local: Add library update provider for tag caches.

This adds the basic interface implemenations for supporting tag caches using
the new update APIs.

mopidy/backends/local/actor.py

@@ -8,7 +8,7 @@ import pykka
 from mopidy.backends import base
 from mopidy.utils import encoding, path
 
-from .library import LocalLibraryProvider
+from .library import LocalLibraryProvider, LocalLibraryUpdateProvider
 from .playlists import LocalPlaylistsProvider
 
 logger = logging.getLogger('mopidy.backends.local')
@@ -23,6 +23,7 @@ class LocalBackend(pykka.ThreadingActor, base.Backend):
         self.check_dirs_and_files()
 
         self.library = LocalLibraryProvider(backend=self)
+        self.updater = LocalLibraryUpdateProvider(backend=self)
         self.playback = base.BasePlaybackProvider(audio=audio, backend=self)
         self.playlists = LocalPlaylistsProvider(backend=self)
 

mopidy/backends/local/library.py

@@ -1,7 +1,11 @@
 from __future__ import unicode_literals
 
 import logging
+import os
+import tempfile
+
 from mopidy.backends import base
+from mopidy.frontends.mpd import translator as mpd_translator
 from mopidy.models import Album, SearchResult
 
 from .translator import parse_mpd_tag_cache
@@ -127,3 +131,43 @@ class LocalLibraryProvider(base.BaseLibraryProvider):
             for value in values:
                 if not value:
                     raise LookupError('Missing query')
+
+
+# TODO: rename and move to tagcache extension.
+class LocalLibraryUpdateProvider(base.BaseLibraryProvider):
+    def __init__(self, *args, **kwargs):
+        super(LocalLibraryUpdateProvider, self).__init__(*args, **kwargs)
+        self._tracks = {}
+        self._media_dir = self.backend.config['local']['media_dir']
+        self._tag_cache_file = self.backend.config['local']['tag_cache_file']
+
+    def load(self):
+        tracks = parse_mpd_tag_cache(self._tag_cache_file, self._media_dir)
+        for track in tracks:
+            self._tracks[track.uri] = track
+        return tracks
+
+    def add(self, track):
+        self._tracks[track.uri] = track
+
+    def remove(self, uri):
+        if uri in self._tracks:
+            del self._tracks[uri]
+
+    def commit(self):
+        directory, basename = os.path.split(self._tag_cache_file)
+        tmp = tempfile.NamedTemporaryFile(
+            prefix=basename + '.', dir=directory, delete=False)
+
+        try:
+            for row in mpd_translator.tracks_to_tag_cache_format(
+                    self._tracks.values(), self._media_dir):
+                if len(row) == 1:
+                    tmp.write(('%s\n' % row).encode('utf-8'))
+                else:
+                    tmp.write(('%s: %s\n' % row).encode('utf-8'))
+
+            os.rename(tmp.name, self._tag_cache_file)
+        finally:
+            if os.path.exists(tmp.name):
+                os.remove(tmp.name)

mopidy/frontends/mpd/translator.py

@@ -10,6 +10,8 @@ from mopidy.frontends.mpd.exceptions import MpdArgError
 from mopidy.models import TlTrack
 from mopidy.utils.path import mtime as get_mtime, uri_to_path, split_path
 
+# TODO: special handling of local:// uri scheme
+
 
 def track_to_mpd_format(track, position=None):
     """
@@ -213,6 +215,7 @@ def query_from_mpd_search_format(mpd_query):
     return query
 
 
+# TODO: move to tagcache backend.
 def tracks_to_tag_cache_format(tracks, media_dir):
     """
     Format list of tracks for output to MPD tag cache
@@ -234,6 +237,7 @@ def tracks_to_tag_cache_format(tracks, media_dir):
     _add_to_tag_cache(result, dirs, files, media_dir)
     return result
 
+
 # TODO: bytes only
 def _add_to_tag_cache(result, dirs, files, media_dir):
     base_path = media_dir.encode('utf-8')