Support priorities for event listeners

src/api/java/baritone/api/event/listener/IEventBus.java

@@ -21,6 +21,8 @@
  * A type of {@link IGameEventListener} that can have additional listeners
  * registered so that they receive the events that are dispatched to this
  * listener.
+ * <p>
+ * Listeners with higher priority will be called first.
  *
  * @author Brady
  * @since 11/14/2018
@@ -29,8 +31,17 @@ public interface IEventBus extends IGameEventListener {
 
     /**
      * Registers the specified {@link IGameEventListener} to this event bus
+     * using a default priority {@code 0}
      *
      * @param listener The listener
      */
     void registerEventListener(IGameEventListener listener);
+
+    /**
+     * Registers the specified {@link IGameEventListener} to this event bus.
+     *
+     * @param priority The listener priority
+     * @param listener The listener
+     */
+    void registerEventListener(int priority, IGameEventListener listener);
 }

src/main/java/baritone/event/GameEventHandler.java

@@ -27,6 +27,8 @@
 import baritone.cache.CachedChunk;
 import baritone.cache.WorldProvider;
 import baritone.utils.BlockStateInterface;
+import it.unimi.dsi.fastutil.ints.IntList;
+import it.unimi.dsi.fastutil.ints.IntArrayList;
 import net.minecraft.world.level.ChunkPos;
 import net.minecraft.world.level.Level;
 import net.minecraft.world.level.block.state.BlockState;
@@ -43,7 +45,9 @@ public final class GameEventHandler implements IEventBus, Helper {
 
     private final Baritone baritone;
 
+    // reading/iterating `listeners` is allowed without synchronization
     private final List<IGameEventListener> listeners = new CopyOnWriteArrayList<>();
+    private final IntList priorities = new IntArrayList();
 
     public GameEventHandler(Baritone baritone) {
         this.baritone = baritone;
@@ -184,6 +188,16 @@ public void onPathEvent(PathEvent event) {
 
     @Override
     public final void registerEventListener(IGameEventListener listener) {
-        this.listeners.add(listener);
+        this.registerEventListener(0, listener);
+    }
+
+    @Override
+    public final synchronized void registerEventListener(int priority, IGameEventListener listener) {
+        int i = 0;
+        while (i < this.listeners.size() && priority <= this.priorities.getInt(i)) {
+            ++i;
+        }
+        this.listeners.add(i, listener);
+        this.priorities.add(i, priority);
     }
 }

src/test/java/baritone/event/GameEventHandlerTest.java

@@ -0,0 +1,68 @@
+/*
+ * This file is part of Baritone.
+ *
+ * Baritone is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Baritone is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with Baritone.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package baritone.event;
+
+import baritone.api.event.listener.AbstractGameEventListener;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+public class GameEventHandlerTest {
+
+    @Test
+    public void testListenerOrder() {
+        GameEventHandler bus = new GameEventHandler(null /* baritone */);
+
+        List<String> output = new ArrayList<>();
+
+        bus.registerEventListener(0, new TestEventListener("0 0", output));
+        bus.registerEventListener(0, new TestEventListener("0 1", output));
+        bus.registerEventListener(1, new TestEventListener("1 2", output));
+        bus.registerEventListener(new TestEventListener("_ 3", output));
+        bus.registerEventListener(-1, new TestEventListener("-1 4", output));
+        bus.registerEventListener(1, new TestEventListener("1 5", output));
+        bus.registerEventListener(0, new TestEventListener("0 6", output));
+
+        bus.onPlayerDeath();
+
+        assertEquals(new ArrayList<>(Arrays.asList(
+                "1 2", "1 5", "0 0", "0 1", "_ 3", "0 6", "-1 4"
+                )),
+                output
+        );
+    }
+
+    private static class TestEventListener implements AbstractGameEventListener {
+        private final String id;
+        private final List<String> output;
+
+        public TestEventListener(String id, List<String> output) {
+            this.id = id;
+            this.output = output;
+        }
+
+        @Override
+        public void onPlayerDeath() { // the only event without an argument ☺
+            output.add(id);
+        }
+    }
+}