Convert IdleDetector to TypeScript

ts/IdleDetector.ts

@@ -0,0 +1,55 @@
+// Copyright 2018-2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import EventEmitter from 'events';
+import * as log from './logging/log';
+
+const POLL_INTERVAL_MS = 5 * 1000;
+const IDLE_THRESHOLD_MS = 20;
+
+export class IdleDetector extends EventEmitter {
+  private handle: undefined | ReturnType<typeof requestIdleCallback>;
+  private timeoutId: undefined | ReturnType<typeof setTimeout>;
+
+  public start(): void {
+    log.info('Start idle detector');
+    this.scheduleNextCallback();
+  }
+
+  public stop(): void {
+    if (!this.handle) {
+      return;
+    }
+
+    log.info('Stop idle detector');
+    this.clearScheduledCallbacks();
+  }
+
+  private clearScheduledCallbacks() {
+    if (this.handle) {
+      cancelIdleCallback(this.handle);
+      delete this.handle;
+    }
+
+    if (this.timeoutId) {
+      clearTimeout(this.timeoutId);
+      delete this.timeoutId;
+    }
+  }
+
+  private scheduleNextCallback() {
+    this.clearScheduledCallbacks();
+    this.handle = window.requestIdleCallback(deadline => {
+      const { didTimeout } = deadline;
+      const timeRemaining = deadline.timeRemaining();
+      const isIdle = timeRemaining >= IDLE_THRESHOLD_MS;
+      this.timeoutId = setTimeout(
+        () => this.scheduleNextCallback(),
+        POLL_INTERVAL_MS
+      );
+      if (isIdle || didTimeout) {
+        this.emit('idle', { timestamp: Date.now(), didTimeout, timeRemaining });
+      }
+    });
+  }
+}