Make core.stored_playlists.save() support multibackend (#217)

mopidy/core/stored_playlists.py

@@ -31,6 +31,9 @@ class StoredPlaylistsController(object):
         :class:`None` or doesn't match a current backend, the first backend is
         asked to create the playlist.
 
+        All new playlists should be created by calling this method, and **not**
+        by creating new instances of :class:`mopidy.models.Playlist`.
+
         :param name: name of the new playlist
         :type name: string
         :param uri_scheme: use the backend matching the URI scheme
@@ -128,15 +131,28 @@ class StoredPlaylistsController(object):
         """
         Save the playlist to the set of stored playlists.
 
-        Returns the saved playlist. The return playlist may differ from the
-        saved playlist. E.g. if the playlist name was changed, the returned
-        playlist may have a different URI. The caller of this method should
-        throw away the playlist sent to this method, and use the returned
-        playlist instead.
+        For a playlist to be saveable, it must have the ``uri`` attribute set.
+        You should not set the ``uri`` atribute yourself, but use playlist
+        objects returned by :meth:`create` or retrieved from :attr:`playlists`,
+        which will always give you saveable playlists.
+
+        The method returns the saved playlist. The return playlist may differ
+        from the saved playlist. E.g. if the playlist name was changed, the
+        returned playlist may have a different URI. The caller of this method
+        should throw away the playlist sent to this method, and use the
+        returned playlist instead.
+
+        If the playlist's URI isn't set or doesn't match the URI scheme of a
+        current backend, nothing is done and :class:`None` is returned.
 
         :param playlist: the playlist
         :type playlist: :class:`mopidy.models.Playlist`
-        :rtype: :class:`mopidy.models.Playlist`
+        :rtype: :class:`mopidy.models.Playlist` or :class:`None`
         """
-        # TODO Support multiple backends
-        return self.backends[0].stored_playlists.save(playlist).get()
+        if playlist.uri is None:
+            return
+        uri_scheme = urlparse.urlparse(playlist.uri).scheme
+        if uri_scheme not in self.backends.by_uri_scheme:
+            return
+        backend = self.backends.by_uri_scheme[uri_scheme]
+        return backend.stored_playlists.save(playlist).get()

tests/core/stored_playlists_test.py

@@ -107,5 +107,38 @@ class StoredPlaylistsTest(unittest.TestCase):
         self.assertFalse(self.sp1.refresh.called)
         self.assertFalse(self.sp2.refresh.called)
 
-    # TODO The rest of the stored playlists API is pending redesign before
-    # we'll update it to support multiple backends.
+    def test_save_selects_the_dummy1_backend(self):
+        playlist = Playlist(uri='dummy1:a')
+        self.sp1.save().get.return_value = playlist
+        self.sp1.reset_mock()
+
+        result = self.core.stored_playlists.save(playlist)
+
+        self.assertEqual(playlist, result)
+        self.sp1.save.assert_called_once_with(playlist)
+        self.assertFalse(self.sp2.save.called)
+
+    def test_save_selects_the_dummy2_backend(self):
+        playlist = Playlist(uri='dummy2:a')
+        self.sp2.save().get.return_value = playlist
+        self.sp2.reset_mock()
+
+        result = self.core.stored_playlists.save(playlist)
+
+        self.assertEqual(playlist, result)
+        self.assertFalse(self.sp1.save.called)
+        self.sp2.save.assert_called_once_with(playlist)
+
+    def test_save_does_nothing_if_playlist_uri_is_unset(self):
+        result = self.core.stored_playlists.save(Playlist())
+
+        self.assertIsNone(result)
+        self.assertFalse(self.sp1.save.called)
+        self.assertFalse(self.sp2.save.called)
+
+    def test_save_does_nothing_if_playlist_uri_has_unknown_scheme(self):
+        result = self.core.stored_playlists.save(Playlist(uri='foobar:a'))
+
+        self.assertIsNone(result)
+        self.assertFalse(self.sp1.save.called)
+        self.assertFalse(self.sp2.save.called)