playlist: Give playlists functions for moving individual tracks

The move_track_up() and move_track_down() functions are used to manually
arrange the tracks in a playlist.

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

emmental/playlist/playlist.py

@@ -29,6 +29,18 @@ class Playlist(model.TrackidModel):
                 self.on_trackids_reset(plist.tracks)
                 self.notify("sort-order")
 
+    def __track_moved(self, track: db.tracks.Track, *, offset: int) -> None:
+        index = self.index(track)
+        new_pos = index + offset
+        n_changed = abs(offset) + 1
+
+        del self.trackids[index]
+        self.trackids.insert(new_pos, track.trackid)
+
+        self.__sort_keys = self.__playlist.get_track_order()
+        self.items_changed(position=min(index, new_pos),
+                           removed=n_changed, added=n_changed)
+
     def do_get_sort_key(self, trackid: int) -> int:
         """Get a sort key for the given trackid."""
         if (key := self.__sort_keys.get(trackid)) is None:
@@ -60,6 +72,20 @@ class Playlist(model.TrackidModel):
         if track is not None:
             return super().index(track.trackid)
 
+    def move_track_down(self, track: db.tracks.Track) -> None:
+        """Move a track earlier in the sort order."""
+        if self.__playlist is not None:
+            need_handling = self.__sort_order == "user"
+            if self.__playlist.move_track_down(track) and need_handling:
+                self.__track_moved(track, offset=1)
+
+    def move_track_up(self, track: db.tracks.Track) -> None:
+        """Move a track earlier in the sort order."""
+        if self.__playlist is not None:
+            need_handling = self.__sort_order == "user"
+            if self.__playlist.move_track_up(track) and need_handling:
+                self.__track_moved(track, offset=-1)
+
     def remove_track(self, track: db.tracks.Track) -> None:
         """Remove a track from the playlist."""
         if self.__playlist is not None:

tests/playlist/test_playlist.py

@@ -73,6 +73,74 @@ class TestPlaylist(tests.util.TestCase):
         self.assertIsNone(super(type(self.playlist), self.playlist).index(0))
         self.assertIsNone(self.playlist.index(None))
 
+    def test_move_track_down(self):
+        """Test the playlist move_track_down() function."""
+        self.playlist.move_track_down(self.track1)
+
+        self.db_plist.add_track(self.track1)
+        self.db_plist.add_track(self.track2)
+        self.db_plist.add_track(self.track3)
+        self.playlist.playlist = self.db_plist
+
+        items_changed = unittest.mock.Mock()
+        self.playlist.connect("items-changed", items_changed)
+
+        self.playlist.move_track_down(self.track2)
+        self.assertEqual(self.db_plist.sort_order, "user")
+        self.assertDictEqual(self.playlist._Playlist__sort_keys,
+                             {self.track1.trackid: 0,
+                              self.track3.trackid: 1,
+                              self.track2.trackid: 2})
+        self.assertListEqual(self.playlist.trackids, [self.track1.trackid,
+                                                      self.track3.trackid,
+                                                      self.track2.trackid])
+        items_changed.assert_called_once_with(self.playlist, 0, 3, 3)
+
+        items_changed.reset_mock()
+        self.playlist.move_track_down(self.track1)
+        self.assertDictEqual(self.playlist._Playlist__sort_keys,
+                             {self.track3.trackid: 0,
+                              self.track1.trackid: 1,
+                              self.track2.trackid: 2})
+        self.assertListEqual(self.playlist.trackids, [self.track3.trackid,
+                                                      self.track1.trackid,
+                                                      self.track2.trackid])
+        items_changed.assert_called_once_with(self.playlist, 0, 2, 2)
+
+    def test_move_track_up(self):
+        """Test the playlist move_track_up() function."""
+        self.playlist.move_track_up(self.track1)
+
+        self.db_plist.add_track(self.track1)
+        self.db_plist.add_track(self.track2)
+        self.db_plist.add_track(self.track3)
+        self.playlist.playlist = self.db_plist
+
+        items_changed = unittest.mock.Mock()
+        self.playlist.connect("items-changed", items_changed)
+
+        self.playlist.move_track_up(self.track2)
+        self.assertEqual(self.db_plist.sort_order, "user")
+        self.assertDictEqual(self.playlist._Playlist__sort_keys,
+                             {self.track2.trackid: 0,
+                              self.track1.trackid: 1,
+                              self.track3.trackid: 2})
+        self.assertListEqual(self.playlist.trackids, [self.track2.trackid,
+                                                      self.track1.trackid,
+                                                      self.track3.trackid])
+        items_changed.assert_called_once_with(self.playlist, 0, 3, 3)
+
+        items_changed.reset_mock()
+        self.playlist.move_track_up(self.track3)
+        self.assertDictEqual(self.playlist._Playlist__sort_keys,
+                             {self.track2.trackid: 0,
+                              self.track3.trackid: 1,
+                              self.track1.trackid: 2})
+        self.assertListEqual(self.playlist.trackids, [self.track2.trackid,
+                                                      self.track3.trackid,
+                                                      self.track1.trackid])
+        items_changed.assert_called_once_with(self.playlist, 1, 2, 2)
+
     def test_remove_track(self):
         """Test the playlist remove_track() function."""
         self.playlist.remove_track(self.track1)