feat: RegisterEventForGamemode util function

scripts/util/register-event-for-gamemodes.ts

@@ -0,0 +1,52 @@
+/**
+ * Pass an event that should be only registered when playing certain gamemodes.
+ *
+ * This function will register/unregister the provided events handler when gamemodes change.
+ *
+ * It returns a function that will clean up both event handlers. It's unlikely we'll ever need to use it,
+ * so usually you can just discard it.
+ *
+ * @example
+ * ```ts
+ * // In the static initializer block for some panel's class, call the onUpdate function on this class
+ * // whenever the 'HudProcessInput' event is fired, ONLY if the current gamemode is Gamemode.DEFRAG.
+ * 	static {
+ * 		RegisterEventForGamemodes(
+ * 			[GameMode.DEFRAG],
+ * 			'HudProcessInput',
+ * 			$.GetContextPanel(),
+ * 			this.onUpdate.bind(this)
+ * 		);
+ * 	}
+ * ```
+ * @param gamemodes - Gamemodes to register the callback for. Handler is unregistered for any other modes.
+ * @param event - Event name
+ * @param context - Panel context
+ * @param callbackFn - Event callback
+ * @returns Cleanup function that unregisters both event handlers
+ */
+function RegisterEventForGamemodes(
+	gamemodes: number[],
+	event: string,
+	context: string | Panel,
+	callbackFn: (...args: unknown[]) => void
+): () => void {
+	let innerHandle: number | undefined;
+	const outerHandle = $.RegisterForUnhandledEvent('LevelInitPostEntity', () => {
+		// @ts-expect-error - TODO: Typings for this API
+		if (!innerHandle && gamemodes.includes(GameModeAPI.GetCurrentGameMode())) {
+			innerHandle = $.RegisterEventHandler(event, context, callbackFn);
+		} else if (innerHandle) {
+			$.UnregisterEventHandler(event, context, innerHandle);
+			innerHandle = undefined;
+		}
+	});
+
+	return () => {
+		if (innerHandle) {
+			$.UnregisterEventHandler(event, context, innerHandle);
+		}
+
+		$.UnregisterForUnhandledEvent('LevelInitPostEntity', outerHandle);
+	};
+}