add cooldown timer

ts/editable/cooldown-timer.ts

@@ -0,0 +1,31 @@
+// Copyright: Ankitects Pty Ltd and contributors
+// License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
+
+export class CooldownTimer {
+    private executing = false;
+    private queuedAction: (() => void) | null = null;
+    private delay: number;
+
+    constructor(delayMs: number) {
+        this.delay = delayMs;
+    }
+
+    schedule(action: () => void): void {
+        if (this.executing) {
+            this.queuedAction = action;
+        } else {
+            this.executing = true;
+            action();
+            setTimeout(this.#pop.bind(this), this.delay);
+        }
+    }
+
+    #pop(): void {
+        this.executing = false;
+        if (this.queuedAction) {
+            const action = this.queuedAction;
+            this.queuedAction = null;
+            this.schedule(action);
+        }
+    }
+}