Retrieve playlist metadata (#168)

Author: devgianlu

api/README.md

@@ -19,7 +19,7 @@ All the endpoints will respond with `200` if successful or `204` if there isn't
 - `POST \player\current` Retrieve information about the current track (metadata and time).
 
 ### Metadata
-- `POST \metadata\{type}\{uri}` Retrieve metadata. `type` can be one of `episode`, `track`, `album`, `show`, `artist`, `uri` is the standard Spotify uri.
+- `POST \metadata\{type}\{uri}` Retrieve metadata. `type` can be one of `episode`, `track`, `album`, `show`, `artist` or `playlist`, `uri` is the standard Spotify uri.
 
 ### Search
 - `POST \search\{query}` Make a search.

api/src/main/java/xyz/gianlu/librespot/api/handlers/MetadataHandler.java

@@ -11,6 +11,7 @@
 import xyz.gianlu.librespot.core.Session;
 import xyz.gianlu.librespot.dealer.ApiClient;
 import xyz.gianlu.librespot.mercury.MercuryClient;
+import xyz.gianlu.librespot.mercury.MercuryRequests;
 import xyz.gianlu.librespot.mercury.model.*;
 
 import java.io.IOException;
@@ -87,14 +88,29 @@ private JsonObject handle(@NotNull Session session, @NotNull MetadataType type,
                 return ProtobufToJson.convert(session.api().getMetadata4Episode(EpisodeId.fromUri(uri)));
             case TRACK:
                 return ProtobufToJson.convert(session.api().getMetadata4Track(TrackId.fromUri(uri)));
+            case PLAYLIST:
+                return handlePlaylist(session, uri);
             default:
                 throw new IllegalArgumentException(type.name());
         }
     }
 
+    @NotNull
+    private JsonObject handlePlaylist(@NotNull Session session, @NotNull String uri) throws IOException, MercuryClient.MercuryException {
+        JsonObject obj = new JsonObject();
+        obj.add("tracks", session.mercury().sendSync(MercuryRequests.getPlaylist(PlaylistId.fromUri(uri))).json());
+
+        try {
+            obj.add("annotations", session.mercury().sendSync(MercuryRequests.getPlaylistAnnotation(PlaylistId.fromUri(uri))).json());
+        } catch (MercuryClient.MercuryException ignored) {
+        }
+
+        return obj;
+    }
+
     private enum MetadataType {
         EPISODE("episode"), TRACK("track"), ALBUM("album"),
-        ARTIST("artist"), SHOW("show");
+        ARTIST("artist"), SHOW("show"), PLAYLIST("playlist");
 
         private final String val;