backend: Add playlists.as_list() and playlists.get_items(uri)

mopidy/backend.py

@@ -318,6 +318,36 @@ class PlaylistsProvider(object):
     def playlists(self, playlists):
         raise NotImplementedError
 
+    def as_list(self):
+        """
+        Get a list of the currently available playlists.
+
+        Returns a list of :class:`~mopidy.models.Ref` objects referring to the
+        playlists. In other words, no information about the playlists' content
+        is given.
+
+        :rtype: list of :class:`mopidy.models.Ref`
+
+        .. versionadded:: 1.0
+        """
+        raise NotImplementedError
+
+    def get_items(self, uri):
+        """
+        Get the items in a playlist specified by ``uri``.
+
+        Returns a list of :class:`~mopidy.models.Ref` objects referring to the
+        playlist's items.
+
+        If a playlist with the given ``uri`` doesn't exist, it returns
+        :class:`None`.
+
+        :rtype: list of :class:`mopidy.models.Ref`, or :class:`None`
+
+        .. versionadded:: 1.0
+        """
+        raise NotImplementedError
+
     def create(self, name):
         """
         Create a new empty playlist with the given name.

tests/backend/test_backend.py

@@ -8,6 +8,7 @@ from tests import dummy_backend
 
 
 class LibraryTest(unittest.TestCase):
+
     def test_default_get_images_impl_falls_back_to_album_image(self):
         album = models.Album(images=['imageuri'])
         track = models.Track(uri='trackuri', album=album)
@@ -31,10 +32,20 @@ class LibraryTest(unittest.TestCase):
 
 
 class PlaylistsTest(unittest.TestCase):
-    def test_playlists_default_impl(self):
-        playlists = backend.PlaylistsProvider(backend=None)
 
-        self.assertEqual(playlists.playlists, [])
+    def setUp(self):  # noqa: N802
+        self.provider = backend.PlaylistsProvider(backend=None)
+
+    def test_playlists_default_impl(self):
+        self.assertEqual(self.provider.playlists, [])
 
         with self.assertRaises(NotImplementedError):
-            playlists.playlists = []
+            self.provider.playlists = []
+
+    def test_as_list_default_impl(self):
+        with self.assertRaises(NotImplementedError):
+            self.provider.as_list()
+
+    def test_get_items_default_impl(self):
+        with self.assertRaises(NotImplementedError):
+            self.provider.get_items('some uri')

tests/dummy_backend.py

@@ -100,6 +100,17 @@ class DummyPlaylistsProvider(backend.PlaylistsProvider):
         super(DummyPlaylistsProvider, self).__init__(backend)
         self._playlists = []
 
+    def as_list(self):
+        return [
+            Ref.playlist(uri=pl.uri, name=pl.name) for pl in self._playlists]
+
+    def get_items(self, uri):
+        playlist = self._playlists.get(uri)
+        if playlist is None:
+            return
+        return [
+            Ref.track(uri=t.uri, name=t.name) for t in playlist.tracks]
+
     @property
     def playlists(self):
         return copy.copy(self._playlists)