// lib/pages/playlist_page.dart
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import '../services/audio_service.dart';

class PlaylistPage extends StatefulWidget {
  const PlaylistPage({super.key});

  @override
  State<PlaylistPage> createState() => _PlaylistPageState();
}

class _PlaylistPageState extends State<PlaylistPage> {
  final ScrollController _scrollController = ScrollController();
  final GlobalKey _currentTagKey = GlobalKey();

  // ⭐ 定位事务 ID（防止旧任务污染）
  int _scrollGeneration = 0;

  // ⭐ 是否已完成定位
  bool _hasScrolledToCurrent = false;

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addPostFrameCallback((_) {
      _scrollToCurrentSong();
    });
  }

  @override
  void dispose() {
    _scrollController.dispose();
    super.dispose();
  }

  /// ⭐ 核心：一次计算 + 一次动画
  Future<void> _scrollToCurrentSong() async {
    if (_hasScrolledToCurrent) return;

    final service = context.read<AudioService>();
    final queue = service.queue;
    final currentIndex = service.currentIndex;

    if (queue.isEmpty || currentIndex < 0 || currentIndex >= queue.length) {
      return;
    }

    // 生成新的事务 ID，使旧任务失效
    final generation = ++_scrollGeneration;

    // 等待页面稳定
    await Future.delayed(const Duration(milliseconds: 300));
    if (!mounted || generation != _scrollGeneration) return;

    // 获取目标 item 的当前布局状态
    var tagContext = _currentTagKey.currentContext;

    // ⭐ 如果 Tag 还没被构建，用不可见的 jumpTo 触发布局
    if (tagContext == null) {
      // 用 maxExtent 计算平均高度，做一次瞬时定位
      final maxExtent = _scrollController.position.maxScrollExtent;
      final avgHeight = maxExtent / queue.length;
      final viewportHeight = _scrollController.position.viewportDimension;
      final roughOffset =
          (currentIndex * avgHeight) - (viewportHeight / 2) + (avgHeight / 2);
      final clamped = roughOffset.clamp(0.0, maxExtent);

      // ⭐ 瞬时跳转（用户不可见）
      _scrollController.jumpTo(clamped);

      // 等待一帧，让目标 item 被构建
      await WidgetsBinding.instance.endOfFrame;
      if (!mounted || generation != _scrollGeneration) return;

      tagContext = _currentTagKey.currentContext;

      // 如果还是 null，说明估算偏差太大，用迭代方式推进
      if (tagContext == null) {
        // 最多尝试 2 次，每次推进半屏
        for (int i = 0; i < 2; i++) {
          final viewportHeight2 = _scrollController.position.viewportDimension;
          final direction = (currentIndex > queue.length / 2) ? -1 : 1;
          final step = viewportHeight2 * 0.7 * direction;
          final newOffset = (_scrollController.offset + step)
              .clamp(0.0, _scrollController.position.maxScrollExtent);
          _scrollController.jumpTo(newOffset);
          await WidgetsBinding.instance.endOfFrame;
          if (!mounted || generation != _scrollGeneration) return;
          tagContext = _currentTagKey.currentContext;
          if (tagContext != null) break;
        }
        if (tagContext == null) {
          _hasScrolledToCurrent = true;
          return;
        }
      }
    }

    if (!mounted || generation != _scrollGeneration) return;

    // ⭐ 获取 Tag 的真实位置
    final renderBox = tagContext!.findRenderObject() as RenderBox?;
    if (renderBox == null) {
      _hasScrolledToCurrent = true;
      return;
    }

    final tagPosition = renderBox.localToGlobal(Offset.zero);
    final tagSize = renderBox.size;
    final tagCenter = tagPosition.dy + tagSize.height / 2;

    final screenHeight = MediaQuery.of(context).size.height;
    final screenCenter = screenHeight / 2;

    final delta = tagCenter - screenCenter;
    final currentOffset = _scrollController.offset;
    final targetOffset = (currentOffset + delta)
        .clamp(0.0, _scrollController.position.maxScrollExtent);

    // 如果偏差太小，直接标记完成
    if ((targetOffset - currentOffset).abs() < 5) {
      _hasScrolledToCurrent = true;
      return;
    }

    // ⭐ 根据距离动态计算时长
    final distance = (targetOffset - currentOffset).abs();
    final durationMs = (250 + distance * 0.3).clamp(250, 700).round();
    final duration = Duration(milliseconds: durationMs);

    debugPrint(
        '🎯 [定位] 距离: ${distance.toStringAsFixed(0)}px, 时长: ${durationMs}ms');

    // ⭐ 唯一的一次可见动画
    await _scrollController.animateTo(
      targetOffset,
      duration: duration,
      curve: Curves.easeOutCubic,
    );

    if (mounted && generation == _scrollGeneration) {
      _hasScrolledToCurrent = true;
    }
  }

  @override
  Widget build(BuildContext context) {
    final service = context.watch<AudioService>();
    final queue = service.queue;
    final currentIndex = service.currentIndex;

    return Scaffold(
      backgroundColor: const Color(0xFF0E1211),
      appBar: AppBar(
        title: const Text(
          '播放列表',
          style: TextStyle(
            color: Colors.white,
            fontSize: 18,
            fontWeight: FontWeight.w500,
          ),
        ),
        backgroundColor: Colors.transparent,
        elevation: 0,
        foregroundColor: Colors.white,
        leading: IconButton(
          icon: const Icon(Icons.arrow_back_ios_new),
          onPressed: () => Navigator.pop(context),
        ),
        actions: [
          IconButton(
            icon: Icon(service.playModeIcon, color: Colors.white54),
            onPressed: service.togglePlayMode,
          ),
          IconButton(
            icon: const Icon(Icons.clear_all, color: Colors.white54),
            onPressed: () {
              showDialog(
                context: context,
                builder: (context) => AlertDialog(
                  backgroundColor: const Color(0xFF1A1F1E),
                  title: const Text('清空播放列表',
                      style: TextStyle(color: Colors.white)),
                  content: const Text('确定要清空当前播放列表吗？',
                      style: TextStyle(color: Colors.grey)),
                  actions: [
                    TextButton(
                        onPressed: () => Navigator.pop(context),
                        child: const Text('取消')),
                    TextButton(
                      onPressed: () {
                        service.clearQueue();
                        Navigator.pop(context);
                        Navigator.pop(context);
                      },
                      child:
                          const Text('清空', style: TextStyle(color: Colors.red)),
                    ),
                  ],
                ),
              );
            },
          ),
        ],
      ),
      body: queue.isEmpty
          ? const Center(
              child: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: [
                  Icon(Icons.playlist_play, size: 48, color: Colors.grey),
                  SizedBox(height: 16),
                  Text('播放列表为空', style: TextStyle(color: Colors.grey)),
                ],
              ),
            )
          : ListView.builder(
              controller: _scrollController,
              padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
              itemCount: queue.length,
              itemBuilder: (context, index) {
                final song = queue[index];
                final isCurrent = index == currentIndex;

                return ListTile(
                  contentPadding: const EdgeInsets.symmetric(
                    horizontal: 8,
                    vertical: 4,
                  ),
                  leading: Icon(
                    isCurrent ? Icons.play_arrow : Icons.music_note,
                    color:
                        isCurrent ? const Color(0xFFB8D4D0) : Colors.grey[600],
                    size: 24,
                  ),
                  title: Text(
                    song.title,
                    style: TextStyle(
                      fontSize: 16,
                      fontWeight: isCurrent ? FontWeight.w600 : FontWeight.w400,
                      color: isCurrent ? Colors.white : Colors.grey[300],
                    ),
                    maxLines: 1,
                    overflow: TextOverflow.ellipsis,
                  ),
                  subtitle: Text(
                    song.artist,
                    style: TextStyle(
                      fontSize: 13,
                      color: isCurrent ? Colors.grey[400] : Colors.grey[600],
                    ),
                    maxLines: 1,
                    overflow: TextOverflow.ellipsis,
                  ),
                  trailing: isCurrent
                      ? Container(
                          key: _currentTagKey,
                          padding: const EdgeInsets.symmetric(
                            horizontal: 8,
                            vertical: 2,
                          ),
                          decoration: BoxDecoration(
                            color:
                                const Color(0xFFB8D4D0).withValues(alpha: 0.2),
                            borderRadius: BorderRadius.circular(4),
                          ),
                          child: const Text(
                            '正在播放',
                            style: TextStyle(
                              fontSize: 10,
                              color: Color(0xFFB8D4D0),
                            ),
                          ),
                        )
                      : null,
                  onTap: () {
                    service.setQueue(queue, startIndex: index);
                    Navigator.pop(context);
                  },
                );
              },
            ),
    );
  }
}