[Mainline Feature] Transient events support

src/main/java/cam72cam/mod/event/Event.java

@@ -6,22 +6,26 @@
 import java.util.function.Function;
 
 public class Event<T> {
-    private final Set<Runnable> pre = new LinkedHashSet<>();
-    private final Set<T> callbacks = new LinkedHashSet<>();
-    private final Set<Runnable> post = new LinkedHashSet<>();
+    final Set<Runnable> pre = new LinkedHashSet<>();
+    final Set<T> callbacks = new LinkedHashSet<>();
+    final Set<Runnable> post = new LinkedHashSet<>();
 
     public void pre(Runnable callback) {
         pre.add(callback);
     }
+
     public void subscribe(T callback) {
         callbacks.add(callback);
     }
+
     public void post(Runnable callback) {
         post.add(callback);
     }
+
     void execute(Consumer<T> handler) {
         pre.forEach(Runnable::run);
         callbacks.forEach(handler);
+
         post.forEach(Runnable::run);
     }
 
@@ -35,4 +39,21 @@ boolean executeCancellable(Function<T, Boolean> handler) {
         post.forEach(Runnable::run);
         return true;
     }
+
+    /**
+     * For those events fired multiple times and should be handled respectively
+     */
+    static class TransientEvent<T> extends Event<T> {
+        @Override
+        void execute(Consumer<T> handler) {
+            super.execute(handler);
+            callbacks.clear();
+        }
+
+        boolean executeCancellable(Function<T, Boolean> handler) {
+            boolean result = super.executeCancellable(handler);
+            callbacks.clear();
+            return result;
+        }
+    }
 }