Abstract method to determine if track number has changed.

This is a little more accurate than the previous method (check if track
is in index or medium_index) by looking at the `per_disc_numbering`
setting and comparing the index or medium index accordingly.

It's also a little more accurate in the display output by diffing the
combined `disc-track` to `medium-medium_index` (if using per disc
numbering) and intelligently colorizing the either the whole track
number or just the suffix.

beets/autotag/match.py

@@ -196,6 +196,14 @@ def assign_items(items, tracks):
     extra_tracks = set(tracks) - set(mapping.values())
     return mapping, extra_items, extra_tracks
 
+def track_index_changed(item, track_info):
+    if config['per_disc_numbering'].get(bool):
+        if item.track != track_info.medium_index:
+            return True
+    elif item.track != track_info.index:
+        return True
+    return False
+
 def track_distance(item, track_info, incl_artist=False):
     """Determines the significance of a track metadata change. Returns a
     float in [0.0,1.0]. `incl_artist` indicates that a distance
@@ -230,7 +238,7 @@ def track_distance(item, track_info, incl_artist=False):
 
     # Track index.
     if track_info.index and item.track:
-        if item.track not in (track_info.index, track_info.medium_index):
+        if track_index_changed(item, track_info):
             dist += TRACK_INDEX_WEIGHT
         dist_max += TRACK_INDEX_WEIGHT
 
@@ -374,8 +382,8 @@ def _recommendation(results):
                 rec = max_rec['tracklength']
 
             # Track number differs.
-            elif rec > max_rec['tracknumber'] and item.track not in \
-                    (track_info.index, track_info.medium_index):
+            elif rec > max_rec['tracknumber'] and \
+                    track_index_changed(item, track_info):
                 rec = max_rec['tracknumber']
 
     return rec

beets/ui/commands.py

@@ -163,14 +163,22 @@ def show_change(cur_artist, cur_album, match):
         """Return a string representing the track index of the given
         TrackInfo object.
         """
-        if config['per_disc_numbering'].get(bool):
-            if match.info.mediums > 1:
-                return u'{0}-{1}'.format(track_info.medium,
-                                         track_info.medium_index)
-            else:
-                return unicode(track_info.medium_index)
+        if isinstance(track_info, autotag.hooks.TrackInfo):
+            index = track_info.index
+            medium_index = track_info.medium_index
+            medium = track_info.medium
+            mediums = match.info.mediums
         else:
-            return unicode(track_info.index)
+            index = medium_index = track_info.track
+            medium = track_info.disc
+            mediums = track_info.disctotal
+        if config['per_disc_numbering'].get(bool):
+            if mediums > 1:
+                return u'{0}-{1}'.format(medium, medium_index)
+            else:
+                return unicode(medium_index)
+        else:
+            return unicode(index)
 
     # Identify the album in question.
     if cur_artist != match.info.artist or \
@@ -222,9 +230,14 @@ def show_change(cur_artist, cur_album, match):
         lhs_width = len(cur_title)
 
         # Track number change.
-        if item.track not in (track_info.index, track_info.medium_index):
-            cur_track, new_track = unicode(item.track), format_index(track_info)
-            lhs_track, rhs_track = ui.color_diff_suffix(cur_track, new_track)
+        cur_track, new_track = format_index(item), format_index(track_info)
+        if cur_track != new_track:
+            if (cur_track + new_track).count('-') == 1:
+                lhs_track, rhs_track = ui.colorize('red', cur_track), \
+                                       ui.colorize('red', new_track)
+            else:
+                lhs_track, rhs_track = ui.color_diff_suffix(cur_track,
+                                                            new_track)
             templ = ui.colorize('red', u' (#') + u'{0}' + \
                     ui.colorize('red', u')')
             lhs += templ.format(lhs_track)