Add activity tracker

js/plugin/activity.ts

@@ -0,0 +1,40 @@
+export const ActivityMixin = (SuperClass) => {
+  return class ActivityMixinClass extends SuperClass {
+    activityTriggered = false;
+    _activityCooldown = 15000;
+    _activityTimeout;
+    constructor() {
+      super();
+      for (const ev of ["pointerdown", "pointermove", "keydown"]) {
+        window.addEventListener(ev, () => this.activityTrigger());
+      }
+      this.addEventListener("fully-update", () => {
+        this.activityTrigger();
+      });
+    }
+
+    activityTrigger() {
+      if (!this.activityTriggered) {
+        this.sendUpdate({
+          activity: true,
+        });
+      }
+      this.activityTriggered = true;
+      clearTimeout(this._activityTimeout);
+      this._activityTimeout = setTimeout(
+        () => this.activityReset(),
+        this._activityCooldown
+      );
+    }
+
+    activityReset() {
+      clearTimeout(this._activityTimeout);
+      if (this.activityTriggered) {
+        this.sendUpdate({
+          activity: false,
+        });
+      }
+      this.activityTriggered = false;
+    }
+  };
+};