Improve window activity detection, improving notification delivery

ts/services/ActiveWindowService.ts

@@ -0,0 +1,97 @@
+// Copyright 2020 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { throttle } from 'lodash';
+
+// Idle timer - you're active for ACTIVE_TIMEOUT after one of these events
+const ACTIVE_TIMEOUT = 15 * 1000;
+const LISTENER_THROTTLE_TIME = 5 * 1000;
+const ACTIVE_EVENTS = [
+  'click',
+  'keydown',
+  'mousedown',
+  'mousemove',
+  // 'scroll', // this is triggered by Timeline re-renders, can't use
+  'touchstart',
+  'wheel',
+];
+
+export class ActiveWindowService {
+  // This starting value might be wrong but we should get an update from the main process
+  //  soon. We'd rather report that the window is inactive so we can show notifications.
+  private isInitialized = false;
+
+  private isFocused = false;
+
+  private activeCallbacks: Array<() => void> = [];
+
+  private lastActiveEventAt = -Infinity;
+
+  private callActiveCallbacks: () => void;
+
+  constructor() {
+    this.callActiveCallbacks = throttle(() => {
+      this.activeCallbacks.forEach(callback => callback());
+    }, LISTENER_THROTTLE_TIME);
+  }
+
+  // These types aren't perfectly accurate, but they make this class easier to test.
+  initialize(document: EventTarget, ipc: NodeJS.EventEmitter): void {
+    if (this.isInitialized) {
+      throw new Error(
+        'Active window service should not be initialized multiple times'
+      );
+    }
+    this.isInitialized = true;
+
+    this.lastActiveEventAt = Date.now();
+
+    const onActiveEvent = this.onActiveEvent.bind(this);
+    ACTIVE_EVENTS.forEach((eventName: string) => {
+      document.addEventListener(eventName, onActiveEvent, true);
+    });
+
+    // We don't know for sure that we'll get the right data over IPC so we use `unknown`.
+    ipc.on('set-window-focus', (_event: unknown, isFocused: unknown) => {
+      this.setWindowFocus(Boolean(isFocused));
+    });
+  }
+
+  isActive(): boolean {
+    return (
+      this.isFocused && Date.now() < this.lastActiveEventAt + ACTIVE_TIMEOUT
+    );
+  }
+
+  registerForActive(callback: () => void): void {
+    this.activeCallbacks.push(callback);
+  }
+
+  unregisterForActive(callback: () => void): void {
+    this.activeCallbacks = this.activeCallbacks.filter(
+      item => item !== callback
+    );
+  }
+
+  private onActiveEvent(): void {
+    this.updateState(() => {
+      this.lastActiveEventAt = Date.now();
+    });
+  }
+
+  private setWindowFocus(isFocused: boolean): void {
+    this.updateState(() => {
+      this.isFocused = isFocused;
+    });
+  }
+
+  private updateState(fn: () => void): void {
+    const wasActiveBefore = this.isActive();
+    fn();
+    const isActiveNow = this.isActive();
+
+    if (!wasActiveBefore && isActiveNow) {
+      this.callActiveCallbacks();
+    }
+  }
+}