fixed some bugs

ios/OralTrainer/Player/PlayerController.swift

@@ -22,9 +22,16 @@ final class PlayerController: ObservableObject {
     private var seekGeneration = 0
     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 static let swipeBackPhaseTimeout: TimeInterval = 1.2
+    /// AVPlayer 在个别句子边界会把 seek 结果上报得比目标早 1ms 左右。
+    /// 如果恰好落在句边界前，tick 会把句子重新判定回上一句；稍微进入目标句可消除该问题。
+    private static let sentenceSeekInsetMs: Int64 = 20
+
     private var timeObserver: Any?
     private var endObserver: NSObjectProtocol?
     private var itemStatusObserver: NSKeyValueObservation?
@@ -69,6 +76,7 @@ final class PlayerController: ObservableObject {
 
     func load(_ item: TrainingMediaItem) {
         lastSentenceIndex = nil
+        swipeBackAnchorIndex = nil
         pendingSeekPositionMs = nil
         stopAtSentenceEnd = false
         stopAtSentenceEndIndex = nil
@@ -140,12 +148,9 @@ final class PlayerController: ObservableObject {
         guard let item = mediaItem, !item.sentences.isEmpty else {
             return false
         }
-        let position = referencePositionMs()
-        guard let target = item.sentences.reversed().first(where: { $0.startMs < position - 250 })
-            ?? item.sentences.first else {
-            return false
-        }
-        seek(to: target.startMs)
+        guard let currentIndex = sentenceAnchorIndex() else { return false }
+        let target = item.sentences[max(0, currentIndex - 1)]
+        seekToSentenceBeginning(target)
         return true
     }
 
@@ -154,14 +159,47 @@ final class PlayerController: ObservableObject {
         guard let item = mediaItem, !item.sentences.isEmpty else {
             return false
         }
-        let position = referencePositionMs()
-        guard let target = item.sentences.first(where: { $0.startMs > position + 150 }) else {
+        guard let currentIndex = sentenceAnchorIndex() else { return false }
+        let targetIndex = currentIndex + 1
+        guard item.sentences.indices.contains(targetIndex) else {
             return false
         }
-        seek(to: target.startMs)
+        let target = item.sentences[targetIndex]
+        seekToSentenceBeginning(target)
         return true
     }
 
+    /// 按索引跳转，而不是每次用异步的 AVPlayer 时间重新搜索。
+    /// 这样一次手势只前进/后退一句，也不会因 seek 后时间上报偏差导致重复或无效。
+    @discardableResult
+    func seekToSentence(at index: Int) -> Bool {
+        guard let item = mediaItem, item.sentences.indices.contains(index) else {
+            return false
+        }
+        seekToSentenceBeginning(item.sentences[index])
+        return true
+    }
+
+    private func sentenceAnchorIndex() -> Int? {
+        guard let item = mediaItem, !item.sentences.isEmpty else { return nil }
+        if let index = currentSentence?.index, item.sentences.indices.contains(index) {
+            return index
+        }
+        if let index = lastSentenceIndex, item.sentences.indices.contains(index) {
+            return index
+        }
+
+        let position = referencePositionMs()
+        if let sentence = sentence(at: position) {
+            return sentence.index
+        }
+        // 句间隙中时，取前一句作为锚点；在第一句之前时取下一句。
+        if let previous = item.sentences.last(where: { $0.startMs <= position }) {
+            return previous.index
+        }
+        return item.sentences.first?.index
+    }
+
     func previousSentenceOrRewind() {
         if !config.sentenceMode || !seekToPreviousSentence() {
             rewind()
@@ -174,12 +212,55 @@ final class PlayerController: ObservableObject {
         }
     }
 
+    /// 播放中向左划：第一次回到当前句开头重播；短时间内再划一次才到上一句。
+    /// 暂停时保持原来的“上一句”语义，测试页“上一句”按钮也不受影响。
+    @discardableResult
+    func replayOrPreviousSentence() -> SwipeBackResult {
+        guard config.sentenceMode,
+              let item = mediaItem,
+              !item.sentences.isEmpty,
+              let anchorIndex = sentenceAnchorIndex() else {
+            rewind()
+            return .rewound
+        }
+
+        let isActivelyPlaying = player.timeControlStatus == .playing
+            || player.timeControlStatus == .waitingToPlayAtSpecifiedRate
+        guard isActivelyPlaying else {
+            swipeBackAnchorIndex = nil
+            return seekToPreviousSentence() ? .movedPrevious : .stayedAtFirst
+        }
+
+        let now = Date().timeIntervalSinceReferenceDate
+        if swipeBackAnchorIndex == anchorIndex,
+           now - swipeBackAnchorTime <= Self.swipeBackPhaseTimeout {
+            swipeBackAnchorIndex = nil
+            guard anchorIndex > 0 else {
+                seekToSentenceBeginning(item.sentences[anchorIndex])
+                return .stayedAtFirst
+            }
+            seekToSentenceBeginning(item.sentences[anchorIndex - 1])
+            return .movedPrevious
+        }
+
+        swipeBackAnchorIndex = anchorIndex
+        swipeBackAnchorTime = now
+        let current = item.sentences[anchorIndex]
+        if stopAtSentenceEnd {
+            playCurrentSentenceAndStop()
+        } else {
+            seekToSentenceBeginning(current)
+            play()
+        }
+        return .restartedCurrent
+    }
+
     /// 只播放当前句子，播完自动暂停并回到句首（评测“播放原句”）。
     func playCurrentSentenceAndStop() {
         guard let sentence = currentSentence else {
             return
         }
-        performSeek(to: sentence.startMs)
+        performSeek(to: sentenceSeekPosition(sentence))
         stopAtSentenceEnd = true
         stopAtSentenceEndIndex = sentence.index
         play()
@@ -249,8 +330,16 @@ final class PlayerController: ObservableObject {
             togglePlayPause()
             showTransientMessage("播放状态已切换")
         case .swipeLeft:
-            previousSentenceOrRewind()
-            showTransientMessage("已跳到上一句")
+            switch replayOrPreviousSentence() {
+            case .restartedCurrent:
+                showTransientMessage("已回到本句开头，再左划返回上一句")
+            case .movedPrevious:
+                showTransientMessage("已跳到上一句")
+            case .stayedAtFirst:
+                showTransientMessage("已是第一句")
+            case .rewound:
+                showTransientMessage("已快退")
+            }
         case .swipeRight:
             nextSentenceOrForward()
             showTransientMessage("已跳到下一句")
@@ -290,6 +379,9 @@ final class PlayerController: ObservableObject {
         if sentence?.index != lastSentenceIndex {
             lastSentenceIndex = sentence?.index
         }
+        if sentence?.index != swipeBackAnchorIndex {
+            swipeBackAnchorIndex = nil
+        }
         let duration = durationMs(of: item)
         let state = playbackState(of: item, positionMs: finalPosition, durationMs: duration)
         snapshot = PlaybackSnapshot(
@@ -422,7 +514,7 @@ final class PlayerController: ObservableObject {
             return
         }
         if positionMs >= anchor.endMs {
-            seekRaw(anchor.startMs)
+            seekRaw(sentenceSeekPosition(anchor))
         }
     }
 
@@ -430,6 +522,16 @@ final class PlayerController: ObservableObject {
         performSeek(to: positionMs)
     }
 
+    private func sentenceSeekPosition(_ sentence: SentenceBoundary) -> Int64 {
+        let available = max(0, sentence.endMs - sentence.startMs - 1)
+        let inset = min(Self.sentenceSeekInsetMs, available)
+        return sentence.startMs + inset
+    }
+
+    private func seekToSentenceBeginning(_ sentence: SentenceBoundary) {
+        seek(to: sentenceSeekPosition(sentence))
+    }
+
     private func handleEnded() {
         guard loopMode != .off else {
             tick()