ReelShort/lib/pages/player/widgets/player_opening_frame.dart

// Author: fruit.com.cn

import 'dart:async';
import 'dart:ui' as ui;

import 'package:flutter/material.dart';

import '../../../core/config/app_config.dart';
import '../../../core/data/services/sprite_thumbnail_asset_loader.dart';
import '../../../core/data/services/sprite_thumbnail_axis.dart';
import 'scrub_preview_card.dart';

/// 无雪碧图地址时不垫帧，交还给纯黑底。
Widget? playerOpeningFrame(String? thumbnailsUrl) {
  final url = thumbnailsUrl?.trim() ?? '';
  if (url.isEmpty) return null;
  return PlayerOpeningFrame(thumbnailsUrl: url);
}

/// 解码出视频画面前，用本集雪碧图第一帧垫底。
class PlayerOpeningFrame extends StatefulWidget {
  const PlayerOpeningFrame({
    super.key,
    required this.thumbnailsUrl,
    this.loader,
    this.cache,
  });

  final String thumbnailsUrl;
  final SpriteThumbnailAssetLoader? loader;
  final OpeningFrameCache? cache;

  @override
  State<PlayerOpeningFrame> createState() => _PlayerOpeningFrameState();
}

class _PlayerOpeningFrameState extends State<PlayerOpeningFrame> {
  SpriteThumbnailFrame? _frame;
  int _serial = 0;

  @override
  void initState() {
    super.initState();
    unawaited(_load());
  }

  @override
  void didUpdateWidget(covariant PlayerOpeningFrame oldWidget) {
    super.didUpdateWidget(oldWidget);
    if (oldWidget.thumbnailsUrl != widget.thumbnailsUrl) {
      _frame = null;
      unawaited(_load());
    }
  }

  Future<void> _load() async {
    final serial = ++_serial;
    final frame = await (widget.cache ?? OpeningFrameCache.shared).load(
      widget.thumbnailsUrl,
      loader: widget.loader,
    );
    if (!mounted || serial != _serial) return;
    setState(() => _frame = frame);
  }

  @override
  Widget build(BuildContext context) {
    final frame = _frame;
    if (frame == null) return const SizedBox.expand();
    return SpriteCropPreview(
      key: const Key('player-opening-sprite'),
      image: frame.image,
      sourceRect: frame.sourceRect,
    );
  }
}

/// 相邻页共用的雪碧图首帧缓存，避免每页重复拉 VTT。
class OpeningFrameCache {
  OpeningFrameCache({this.capacity = 6});

  static final OpeningFrameCache shared = OpeningFrameCache();

  final int capacity;
  final Map<String, SpriteThumbnailFrame> _frames = {};
  final Map<String, Future<SpriteThumbnailFrame?>> _loads = {};

  /// 取 [thumbnailsUrl] 对应的第一帧；失败返回 null。
  Future<SpriteThumbnailFrame?> load(
    String? thumbnailsUrl, {
    SpriteThumbnailAssetLoader? loader,
  }) {
    final url = _normalize(thumbnailsUrl);
    if (url == null) return Future<SpriteThumbnailFrame?>.value();
    final cached = _frames[url];
    if (cached != null) return Future.value(cached);
    return _loads.putIfAbsent(url, () => _fetch(url, loader));
  }

  Future<SpriteThumbnailFrame?> _fetch(
    String url,
    SpriteThumbnailAssetLoader? loader,
  ) async {
    try {
      final asset = loader ?? DioSpriteThumbnailAssetLoader();
      final text = await asset.loadVtt(Uri.parse(url));
      if (text == null || text.isEmpty) return null;
      final axis = parseSpriteThumbnailVtt(text, vttUrl: url);
      final cue = axis.cues.isEmpty ? null : axis.cues.first;
      if (cue == null) return null;
      final decoded = await asset.loadSprite(
        axis.resolveSpriteUri(cue.spriteFile),
      );
      if (decoded == null) return null;
      final frame = SpriteThumbnailFrame(
        image: decoded.image,
        sourceRect: _scaledRect(decoded, cue.sourceRect),
        spriteUrl: axis.resolveSpriteUri(cue.spriteFile).toString(),
        cue: cue,
      );
      _store(url, frame);
      return frame;
    } catch (_) {
      return null;
    } finally {
      _loads.remove(url);
    }
  }

  void _store(String url, SpriteThumbnailFrame frame) {
    _frames.remove(url);
    _frames[url] = frame;
    while (_frames.length > capacity) {
      final oldest = _frames.keys.first;
      _frames.remove(oldest)?.image.dispose();
    }
  }

  ui.Rect _scaledRect(SpriteThumbnailDecodedImage decoded, ui.Rect source) {
    if (decoded.originalWidth <= 0 || decoded.originalHeight <= 0) {
      return source;
    }
    final scaleX = decoded.image.width / decoded.originalWidth;
    final scaleY = decoded.image.height / decoded.originalHeight;
    return ui.Rect.fromLTWH(
      source.left * scaleX,
      source.top * scaleY,
      source.width * scaleX,
      source.height * scaleY,
    );
  }

  String? _normalize(String? raw) {
    final value = AppConfig.mediaUrl(raw?.trim() ?? '');
    if (value.isEmpty) return null;
    return value;
  }

  /// 测试收尾时清空缓存。
  void clear() {
    for (final frame in _frames.values) {
      frame.image.dispose();
    }
    _frames.clear();
    _loads.clear();
  }
}