动后刷新。保留当前筛选条件。
  Future<void> refresh() async {
    state = state.copyWith(loading: true, error: null);
    await _fetchFirstPage(
      keyword: state.keyword,
      tag: state.tag,
      sort: state.sort,
      location: state.location,
    );
  }

  /// 上拉加载下一页
  Future<void> loadMore() async {
    if (state.loadingMore || !state.hasMore || state.loading) return;

    state = state.copyWith(loadingMore: true);
    try {
      final next = state.page + 1;
      final result = await ref.read(noteApiProvider).list(
            page: next,
            size: _pageSize,
            scope: state.location.apiScope,
            folderId: state.location.folderId,
            sort: state.sort,
            keyword: state.keyword,
            tag: state.tag,
          );
      if (!ref.mounted) return;
      state = state.copyWith(
        // 用 id 去重：加载过程中如果有笔记被置顶/更新，
        // 它可能同时出现在两页里，直接拼接会出现重复卡片
        items: _mergeUnique(state.items, result.items),
        loadingMore: false,
        page: next,
        hasMore: result.hasMore,
        total: result.total,
      );
    } catch (_) {
      if (!ref.mounted) return;
      state = state.copyWith(loadingMore: false);
    }
  }

  List<NoteListItem> _mergeUnique(List<NoteListItem> old, List<NoteListItem> added) {
    final seen = old.map((e) => e.id).toSet();
    return [...old, ...added.where((e) => !seen.contains(e.id))];
  }

  /// 搜索关键词。带防抖，避免每敲一个字都打一次接口。
  void setKeyword(String keyword) {
    if (keyword == state.keyword) return;
    state = state.copyWith(keyword: keyword);
    _searchDebounce?.cancel();
    _searchDebounce = Timer(const Duration(milliseconds: 350), () {
      if (!ref.mounted) return;
      refresh();
    });
  }

  /// 标签筛选
  void setTag(String tag) {
    if (tag == state.tag) return;
    state = state.copyWith(tag: tag);
    refresh();
  }

  /// 切换浏览的目录
  void setLocation(NoteLocation location) {
    if (location.scope == state.location.scope &&
        location.folderId == state.location.folderId) {
      return;
    }
    state = state.copyWith(location: location);
    refresh();
  }

  /// 切换排序方式
  void setSort(String sort) {
    if (sort == state.sort) return;
    state = state.copyWith(sort: sort);
    refresh();
  }
}

/// 列表用普通 NotifierProvider（不加 autoDispose）：
/// 从详情页返回时搜索关键词、标签筛选和所在目录都要还在，不能被回收重建。
final noteListProvider =
    NotifierProvider<NoteListNotifier, NoteListState>(NoteListNotifier.new);

/// 笔记详情
final noteDetailProvider =
    FutureProvider.autoDispose.family<NoteDetail, int>((ref, id) {
  return ref.watch(noteApiProvider).detail(id);
});

/// 标签列表
final noteTagsProvider = FutureProvider.autoDispose<List<String>>((ref) {
  return ref.watch(noteApiProvider).tags();
});

/// 目录树
final noteFolderTreeProvider = FutureProvider.autoDispose<FolderTree>((ref) {
  return ref.watch(noteApiProvider).folderTree();
});