Fix track subscribe (#20)

* fixed

* format

* set track to null

* rearrange

lib/src/rtc_engine.dart

@@ -337,6 +337,8 @@ class RTCEngine extends Disposable with EventsEmittable<EngineEvent> {
     });
 
     subscriber?.pc.onTrack = (rtc.RTCTrackEvent event) {
+      logger.fine('[WebRTC] pc.onTrack');
+
       final stream = event.streams.firstOrNull;
       if (stream == null) {
         // we need the stream to get the track's id
@@ -344,6 +346,16 @@ class RTCEngine extends Disposable with EventsEmittable<EngineEvent> {
         return;
       }
 
+      // doesn't get called reliably
+      event.track.onEnded = () {
+        logger.fine('[WebRTC] track.onEnded');
+      };
+
+      // doesn't get called reliably
+      stream.onRemoveTrack = (_) {
+        logger.fine('[WebRTC] stream.onRemoveTrack');
+      };
+
       events.emit(EngineTrackAddedEvent(
         track: event.track,
         stream: stream,
@@ -351,6 +363,12 @@ class RTCEngine extends Disposable with EventsEmittable<EngineEvent> {
       ));
     };
 
+    // doesn't get called reliably, doesn't work on mac
+    subscriber?.pc.onRemoveTrack =
+        (rtc.MediaStream stream, rtc.MediaStreamTrack track) {
+      logger.fine('[WebRTC] ${track.id} pc.onRemoveTrack');
+    };
+
     // also handle messages over the pub channel, for backwards compatibility
     try {
       final lossyInit = rtc.RTCDataChannelInit()

lib/src/track/remote_track_publication.dart

@@ -1,3 +1,5 @@
+import 'package:livekit_client/src/logger.dart';
+
 import '../events.dart';
 import '../extensions.dart';
 import '../participant/remote_participant.dart';
@@ -10,10 +12,8 @@ import 'track_publication.dart';
 /// control if we should subscribe to the track, and its quality (for video).
 class RemoteTrackPublication extends TrackPublication {
   final RemoteParticipant _participant;
-  bool _unsubscribed = false;
   bool _disabled = false;
   lk_rtc.VideoQuality _videoQuality = lk_rtc.VideoQuality.HIGH;
-
   lk_rtc.VideoQuality get videoQuality => _videoQuality;
 
   set videoQuality(lk_rtc.VideoQuality val) {
@@ -29,18 +29,23 @@ class RemoteTrackPublication extends TrackPublication {
     _sendUpdateTrackSettings();
   }
 
-  @override
-  bool get subscribed {
-    if (_unsubscribed) {
-      return false;
-    }
-    return super.subscribed;
-  }
-
   set subscribed(bool val) {
-    if (_unsubscribed == !val) return;
-    _unsubscribed = !val;
-    _sendUpdateTrackSettings();
+    logger.fine('setting subscribed = ${val}');
+    if (val == super.subscribed) return;
+    _sendUpdateSubscription(subscribed: val);
+    if (!val && track != null) {
+      // Ideally, we should wait for WebRTC's onRemoveTrack event
+      // but it does not work reliably across platforms.
+      // So for now we will assume remove track succeeded.
+      [_participant.events, _participant.roomEvents]
+          .emit(TrackUnsubscribedEvent(
+        participant: _participant,
+        track: track!,
+        publication: this,
+      ));
+      // Simply set to null for now
+      track = null;
+    }
   }
 
   /// for internal use
@@ -77,6 +82,15 @@ class RemoteTrackPublication extends TrackPublication {
     this.track = track;
   }
 
+  void _sendUpdateSubscription({required bool subscribed}) {
+    logger.fine('Sending update subscription... ${sid} ${subscribed}');
+    final subscription = lk_rtc.UpdateSubscription(
+      trackSids: [sid],
+      subscribe: subscribed,
+    );
+    _participant.client.sendUpdateSubscription(subscription);
+  }
+
   void _sendUpdateTrackSettings() {
     final settings = lk_rtc.UpdateTrackSettings(
       trackSids: [sid],