Add support for negative songpos arg in 'playlistinfo' as used by ncmpc

mopidy/models.py

@@ -196,15 +196,24 @@ class Playlist(ImmutableObject):
         Optionally limit output to the slice ``[start:end]`` of the playlist.
 
         :param start: position of first track to include in output
-        :type start: int
+        :type start: int (positive or negative)
         :param end: position after last track to include in output
-        :type end: int or :class:`None` for end of list
+        :type end: int (positive or negative) or :class:`None` for end of list
         :rtype: list of lists of two-tuples
         """
-        if end is None:
-            end = self.length
+        if start < 0:
+            range_start = self.length + start
+        else:
+            range_start = start
+        if end is not None and end < 0:
+            range_end = self.length - end
+        elif end is not None and end >= 0:
+            range_end = end
+        else:
+            range_end = self.length
         tracks = []
-        for track, position in zip(self.tracks[start:end], range(start, end)):
+        for track, position in zip(self.tracks[start:end],
+                range(range_start, range_end)):
             tracks.append(track.mpd_format(position, search_result))
         return tracks
 

mopidy/mpd/handler.py

@@ -394,7 +394,7 @@ class MpdHandler(object):
             return self.backend.current_playlist.playlist.mpd_format()
 
     @handle_pattern(r'^playlistinfo$')
-    @handle_pattern(r'^playlistinfo "(?P<songpos>\d+)"$')
+    @handle_pattern(r'^playlistinfo "(?P<songpos>-?\d+)"$')
     @handle_pattern(r'^playlistinfo "(?P<start>\d+):(?P<end>\d+)*"$')
     def _current_playlist_playlistinfo(self, songpos=None,
             start=None, end=None):
@@ -406,11 +406,20 @@ class MpdHandler(object):
             Displays a list of all songs in the playlist, or if the optional
             argument is given, displays information only for the song
             ``SONGPOS`` or the range of songs ``START:END``.
+
+        *ncmpc:*
+
+        - uses negative indexes, like ``playlistinfo "-1"``, to request
+          information on the last track in the playlist.
         """
         if songpos is not None:
             songpos = int(songpos)
+            start = songpos
+            end = songpos + 1
+            if start == -1:
+                end = None
             return self.backend.current_playlist.playlist.mpd_format(
-                songpos, songpos + 1)
+                start, end)
         else:
             if start is None:
                 start = 0

tests/modelstest.py

@@ -182,6 +182,20 @@ class PlaylistTest(unittest.TestCase):
         self.assertEqual(len(result), 1)
         self.assertEqual(dict(result[0])['Track'], 2)
 
+    def test_mpd_format_with_negative_start_and_no_end(self):
+        playlist = Playlist(tracks=[
+            Track(track_no=1), Track(track_no=2), Track(track_no=3)])
+        result = playlist.mpd_format(-1, None)
+        self.assertEqual(len(result), 1)
+        self.assertEqual(dict(result[0])['Track'], 3)
+
+    def test_mpd_format_with_negative_start_and_end(self):
+        playlist = Playlist(tracks=[
+            Track(track_no=1), Track(track_no=2), Track(track_no=3)])
+        result = playlist.mpd_format(-2, -1)
+        self.assertEqual(len(result), 1)
+        self.assertEqual(dict(result[0])['Track'], 2)
+
     def test_with_new_uri(self):
         tracks = [Track()]
         last_modified = dt.datetime.now()

tests/mpd/handlertest.py

@@ -701,6 +701,10 @@ class CurrentPlaylistHandlerTest(unittest.TestCase):
         result = self.h.handle_request(u'playlistinfo "5"')
         self.assert_(u'OK' in result)
 
+    def test_playlistinfo_with_negative_songpos(self):
+        result = self.h.handle_request(u'playlistinfo "-1"')
+        self.assert_(u'OK' in result)
+
     def test_playlistinfo_with_open_range(self):
         result = self.h.handle_request(u'playlistinfo "10:"')
         self.assert_(u'OK' in result)