feat(player): 增加进度条拖动画面预览
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Zhou Weidong committed
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// Author: fruit.com.cn
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import 'dart:async';
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import 'dart:collection';
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import 'package:flutter/foundation.dart';
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import 'package:flutter/services.dart';
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/// 原生取帧所需的播放源信息。
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class PlaybackThumbnailSource {
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const PlaybackThumbnailSource({
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this.localPath = '',
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this.remoteUrl = '',
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this.headers = const {},
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});
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final String localPath;
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final String remoteUrl;
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final Map<String, String> headers;
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bool get isAvailable => localPath.isNotEmpty || remoteUrl.isNotEmpty;
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}
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/// 按 episodeId 读取当前可用播放源，确保签名地址刷新后立即生效。
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typedef PlaybackThumbnailSourceResolver =
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PlaybackThumbnailSource? Function(String episodeId);
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/// 传给原生取帧层的单次请求。
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class PlaybackThumbnailFrameRequest {
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const PlaybackThumbnailFrameRequest({
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required this.episodeId,
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required this.position,
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required this.source,
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});
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final String episodeId;
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final Duration position;
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final PlaybackThumbnailSource source;
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Map<String, Object> toChannelArguments() => {
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'episodeId': episodeId,
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'timeMs': position.inMilliseconds,
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'localPath': source.localPath,
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'url': source.remoteUrl,
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'headers': source.headers,
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};
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}
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/// 可注入的原生取帧接口。
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abstract interface class PlaybackThumbnailFrameLoader {
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Future<ByteData?> load(PlaybackThumbnailFrameRequest request);
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void dispose();
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}
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/// 默认通过平台通道从本地播放器原生层取帧。
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class MethodChannelPlaybackThumbnailFrameLoader
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implements PlaybackThumbnailFrameLoader {
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MethodChannelPlaybackThumbnailFrameLoader({MethodChannel? channel})
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: _channel =
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channel ?? const MethodChannel('com.stormg.lumadrama/thumbnail');
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final MethodChannel _channel;
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@override
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Future<ByteData?> load(PlaybackThumbnailFrameRequest request) async {
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final bytes = await _channel.invokeMethod<Uint8List>(
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'frame',
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request.toChannelArguments(),
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);
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return bytes == null ? null : ByteData.sublistView(bytes);
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}
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@override
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void dispose() {}
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}
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/// 每秒一个 bucket，拖过同一秒时复用同一张缩略图。
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int playbackThumbnailBucket(Duration position) {
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final milliseconds = position.inMilliseconds;
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if (milliseconds <= 0) return 0;
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return milliseconds ~/ Duration.millisecondsPerSecond;
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}
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/// 播放器缩略图单飞、LRU 缓存与拖动预取调度。
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class PlaybackThumbnailService {
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PlaybackThumbnailService({
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PlaybackThumbnailFrameLoader? frameLoader,
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this.sourceResolver,
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this.requestTimeout = const Duration(milliseconds: 1500),
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this.prefetchDelay = const Duration(milliseconds: 120),
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this.cacheCapacity = defaultCacheCapacity,
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}) : _frameLoader =
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frameLoader ?? MethodChannelPlaybackThumbnailFrameLoader(),
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assert(cacheCapacity > 0);
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static const int defaultCacheCapacity = 24;
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final PlaybackThumbnailFrameLoader _frameLoader;
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final PlaybackThumbnailSourceResolver? sourceResolver;
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final Duration requestTimeout;
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final Duration prefetchDelay;
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final int cacheCapacity;
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final LinkedHashMap<String, ByteData> _cache = LinkedHashMap();
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final LinkedHashMap<String, bool> _unavailable = LinkedHashMap();
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_ThumbnailRequest? _inFlight;
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Future<ByteData?>? _inFlightFuture;
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_ThumbnailRequest? _queued;
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Timer? _prefetchTimer;
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String? _wantedKey;
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String? _latestEpisodeId;
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int? _latestBucket;
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int _prefetchDirection = 1;
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bool _disposed = false;
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@visibleForTesting
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int get cacheSize => _cache.length;
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/// 取指定剧集、时间点的缩略图。失败或超时统一返回 null。
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Future<ByteData?> thumbnail(String episodeId, Duration position) {
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if (_disposed) return Future<ByteData?>.value();
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final bucket = playbackThumbnailBucket(position);
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final key = _key(episodeId, bucket);
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_wantedKey = key;
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_noteRequestPosition(episodeId, bucket);
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_prefetchTimer?.cancel();
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_prefetchTimer = null;
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_dropQueued();
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final cached = _readCache(key);
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if (cached != null) {
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_schedulePrefetch(key);
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return Future<ByteData?>.value(cached);
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}
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if (_inFlight?.key == key && _inFlightFuture != null) {
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_schedulePrefetch(key);
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return _inFlightFuture!;
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}
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if (_unavailable.containsKey(key)) {
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_promoteUnavailable(key);
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_schedulePrefetch(key);
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return Future<ByteData?>.value();
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}
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final request = _ThumbnailRequest(
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key: key,
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episodeId: episodeId,
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bucket: bucket,
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);
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_schedulePrefetch(key);
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if (_inFlight == null) return _start(request);
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return _queue(request);
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}
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/// 松手或离开拖动后调用；只取消尚未开始的请求。
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void cancelPending() {
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_wantedKey = null;
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_prefetchTimer?.cancel();
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_prefetchTimer = null;
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_dropQueued();
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}
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/// 页面销毁时清空帧缓存和所有待执行请求。
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void clear() {
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cancelPending();
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_cache.clear();
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_unavailable.clear();
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_latestEpisodeId = null;
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_latestBucket = null;
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_prefetchDirection = 1;
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}
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void dispose() {
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if (_disposed) return;
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_disposed = true;
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clear();
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_frameLoader.dispose();
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}
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Future<ByteData?> _start(_ThumbnailRequest request) {
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final completer = Completer<ByteData?>();
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_inFlight = request;
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_inFlightFuture = completer.future;
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unawaited(_run(request, completer));
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return completer.future;
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}
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Future<ByteData?> _queue(_ThumbnailRequest request) {
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final completer = Completer<ByteData?>();
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_queued = request.withCompleter(completer);
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return completer.future;
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}
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Future<void> _run(
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_ThumbnailRequest request,
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Completer<ByteData?> completer,
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) async {
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ByteData? frame;
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try {
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frame = await _loadFrame(request);
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} catch (_) {
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frame = null;
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}
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if (frame == null) {
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_putUnavailable(request.key);
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} else {
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_putCache(request.key, frame);
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}
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final deliver = _wantedKey == request.key;
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_inFlight = null;
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_inFlightFuture = null;
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if (!completer.isCompleted) {
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completer.complete(deliver ? frame : null);
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}
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_drainQueued();
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}
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Future<ByteData?> _loadFrame(_ThumbnailRequest request) {
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PlaybackThumbnailSource? source;
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try {
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source = sourceResolver?.call(request.episodeId);
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} catch (_) {
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return Future<ByteData?>.value();
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}
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if (source == null || !source.isAvailable) {
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return Future<ByteData?>.value();
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}
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final frame = PlaybackThumbnailFrameRequest(
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episodeId: request.episodeId,
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position: Duration(seconds: request.bucket),
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source: source,
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);
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final result = Completer<ByteData?>();
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late final Timer timeout;
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void finish(ByteData? value) {
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if (result.isCompleted) return;
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timeout.cancel();
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result.complete(value);
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}
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timeout = Timer(requestTimeout, () => finish(null));
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try {
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_frameLoader
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.load(frame)
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.then(finish, onError: (Object _, StackTrace _) => finish(null));
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} catch (_) {
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finish(null);
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}
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return result.future;
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}
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void _drainQueued() {
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if (_disposed || _inFlight != null) return;
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final queued = _queued;
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_queued = null;
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if (queued == null || queued.key != _wantedKey) {
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queued?.completer.complete(null);
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return;
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}
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_inFlight = queued;
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_inFlightFuture = queued.completer.future;
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unawaited(_run(queued, queued.completer));
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}
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void _dropQueued() {
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final queued = _queued;
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_queued = null;
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if (queued != null && !queued.completer.isCompleted) {
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queued.completer.complete(null);
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}
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}
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void _noteRequestPosition(String episodeId, int bucket) {
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if (_latestEpisodeId == episodeId && _latestBucket != null) {
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if (bucket < _latestBucket!) _prefetchDirection = -1;
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if (bucket > _latestBucket!) _prefetchDirection = 1;
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}
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_latestEpisodeId = episodeId;
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_latestBucket = bucket;
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}
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void _schedulePrefetch(String currentKey) {
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_prefetchTimer?.cancel();
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_prefetchTimer = Timer(prefetchDelay, () {
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_prefetchTimer = null;
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if (_disposed || _wantedKey != currentKey) return;
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final episodeId = _latestEpisodeId;
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final bucket = _latestBucket;
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if (episodeId == null || bucket == null) return;
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final neighbor = bucket + _prefetchDirection;
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if (neighbor < 0) return;
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final key = _key(episodeId, neighbor);
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if (_cache.containsKey(key) ||
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_unavailable.containsKey(key) ||
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_inFlight?.key == key ||
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_queued != null) {
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return;
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}
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final request = _ThumbnailRequest(
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key: key,
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episodeId: episodeId,
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bucket: neighbor,
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);
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if (_inFlight == null) {
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unawaited(_start(request));
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} else {
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_queue(request);
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}
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});
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}
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ByteData? _readCache(String key) {
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final value = _cache.remove(key);
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if (value == null) return null;
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_cache[key] = value;
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return value;
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}
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void _putCache(String key, ByteData value) {
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_unavailable.remove(key);
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_cache.remove(key);
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_cache[key] = value;
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while (_cache.length > cacheCapacity) {
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_cache.remove(_cache.keys.first);
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}
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}
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void _putUnavailable(String key) {
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_unavailable.remove(key);
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_unavailable[key] = true;
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while (_unavailable.length > cacheCapacity) {
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_unavailable.remove(_unavailable.keys.first);
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}
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}
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void _promoteUnavailable(String key) {
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if (_unavailable.remove(key) == null) return;
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_unavailable[key] = true;
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}
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String _key(String episodeId, int bucket) => '$episodeId:$bucket';
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}
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class _ThumbnailRequest {
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_ThumbnailRequest({
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required this.key,
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required this.episodeId,
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required this.bucket,
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Completer<ByteData?>? completer,
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}) : completer = completer ?? Completer<ByteData?>();
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final String key;
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final String episodeId;
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final int bucket;
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final Completer<ByteData?> completer;
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_ThumbnailRequest withCompleter(Completer<ByteData?> value) =>
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_ThumbnailRequest(
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key: key,
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episodeId: episodeId,
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bucket: bucket,
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completer: value,
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);
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}
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