add functional result handler

src/main/java/lavalink/client/io/FunctionalResultHandler.java

@@ -0,0 +1,71 @@
+package lavalink.client.io;
+
+import lavalink.client.player.track.AudioPlaylist;
+import lavalink.client.player.track.AudioTrack;
+
+import java.util.List;
+import java.util.function.Consumer;
+
+/**
+ * Helper class for creating an audio result handler using only methods that can be passed as lambdas.
+ */
+public class FunctionalResultHandler implements LoadResultHandler {
+    private final Consumer<AudioTrack> trackConsumer;
+    private final Consumer<AudioPlaylist> playlistConsumer;
+    private final Consumer<List<AudioTrack>> searchResultConsumer;
+    private final Runnable emptyResultHandler;
+    private final Consumer<FriendlyException> exceptionConsumer;
+
+    /**
+     * Refer to {@link LoadResultHandler} methods for details on when each method is called.
+     *
+     * @param trackConsumer Consumer for single track result
+     * @param playlistConsumer Consumer for playlist result
+     * @param searchResultConsumer Consumer for search result
+     * @param emptyResultHandler Empty result handler
+     * @param exceptionConsumer Consumer for an exception when loading the item fails
+     */
+    public FunctionalResultHandler(Consumer<AudioTrack> trackConsumer, Consumer<AudioPlaylist> playlistConsumer, Consumer<List<AudioTrack>> searchResultConsumer, Runnable emptyResultHandler, Consumer<FriendlyException> exceptionConsumer) {
+        this.trackConsumer = trackConsumer;
+        this.playlistConsumer = playlistConsumer;
+        this.searchResultConsumer = searchResultConsumer;
+        this.emptyResultHandler = emptyResultHandler;
+        this.exceptionConsumer = exceptionConsumer;
+    }
+
+    @Override
+    public void trackLoaded(AudioTrack track) {
+        if (trackConsumer != null) {
+            trackConsumer.accept(track);
+        }
+    }
+
+    @Override
+    public void playlistLoaded(AudioPlaylist playlist) {
+        if (playlistConsumer != null) {
+            playlistConsumer.accept(playlist);
+        }
+    }
+
+    @Override
+    public void searchResultLoaded(List<AudioTrack> tracks) {
+        if (searchResultConsumer != null) {
+            searchResultConsumer.accept(tracks);
+        }
+    }
+
+    @Override
+    public void noMatches() {
+        if (emptyResultHandler != null) {
+            emptyResultHandler.run();
+        }
+    }
+
+    @Override
+    public void loadFailed(FriendlyException exception) {
+        if (exceptionConsumer != null) {
+            exceptionConsumer.accept(exception);
+        }
+    }
+}
+