import 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:go_router/go_router.dart';

import '../../core/theme/app_theme.dart';
import '../../models/video_item.dart';
import '../../providers/feed_provider.dart';
import 'widgets/comment_sheet.dart';
import 'widgets/feed_overlays.dart';
import 'widgets/feed_video_page.dart';

/// 首页 Feed：全屏竖向 PageView 沉浸式播放（《01-开发文档》5.2.1）
/// - 顶部：策略 Tab（推荐/最新/热度）+ 搜索入口
/// - 底部：游客/非会员免费剩余次数提示条
/// - 滑出暂停、滑入自动播放并上报观看计费
class FeedScreen extends ConsumerStatefulWidget {
  const FeedScreen({super.key});

  @override
  ConsumerState<FeedScreen> createState() => _FeedScreenState();
}

class _FeedScreenState extends ConsumerState<FeedScreen>
    with WidgetsBindingObserver {
  FeedStrategy _strategy = FeedStrategy.recommend;
  final PageController _pageController = PageController();
  StreamSubscription<FeedEvent>? _eventSub;

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
    // 登记当前策略，HomeShell 切回首页时只恢复这个策略的播放器池
    ref.read(activeFeedStrategyProvider.notifier).state = _strategy;
    // 监听计费/UI 事件（弹窗与 Toast 由 Notifier 事件流驱动）
    _eventSub = ref
        .read(feedProvider(_strategy).notifier)
        .events
        .listen(_handleEvent);
    // 从登录页等返回时恢复播放：provider 全局常驻保留了列表，
    // 但槽位已在 dispose 时 stopAll，需重新绑定（冷启动列表为空时为 no-op）
    WidgetsBinding.instance.addPostFrameCallback((_) {
      if (mounted) ref.read(feedProvider(_strategy).notifier).rebindCurrent();
    });
  }

  @override
  void dispose() {
    WidgetsBinding.instance.removeObserver(this);
    _eventSub?.cancel();
    // 离开 Feed 路由（如跳登录页）：彻底停止播放（断音+断缓存下载）。
    // feedProvider 是全局常驻，不处理则播放器池在后台继续出声
    ref.read(feedProvider(_strategy).notifier).pool.stopAll();
    _pageController.dispose();
    super.dispose();
  }

  /// App 退后台挂起、回前台从断点续播。inactive（下拉通知栏等瞬时态）
  /// 只轻量 pause 当前槽防出声；paused（真退后台）才走 suspend(stop)
  /// 彻底断下载——避免瞬时 inactive 触发 stop+重载的画面闪烁
  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    final notifier = ref.read(feedProvider(_strategy).notifier);
    if (state == AppLifecycleState.paused) {
      notifier.pool.suspend();
    } else if (state == AppLifecycleState.inactive) {
      notifier.pool.pauseCurrent();
    } else if (state == AppLifecycleState.resumed) {
      // 仅在首页 Tab 可见时恢复（在"我的"等页面回前台不播）
      if (ref.read(feedTabVisibleProvider)) {
        unawaited(() async {
          await notifier.pool.resume();
          await notifier.rebindCurrent();
        }());
      }
    }
  }

  void _handleEvent(FeedEvent event) {
    if (!mounted) return;
    switch (event) {
      case FeedToastEvent(:final message):
        showTopToast(context, message);
      case FeedGuestLimitEvent():
        showGuestLimitDialog(context);
      case FeedPointsInsufficientEvent(:final points):
        showPointsInsufficientDialog(context, points);
    }
  }

  void _switchStrategy(FeedStrategy next) {
    if (next == _strategy) return;
    // 挂起旧策略池（防在途 open 完成后自动出声）
    ref.read(feedProvider(_strategy).notifier).pool.suspend();
    setState(() => _strategy = next);
    ref.read(activeFeedStrategyProvider.notifier).state = next;
    _eventSub?.cancel();
    _eventSub = ref
        .read(feedProvider(_strategy).notifier)
        .events
        .listen(_handleEvent);
    _pageController.jumpToPage(0);
    // jumpToPage 后 resume + rebindCurrent：suspend 已 stop 槽位，仅 play
    // 播不起来，必须 rebind 重新 open（有断点记录则 seek 续播）
    WidgetsBinding.instance.addPostFrameCallback((_) {
      if (mounted) {
        unawaited(() async {
          final n = ref.read(feedProvider(_strategy).notifier);
          await n.pool.resume();
          await n.rebindCurrent();
        }());
      }
    });
  }

  /// 打开评论弹层：打开期间暂停当前播放，关闭后恢复
  Future<void> _openComments(VideoItem item) async {
    final notifier = ref.read(feedProvider(_strategy).notifier);
    notifier.pool.pauseCurrent();
    await showCommentSheet(
      context,
      videoId: item.videoId,
      onCountChanged: (delta) =>
          notifier.adjustCommentCount(item.videoId, delta),
    );
    if (mounted) notifier.pool.playCurrent();
  }

  @override
  Widget build(BuildContext context) {
    final state = ref.watch(feedProvider(_strategy));
    final notifier = ref.read(feedProvider(_strategy).notifier);

    return Scaffold(
      backgroundColor: Colors.black,
      body: Stack(
        children: [
          // 内容区
          if (state.isRefreshing && state.items.isEmpty)
            const Center(
              child: CircularProgressIndicator(color: AppColors.primary),
            )
          else if (state.loadFailed && state.items.isEmpty)
            _buildRetry(notifier)
          else if (state.items.isEmpty)
            const Center(
              child: Text('暂无视频', style: TextStyle(color: AppColors.textSecondary)),
            )
          else
            NotificationListener<ScrollNotification>(
              onNotification: (n) {
                // 手指开始拖动即静音，避免划动过程中上一个视频仍在出声
                if (n is ScrollStartNotification && n.dragDetails != null) {
                  notifier.pool.pauseCurrent();
                }
                return false;
              },
              child: PageView.builder(
                controller: _pageController,
                scrollDirection: Axis.vertical,
                itemCount: state.items.length,
                onPageChanged: notifier.onPageChanged,
                itemBuilder: (context, index) {
                  final item = state.items[index];
                  return FeedVideoPage(
                    key: ValueKey(item.videoId),
                    item: item,
                    slotIndex: notifier.pool.slotOf(index),
                    pool: notifier.pool,
                    isCurrent: index == state.currentIndex,
                    onLike: notifier.toggleLike,
                    onFavorite: notifier.toggleFavorite,
                    onComment: _openComments,
                    onReturnFromPlayer: notifier.rebindCurrent,
                  );
                },
              ),
            ),

          // 顶部：策略 Tab + 搜索入口
          SafeArea(
            child: Padding(
              padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 4),
              child: Row(
                children: [
                  const Spacer(),
                  for (final s in FeedStrategy.values) ...[
                    _StrategyTab(
                      label: s.label,
                      selected: s == _strategy,
                      onTap: () => _switchStrategy(s),
                    ),
                    const SizedBox(width: 16),
                  ],
                  IconButton(
                    icon: const Icon(Icons.search, color: Colors.white),
                    onPressed: () => context.push('/search'),
                  ),
                ],
              ),
            ),
          ),

          // 底部：免费剩余次数提示条（≤3 时显示）
          Positioned(
            left: 0,
            right: 0,
            bottom: 0,
            child: FreeQuotaBanner(remaining: state.freeRemainingToday),
          ),
        ],
      ),
    );
  }

  Widget _buildRetry(FeedNotifier notifier) {
    return Center(
      child: Column(
        mainAxisSize: MainAxisSize.min,
        children: [
          const Text('网络异常', style: TextStyle(color: AppColors.textSecondary)),
          const SizedBox(height: 12),
          TextButton(
            onPressed: notifier.refresh,
            child: const Text('点击重试', style: TextStyle(color: AppColors.primary)),
          ),
        ],
      ),
    );
  }
}

/// 顶部策略 Tab
class _StrategyTab extends StatelessWidget {
  const _StrategyTab({
    required this.label,
    required this.selected,
    required this.onTap,
  });

  final String label;
  final bool selected;
  final VoidCallback onTap;

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: onTap,
      child: Text(
        label,
        style: TextStyle(
          fontSize: 16,
          fontWeight: selected ? FontWeight.w700 : FontWeight.w400,
          color: selected ? Colors.white : AppColors.textSecondary,
          shadows: const [Shadow(color: Colors.black54, blurRadius: 4)],
        ),
      ),
    );
  }
}