Don't register a natural song change twice

mpd responds twice to an 'idle' command upon a 'natural' song change
(i.e. not a skip). Checking the reason for mpd response avoids
registering twice the song change.

Fix issue #773

beetsplug/mpdstats.py

@@ -212,6 +212,8 @@ class MPDStats(object):
         To this end the difference between the song's supposed end time
         and the current time is calculated. If it's greater than a threshold,
         the song is considered skipped.
+
+        Returns whether the change was manual (skipped previous song or not)
         """
         diff = abs(song['remaining'] - (time.time() - song['started']))
 
@@ -225,6 +227,8 @@ class MPDStats(object):
         if self.do_rating:
             self.update_rating(song['beets_item'], skipped)
 
+        return skipped
+
     def handle_played(self, song):
         """Updates the play count of a song.
         """
@@ -264,19 +268,24 @@ class MPDStats(object):
         remaining = duration - played
 
         if self.now_playing and self.now_playing['path'] != path:
-            self.handle_song_change(self.now_playing)
+            skipped = self.handle_song_change(self.now_playing)
+            # mpd responds twice on a natural new song start
+            going_to_happen_twice = not skipped
+        else:
+            going_to_happen_twice = False
 
-        log.info(u'mpdstats: playing {0}', displayable_path(path))
+        if not going_to_happen_twice:
+            log.info(u'mpdstats: playing {0}', displayable_path(path))
 
-        self.now_playing = {
-            'started':    time.time(),
-            'remaining':  remaining,
-            'path':       path,
-            'beets_item': self.get_item(path),
-        }
+            self.now_playing = {
+                'started':    time.time(),
+                'remaining':  remaining,
+                'path':       path,
+                'beets_item': self.get_item(path),
+            }
 
-        self.update_item(self.now_playing['beets_item'],
-                         'last_played', value=int(time.time()))
+            self.update_item(self.now_playing['beets_item'],
+                             'last_played', value=int(time.time()))
 
     def run(self):
         self.mpd.connect()