core: Make index return current index when missing args

mopidy/core/tracklist.py

@@ -204,6 +204,9 @@ class TracklistController(object):
         """
         The position of the given track in the tracklist.
 
+        If neither *tl_track* or *tlid* is given we return the index of
+        the currently playing track.
+
         :param tl_track: the track to find the index of
         :type tl_track: :class:`mopidy.models.TlTrack` or :class:`None`
         :param tlid: of the track to find the index of
@@ -216,6 +219,9 @@ class TracklistController(object):
         tl_track is None or validation.check_instance(tl_track, TlTrack)
         tlid is None or validation.check_integer(tlid, min=0)
 
+        if tl_track is None and tlid is None:
+            tl_track = self.core.playback.get_current_tl_track()
+
         if tl_track is not None:
             try:
                 return self._tl_tracks.index(tl_track)

tests/core/test_tracklist.py

@@ -117,9 +117,11 @@ class TracklistIndexTest(unittest.TestCase):
             return {u: [t for t in self.tracks if t.uri == u] for u in uris}
 
         self.core = core.Core(mixer=None, backends=[])
-        self.core.library.lookup = mock.Mock()
+        self.core.library = mock.Mock(spec=core.LibraryController)
         self.core.library.lookup.side_effect = lookup
 
+        self.core.playback = mock.Mock(spec=core.PlaybackController)
+
         self.tl_tracks = self.core.tracklist.add(uris=[
             t.uri for t in self.tracks])
 
@@ -154,3 +156,12 @@ class TracklistIndexTest(unittest.TestCase):
     def test_index_errors_out_for_invalid_tlid(self):
         with self.assertRaises(ValueError):
             self.core.tracklist.index(tlid=-1)
+
+    def test_index_without_args_returns_current_tl_track_index(self):
+        self.core.playback.get_current_tl_track.side_effect = [
+            None, self.tl_tracks[0], self.tl_tracks[1], self.tl_tracks[2]]
+
+        self.assertEqual(None, self.core.tracklist.index())
+        self.assertEqual(0, self.core.tracklist.index())
+        self.assertEqual(1, self.core.tracklist.index())
+        self.assertEqual(2, self.core.tracklist.index())