Introduce new module beets.util.id_extractors

- We introduce a new submodule of beets.util named id_extractors.
- Parts of the ID extraction utilites required by metadata source plugins
  should live there.
- Also this enables future usage of those utilities from the "outside" of
  metadata source plugins.
- Move Discogs ID extractor to the new module and change test_discogs to use
  the new location.
- Add spotify_id_regex variable to the new module.

beets/util/id_extractors.py

@@ -0,0 +1,49 @@
+# This file is part of beets.
+# Copyright 2016, Adrian Sampson.
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+
+"""Helpers around the extraction of album/track ID's from metadata sources."""
+
+import re
+
+# Spotify IDs consist of 22 alphanumeric characters
+# (zero-left-padded base62 representation of randomly generated UUID4)
+spotify_id_regex = {
+    'pattern': r'(^|open\.spotify\.com/{}/)([0-9A-Za-z]{{22}})',
+    'match_group': 2,
+}
+
+
+def extract_discogs_id_regex(album_id):
+    """Returns the Discogs_id or None."""
+    # Discogs-IDs are simple integers. In order to avoid confusion with
+    # other metadata plugins, we only look for very specific formats of the
+    # input string:
+    # - plain integer, optionally wrapped in brackets and prefixed by an
+    #   'r', as this is how discogs displays the release ID on its webpage.
+    # - legacy url format: discogs.com/<name of release>/release/<id>
+    # - current url format: discogs.com/release/<id>-<name of release>
+    # See #291, #4080 and #4085 for the discussions leading up to these
+    # patterns.
+    # Regex has been tested here https://regex101.com/r/wyLdB4/2
+
+    for pattern in [
+            r'^\[?r?(?P<id>\d+)\]?$',
+            r'discogs\.com/release/(?P<id>\d+)-',
+            r'discogs\.com/[^/]+/release/(?P<id>\d+)',
+    ]:
+        match = re.search(pattern, album_id)
+        if match:
+            return int(match.group('id'))
+
+    return None

beetsplug/discogs.py

@@ -18,6 +18,7 @@ python3-discogs-client library.
 
 import beets.ui
 from beets import config
+from beets.util.id_extractors import extract_discogs_id_regex
 from beets.autotag.hooks import AlbumInfo, TrackInfo
 from beets.plugins import MetadataSourcePlugin, BeetsPlugin, get_distance
 import confuse
@@ -218,31 +219,6 @@ class DiscogsPlugin(BeetsPlugin):
         # first 10 results, don't overwhelm with options
         return candidates[:10]
 
-    @staticmethod
-    def extract_release_id_regex(album_id):
-        """Returns the Discogs_id or None."""
-        # Discogs-IDs are simple integers. In order to avoid confusion with
-        # other metadata plugins, we only look for very specific formats of the
-        # input string:
-        # - plain integer, optionally wrapped in brackets and prefixed by an
-        #   'r', as this is how discogs displays the release ID on its webpage.
-        # - legacy url format: discogs.com/<name of release>/release/<id>
-        # - current url format: discogs.com/release/<id>-<name of release>
-        # See #291, #4080 and #4085 for the discussions leading up to these
-        # patterns.
-        # Regex has been tested here https://regex101.com/r/wyLdB4/2
-
-        for pattern in [
-                r'^\[?r?(?P<id>\d+)\]?$',
-                r'discogs\.com/release/(?P<id>\d+)-',
-                r'discogs\.com/[^/]+/release/(?P<id>\d+)',
-        ]:
-            match = re.search(pattern, album_id)
-            if match:
-                return int(match.group('id'))
-
-        return None
-
     def album_for_id(self, album_id):
         """Fetches an album by its Discogs ID and returns an AlbumInfo object
         or None if the album is not found.
@@ -252,7 +228,7 @@ class DiscogsPlugin(BeetsPlugin):
 
         self._log.debug('Searching for release {0}', album_id)
 
-        discogs_id = self.extract_release_id_regex(album_id)
+        discogs_id = extract_discogs_id_regex(album_id)
 
         if not discogs_id:
             return None
@@ -365,7 +341,7 @@ class DiscogsPlugin(BeetsPlugin):
         else:
             genre = base_genre
 
-        discogs_albumid = self.extract_release_id_regex(result.data.get('uri'))
+        discogs_albumid = extract_discogs_id_regex(result.data.get('uri'))
 
         # Extract information for the optional AlbumInfo fields that are
         # contained on nested discogs fields.

test/test_discogs.py

@@ -21,6 +21,7 @@ from test._common import Bag
 from test.helper import capture_log
 
 from beets import config
+from beets.util.id_extractors import extract_discogs_id_regex
 
 from beetsplug.discogs import DiscogsPlugin
 
@@ -371,7 +372,7 @@ class DGAlbumInfoTest(_common.TestCase):
                          ('005b84a0-ecd6-39f1-b2f6-6eb48756b268', ''),
                          ]
         for test_pattern, expected in test_patterns:
-            match = DiscogsPlugin.extract_release_id_regex(test_pattern)
+            match = extract_discogs_id_regex(test_pattern)
             if not match:
                 match = ''
             self.assertEqual(match, expected)