Add a simple callback decorator to behavior tree

src/main/java/net/citizensnpcs/api/ai/tree/Callback.java

@@ -0,0 +1,44 @@
+package net.citizensnpcs.api.ai.tree;
+
+import java.util.function.Consumer;
+
+/**
+ * Wraps an {@link Behavior} and runs callbacks when the underlying Behavior is finished.
+ */
+public class Callback extends BehaviorGoalAdapter {
+    private final Consumer<BehaviorStatus> cb;
+    private final Behavior wrapping;
+
+    private Callback(Behavior wrapping, Consumer<BehaviorStatus> cb) {
+        this.wrapping = wrapping;
+        this.cb = cb;
+    }
+
+    @Override
+    public void reset() {
+        wrapping.reset();
+    }
+
+    @Override
+    public BehaviorStatus run() {
+        BehaviorStatus status = wrapping.run();
+        switch (status) {
+            case FAILURE:
+            case SUCCESS:
+            case RESET_AND_REMOVE:
+                cb.accept(status);
+            default:
+                break;
+        }
+        return status;
+    }
+
+    @Override
+    public boolean shouldExecute() {
+        return wrapping.shouldExecute();
+    }
+
+    public static Callback callback(Behavior wrapping, Consumer<BehaviorStatus> cb) {
+        return new Callback(wrapping, cb);
+    }
+}