core: Add uris argument to library.lookup (Fixes #1008)

For now this doesn't add any corresponding APIs to backends, or for that matter
tracklist.add(uris). This is just to get the API in for clients in 0.20.

docs/changelog.rst

@@ -31,6 +31,9 @@ v0.20.0 (UNRELEASED)
 - Add :class:`mopidy.core.MixerController` which keeps track of volume and
   mute. (Fixes: :issue:`962`)
 
+- Add ``uris`` argument to :method:`mopidy.core.LibraryController.lookup`
+  which allows for simpler lookup of multiple URIs. (Fixes: :issue:`1008`)
+
 - **Deprecated:** The old methods on :class:`mopidy.core.PlaybackController` for
   volume and mute management have been deprecated. (Fixes: :issue:`962`)
 

mopidy/core/library.py

@@ -162,22 +162,41 @@ def find_exact(self, query=None, uris=None, **kwargs):
             in self._get_backends_to_uris(uris).items()]
         return [result for result in pykka.get_all(futures) if result]
 
-    def lookup(self, uri):
+    def lookup(self, uri=None, uris=None):
         """
         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`
+        :type uri: string or :class:`None`
+        :param uris: track URIs
+        :type uris: list of string or :class:`None`
+        :rtype: list of :class:`mopidy.models.Track` if uri was set or a
+            ``{uri: list of tracks}`` if uris was set.
         """
-        backend = self._get_backend(uri)
-        if backend:
-            return backend.library.lookup(uri).get()
-        else:
-            return []
+        none_set = uri is None and uris is None
+        both_set = uri is not None and uris is not None
+
+        if none_set or both_set:
+            raise ValueError("One of 'uri' or 'uris' must be set")
+
+        futures = {}
+        result = {}
+        backends = self._get_backends_to_uris([uri] if uri else uris)
+
+        # TODO: lookup(uris) to backend APIs
+        for backend, backend_uris in backends.items():
+            for u in backend_uris or []:
+                futures[u] = backend.library.lookup(u)
+
+        for u, future in futures.items():
+            result[u] = future.get()
+
+        if uri:
+            return result.get(uri, [])
+        return result
 
     def refresh(self, uri=None):
         """

tests/core/test_library.py

@@ -157,6 +157,17 @@ def test_lookup_selects_dummy2_backend(self):
         self.assertFalse(self.library1.lookup.called)
         self.library2.lookup.assert_called_once_with('dummy2:a')
 
+    def test_lookup_fails_with_uri_and_uris_set(self):
+        with self.assertRaises(ValueError):
+            self.core.library.lookup('dummy1:a', ['dummy2:a'])
+
+    def test_lookup_can_handle_uris(self):
+        self.library1.lookup().get.return_value = [1234]
+        self.library2.lookup().get.return_value = [5678]
+
+        result = self.core.library.lookup(uris=['dummy1:a', 'dummy2:a'])
+        self.assertEqual(result, {'dummy2:a': [5678], 'dummy1:a': [1234]})
+
     def test_lookup_returns_nothing_for_dummy3_track(self):
         result = self.core.library.lookup('dummy3:a')