local: Add new library interface to local backend.

This forms the basis of our plugable local libraries that we intend to ship.

mopidy/backends/local/__init__.py

@@ -37,3 +37,78 @@ class Extension(ext.Extension):
     def get_command(self):
         from .commands import LocalCommand
         return LocalCommand()
+
+
+class Library(object):
+    #: Name of the local library implementation.
+    name = None
+
+    def __init__(self, config):
+        self._config = config
+
+    def load(self):
+        """
+        Initialize whatever resources are needed for this library.
+
+        This is where you load the tracks into memory, setup a database
+        conection etc.
+
+        :rtype: :class:`int` representing number of tracks in library.
+        """
+        return 0
+
+    def add(self, track):
+        """
+        Add the given track to library.
+
+        :param track: Track to add to the library/
+        :type track: :class:`mopidy.models.Track`
+        """
+        raise NotImplementedError
+
+    def remove(self, uri):
+        """
+        Remove the given track from the library.
+
+        :param uri: URI to remove from the library/
+        :type uri: string
+        """
+        raise NotImplementedError
+
+    def commit(self):
+        """
+        Persist any changes to the library.
+
+        This is where you write your data file to disk, commit transactions
+        etc. depending on the requirements of your library implementation.
+        """
+        pass
+
+    def lookup(self, uri):
+        """
+        Lookup the given URI.
+
+        If the URI expands to multiple tracks, the returned list will contain
+        them all.
+
+        :param uri: track URI
+        :type uri: string
+        :rtype: list of :class:`mopidy.models.Track`
+        """
+        raise NotImplementedError
+
+    # TODO: support case with returning all tracks?
+    # TODO: remove uris?
+    def search(self, query=None, exact=False, uris=None):
+        """
+        Search the library for tracks where ``field`` contains ``values``.
+
+        :param query: one or more queries to search for
+        :type query: dict
+        :param exact: look for exact matches?
+        :type query: boolean
+        :param uris: zero or more URI roots to limit the search to
+        :type uris: list of strings or :class:`None`
+        :rtype: :class:`mopidy.models.SearchResult`
+        """
+        raise NotImplementedError