core: Fix handling of shuffle (fixes #453)

- Shuffle internal list when random is enabled
- Use presence of tl_track to determine if this is first run to trigger
  subsequent shuffles.

mopidy/core/tracklist.py

@@ -21,7 +21,6 @@ class TracklistController(object):
         self._version = 0
 
         self._shuffled = []
-        self._first_shuffle = True
 
     ### Properties
 
@@ -89,6 +88,9 @@ class TracklistController(object):
     def set_random(self, value):
         if self.get_random() != value:
             self._trigger_options_changed()
+        if value:
+            self._shuffled = self.tl_tracks
+            random.shuffle(self._shuffled)
         return setattr(self, '_random', value)
 
     random = property(get_random, set_random)
@@ -162,14 +164,16 @@ class TracklistController(object):
             return None
 
         if self.random and not self._shuffled:
-            if self.repeat or self._first_shuffle:
+            if self.repeat or not tl_track:
                 logger.debug('Shuffling tracks')
                 self._shuffled = self.tl_tracks
                 random.shuffle(self._shuffled)
-                self._first_shuffle = False
 
-        if self.random and self._shuffled:
-            return self._shuffled[0]
+        if self.random:
+            try:
+                return self._shuffled[0]
+            except IndexError:
+                return None
 
         if tl_track is None:
             return self.tl_tracks[0]
@@ -206,14 +210,16 @@ class TracklistController(object):
             return None
 
         if self.random and not self._shuffled:
-            if self.repeat or self._first_shuffle:
+            if self.repeat or not tl_track:
                 logger.debug('Shuffling tracks')
                 self._shuffled = self.tl_tracks
                 random.shuffle(self._shuffled)
-                self._first_shuffle = False
 
-        if self.random and self._shuffled:
-            return self._shuffled[0]
+        if self.random:
+            try:
+                return self._shuffled[0]
+            except IndexError:
+                return None
 
         if tl_track is None:
             return self.tl_tracks[0]
@@ -455,8 +461,11 @@ class TracklistController(object):
         return True
 
     def _trigger_tracklist_changed(self):
-        self._first_shuffle = True
-        self._shuffled = []
+        if self.random:
+            self._shuffled = self.tl_tracks
+            random.shuffle(self._shuffled)
+        else:
+            self._shuffled = []
 
         logger.debug('Triggering event: tracklist_changed()')
         listener.CoreListener.send('tracklist_changed')

tests/backends/local/playback_test.py

@@ -1024,15 +1024,14 @@ class LocalPlaybackProviderTest(unittest.TestCase):
         # Covers underlying issue IssueGH17RegressionTest tests for.
         shuffle_mock.side_effect = lambda tracks: tracks.reverse()
 
-        expected = self.tl_tracks[1::-1]
+        expected = self.tl_tracks[::-1] + [None]
         actual = []
 
         self.playback.play()
         self.tracklist.random = True
-        for _ in self.tracks[1:]:
+        while self.playback.state != PlaybackState.STOPPED:
             self.playback.next()
             actual.append(self.playback.current_tl_track)
-
         self.assertEqual(actual, expected)
 
     @populate_tracklist