fixed some bugs

ios/OralTrainer/Player/PlayerController.swift

@@ -20,12 +20,18 @@ final class PlayerController: ObservableObject {
     private var lastSentenceIndex: Int?
     private var pendingSeekPositionMs: Int64?
     private var seekGeneration = 0
+    /// ExoPlayer 的 playWhenReady 等价物。AVPlayer 的 actionAtItemEnd 可能在
+    /// 句尾和切句 seek 的极短竞态里先自动暂停；这里不能依赖 player.rate 判断
+    /// 用户是否希望继续播放。
+    private var playbackIntent = false
     private var stopAtSentenceEnd = false
     private var stopAtSentenceEndIndex: Int?
     private var swipeBackAnchorIndex: Int?
     private var swipeBackAnchorTime: TimeInterval = 0
     private var speedBeforeLongPress: Float?
     private var transientTask: Task<Void, Never>?
+    private var cacheSwapTask: Task<Void, Never>?
+    private var activePlaybackURL: URL?
     private var sentenceEndTimeObserver: Any?
     private var sentenceEndGuardToken = 0
 
@@ -79,6 +85,7 @@ final class PlayerController: ObservableObject {
 
     // MARK: - 装载
 
+    @MainActor
     func load(_ item: TrainingMediaItem) {
         cancelSentenceBoundaryGuard()
         lastSentenceIndex = nil
@@ -89,18 +96,51 @@ final class PlayerController: ObservableObject {
         mediaItem = item
         currentItem = item
         boundaryState = .idle
-        let playerItem = AVPlayerItem(url: item.url)
+        let playbackURL: URL
+        if item.isLocalFile {
+            playbackURL = item.url
+        } else if let cachedURL = StreamingVideoCache.shared.cachedFileIfAvailable(for: item.url) {
+            playbackURL = cachedURL
+        } else {
+            playbackURL = item.url
+        }
+
+        activePlaybackURL = playbackURL
+        let playerItem = AVPlayerItem(url: playbackURL)
         attachItemObservers(to: playerItem)
         player.replaceCurrentItem(with: playerItem)
         if config.autoPlay {
             player.play()
         }
+        playbackIntent = config.autoPlay
+        scheduleCachePrefetchIfNeeded(for: item, activeURL: playbackURL)
+        tick()
+    }
+
+    /// 句边界请求完成后只更新训练数据，不重新创建 AVPlayerItem。
+    /// 否则会把 AVFoundation 已经缓存的媒体数据丢掉，回跳上一句时可能重新联网。
+    @MainActor
+    func updateBoundaries(_ sentences: [SentenceBoundary]) {
+        guard let oldItem = mediaItem else {
+            return
+        }
+        let newItem = TrainingMediaItem(
+            id: oldItem.id,
+            title: oldItem.title,
+            url: oldItem.url,
+            sentences: sentences,
+            isLocalFile: oldItem.isLocalFile
+        )
+        mediaItem = newItem
+        currentItem = newItem
+        lastSentenceIndex = nil
         tick()
     }
 
     // MARK: - 播放控制
 
     func play() {
+        playbackIntent = true
         player.play()
         // play() 可能在 AVPlayer 还没有把 timeControlStatus 切到 playing 前被调用；
         // 立即强制注册一次，避免最初的几十毫秒没有被句尾守卫覆盖。
@@ -110,6 +150,7 @@ final class PlayerController: ObservableObject {
     func pause() {
         stopAtSentenceEnd = false
         stopAtSentenceEndIndex = nil
+        playbackIntent = false
         cancelSentenceBoundaryGuard()
         player.pause()
     }
@@ -129,6 +170,7 @@ final class PlayerController: ObservableObject {
     func stop() {
         stopAtSentenceEnd = false
         stopAtSentenceEndIndex = nil
+        playbackIntent = false
         cancelSentenceBoundaryGuard()
         player.pause()
         seek(to: .zero)
@@ -423,10 +465,52 @@ final class PlayerController: ObservableObject {
         pendingSeekPositionMs ?? currentPositionMs()
     }
 
+    @MainActor
+    private func scheduleCachePrefetchIfNeeded(for item: TrainingMediaItem, activeURL: URL) {
+        cacheSwapTask?.cancel()
+        cacheSwapTask = nil
+        guard !item.isLocalFile,
+              activeURL != item.url else {
+            return
+        }
+
+        let remoteURL = item.url
+        cacheSwapTask = Task { [weak self] in
+            guard let cachedURL = await StreamingVideoCache.shared.prefetch(remoteURL) else {
+                return
+            }
+            self?.swapToCachedFileIfNeeded(remoteURL: remoteURL, cachedURL: cachedURL)
+        }
+    }
+
+    @MainActor
+    private func swapToCachedFileIfNeeded(remoteURL: URL, cachedURL: URL) {
+        guard !Task.isCancelled,
+              mediaItem?.url == remoteURL,
+	              activePlaybackURL != cachedURL else {
+            return
+        }
+
+        let targetPositionMs = pendingSeekPositionMs ?? currentPositionMs()
+        let newItem = AVPlayerItem(url: cachedURL)
+        activePlaybackURL = cachedURL
+
+        // 递增 seek generation，让旧远程 Item 上未完成的 seek 回调失效。
+        seekGeneration += 1
+        attachItemObservers(to: newItem)
+        player.replaceCurrentItem(with: newItem)
+        performSeek(to: targetPositionMs)
+    }
+
     /// AVPlayer 的 seek 是异步的；所有 seek 必须统一走这里，避免播放循环、
     /// 用户手势和 seek 完成回调交错后把位置拉回旧句子。
-    private func performSeek(to positionMs: Int64, completion: (() -> Void)? = nil) {
+    private func performSeek(
+        to positionMs: Int64,
+        resumePlayback: Bool? = nil,
+        completion: (() -> Void)? = nil
+    ) {
         let targetPositionMs = max(0, positionMs)
+        let shouldResumePlayback = resumePlayback ?? playbackIntent
         seekGeneration += 1
         let generation = seekGeneration
         pendingSeekPositionMs = targetPositionMs
@@ -441,6 +525,9 @@ final class PlayerController: ObservableObject {
                 }
                 self.pendingSeekPositionMs = nil
                 self.tick()
+                if shouldResumePlayback {
+                    self.player.play()
+                }
                 completion?()
             }
         }
@@ -628,6 +715,7 @@ final class PlayerController: ObservableObject {
         if stopAtSentenceEnd, stopAtSentenceEndIndex == sentence.index {
             stopAtSentenceEnd = false
             stopAtSentenceEndIndex = nil
+            playbackIntent = false
             player.pause()
             seekRaw(sentenceSeekPosition(sentence))
             tick()
@@ -687,8 +775,9 @@ final class PlayerController: ObservableObject {
             tick()
             return
         }
+        // 播放中自然结束时 playbackIntent 仍为 true；如果用户本来已暂停，
+        // 则不应因为到达 media end 而突然自动循环。
         performSeek(to: .zero)
-        player.play()
         tick()
     }