Return track images via library get_images(), fixing mopidy#111

Previously, track images were provided via album images. That is
obsolete in Mopidy 3, and was removed in e4efb79. This uses the
new LibraryProvider get_images() API to provide images.

The same SoundCloud API request used to lookup() a track also
provides the image URL. These requests are now cached via
_get_track_data().

Like in the previous implementation, user avatar is used if there
is no track image.

mopidy_soundcloud/library.py

@@ -4,7 +4,7 @@
 import urllib.parse
 
 from mopidy import backend, models
-from mopidy.models import SearchResult, Track
+from mopidy.models import SearchResult, Track, Image
 from mopidy_soundcloud.soundcloud import safe_url
 
 logger = logging.getLogger(__name__)
@@ -157,3 +157,15 @@ def lookup(self, uri):
         except Exception as error:
             logger.error(f"Failed to lookup {uri}: {error}")
             return []
+
+    def get_images(self, uris):
+        images = {}
+        for uri in uris:
+            if uri.startswith("soundcloud:song/"):
+                track_id = self.backend.remote.parse_track_uri(uri)
+                imguri = self.backend.remote.get_track_image(track_id)
+                if imguri is not None:
+                    image = Image(uri=imguri)
+                    images[uri] = [image]
+
+        return images

mopidy_soundcloud/soundcloud.py

@@ -232,7 +232,19 @@ def get_tracks(self, user_id=None):
     def get_track(self, track_id, streamable=False):
         logger.debug("Getting info for track with ID {track_id}")
         try:
-            return self.parse_track(self._get(f"tracks/{track_id}"), streamable)
+            return self.parse_track(self._get_track_data(track_id), streamable)
+        except Exception:
+            return None
+
+    def get_track_image(self, track_id):
+        try:
+            data = self._get_track_data(track_id)
+            image = data.get("artwork_url")
+            if image is None:
+                image = data.get("user", {}).get("avatar_url")
+            if image is not None:
+                image = image.replace("large", "t500x500")
+            return image
         except Exception:
             return None
 
@@ -291,6 +303,10 @@ def _get(self, url, limit=None):
                 logger.error(f"SoundCloud API request failed: {e}")
         return {}
 
+    @cache()
+    def _get_track_data(self, track_id):
+        return self._get(f"tracks/{track_id}")
+
     def sanitize_tracks(self, tracks):
         return [t for t in tracks if t]