added MusicBrainz query layer (needs docs and tests)

--HG--
extra : convert_revision : svn%3A41726ec3-264d-0410-9c23-a9f1637257cc/trunk%40192

beets/autotag/mb.py

@@ -0,0 +1,75 @@
+import re
+import time
+import datetime
+import musicbrainz2.webservice as mbws
+
+QUERY_WAIT_TIME = 1.0
+last_query_time = 0.0
+def query_wait():
+    global last_query_time
+
+    now = time.time()
+    while now - last_query_time < QUERY_WAIT_TIME:
+        time.sleep(QUERY_WAIT_TIME - (now - last_query_time))
+        now = time.time()
+
+    last_query_time = now
+
+# Regex stolen from MusicBrainz Picard.
+def lucene_escape(text):
+    return re.sub(r'([+\-&|!(){}\[\]\^"~*?:\\])', r'\\\1', text)
+
+# Workings more or less stolen from Picard.
+def find_releases(criteria, limit=25):
+    # Build Lucene query (the MusicBrainz 'query' filter).
+    query_parts = []
+    for name, value in criteria.items():
+        value = lucene_escape(value).strip().lower()
+        if value:
+            query_parts.append('%s:(%s)' % (name, value.encode('utf-8')))
+    query = ' '.join(query_parts)
+    
+    # Build the filter and send the query.
+    filter = mbws.ReleaseFilter(limit=limit, query=query)
+    query_wait()
+    query = mbws.Query()
+    return query.getReleases(filter=filter)
+
+def release_dict(release):
+    out = {'album':     release.title,
+           'album_id':  release.id,
+           'artist':    release.artist.name,
+           'artist_id': release.artist.id,
+          }
+
+    date_str = release.getEarliestReleaseDate()
+    try:
+        # If the date-string is just an integer, then it's the release
+        # year.
+        out['year'] = int(date_str)
+    except ValueError:
+        # Otherwise, it is a full date in the format YYYY-MM-DD.
+        timestamp = time.mktime(time.strptime(date_str, '%Y-%m-%d'))
+        date = datetime.date.fromtimestamp(timestamp)
+        out.update({'year':  date.year,
+                    'month': date.month,
+                    'day':   date.day,
+                   })
+
+    return out
+
+def match_album(artist, album, tracks=None):
+    criteria = {'artist':  artist, 'release': album}
+    if tracks is not None:
+        criteria['tracks'] = str(tracks)
+
+    results = find_releases(criteria, 1)
+    if not results:
+        return None
+    return release_dict(results[0].release)
+
+
+if __name__ == '__main__':
+    print match_album('the little ones', 'morning tide')
+    print match_album('the 6ths', 'hyacinths and thistles')
+