Handle multi-track files for sleep timer

ios/App/Shared/models/server/AudioTrack.swift

@@ -19,6 +19,13 @@ class AudioTrack: EmbeddedObject, Codable {
     @Persisted var localFileId: String?
     @Persisted var serverIndex: Int?
     
+    var endOffset: Double? {
+        if let startOffset = startOffset {
+            return startOffset + duration
+        }
+        return nil
+    }
+    
     private enum CodingKeys : String, CodingKey {
         case index, startOffset, duration, title, contentUrl, mimeType, metadata, localFileId, serverIndex
     }

ios/App/Shared/player/AudioPlayer.swift

@@ -45,7 +45,7 @@ class AudioPlayer: NSObject {
     internal var sleepTimer: Timer?
     internal var sleepTimeRemaining: Double?
     
-    private var currentTrackIndex = 0
+    internal var currentTrackIndex = 0
     private var allPlayerItems:[AVPlayerItem] = []
     
     private var pausedTimer: Timer?

ios/App/Shared/player/AudioPlayerSleepTimer.swift

@@ -22,7 +22,7 @@ extension AudioPlayer {
         // Return the player time until sleep
         var sleepTimeRemaining: Double? = nil
         if let chapterStopAt = self.sleepTimeChapterStopAt {
-            sleepTimeRemaining = chapterStopAt - currentTime
+            sleepTimeRemaining = (chapterStopAt - currentTime) / Double(self.rate > 0 ? self.rate : 1.0)
         } else if self.isCountdownSleepTimerSet() {
             sleepTimeRemaining = self.sleepTimeRemaining
         }
@@ -59,7 +59,22 @@ extension AudioPlayer {
         
         // Schedule the observation time
         self.sleepTimeChapterStopAt = stopAt
-        let sleepTime = CMTime(seconds: stopAt, preferredTimescale: CMTimeScale(NSEC_PER_SEC))
+        
+        // Get the current track
+        guard let playbackSession = self.getPlaybackSession() else { return }
+        let currentTrack = playbackSession.audioTracks[currentTrackIndex]
+
+        // Set values
+        guard let trackStartTime = currentTrack.startOffset else { return }
+        guard let trackEndTime = currentTrack.endOffset else { return }
+
+        // Verify the stop is during the current audio track
+        guard trackEndTime >= stopAt else { return }
+
+        // Schedule the observation time
+        let trackBasedStopTime = stopAt - trackStartTime
+        
+        let sleepTime = CMTime(seconds: trackBasedStopTime, preferredTimescale: CMTimeScale(NSEC_PER_SEC))
         var times = [NSValue]()
         times.append(NSValue(time: sleepTime))