[MM 7970] Maintain online status while the Desktop App is in the background ... and other things. (#993)

* monitor os-level user activity

* disable eslint warnings

* add tests for UserActivityMonitor

* couple more tests

* udpate headers of new files

test/specs/main/user_activity_monitor_test.js

@@ -0,0 +1,89 @@
+// Copyright (c) 2016-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+import assert from 'assert';
+
+import UserActivityMonitor from '../../../src/main/UserActivityMonitor';
+
+describe('UserActivityMonitor', () => {
+  describe('updateIdleTime', () => {
+    it('should set idle time to provided value', () => {
+      const userActivityMonitor = new UserActivityMonitor();
+      const idleTime = Math.round(Date.now() / 1000);
+      userActivityMonitor.updateIdleTime(idleTime);
+      assert.equal(userActivityMonitor.userIdleTime, idleTime);
+    });
+  });
+
+  describe('updateUserActivityStatus', () => {
+    let userActivityMonitor;
+
+    beforeEach(() => {
+      userActivityMonitor = new UserActivityMonitor();
+    });
+
+    it('should set user status to active', () => {
+      userActivityMonitor.updateUserActivityStatus(true);
+      assert.equal(userActivityMonitor.userIsActive, true);
+    });
+    it('should set user status to inactive', () => {
+      userActivityMonitor.updateUserActivityStatus(false);
+      assert.equal(userActivityMonitor.userIsActive, false);
+    });
+  });
+
+  describe('handleSystemGoingAway', () => {
+    it('should set user status to inactive and forceInactive to true', () => {
+      const userActivityMonitor = new UserActivityMonitor();
+      userActivityMonitor.isActive = true;
+      userActivityMonitor.forceInactive = false;
+      userActivityMonitor.handleSystemGoingAway();
+      assert.equal(!userActivityMonitor.userIsActive && userActivityMonitor.forceInactive, true);
+    });
+  });
+
+  describe('handleSystemComingBack', () => {
+    it('should set user status to active and forceInactive to false', () => {
+      const userActivityMonitor = new UserActivityMonitor();
+      userActivityMonitor.isActive = false;
+      userActivityMonitor.forceInactive = true;
+      userActivityMonitor.handleSystemComingBack();
+      assert.equal(userActivityMonitor.userIsActive && !userActivityMonitor.forceInactive, true);
+    });
+  });
+
+  describe('sendStatusUpdate', () => {
+    let userActivityMonitor;
+
+    beforeEach(() => {
+      userActivityMonitor = new UserActivityMonitor();
+    });
+
+    it('should emit a non-system triggered status event indicating a user is active', () => {
+      userActivityMonitor.on('status', ({userIsActive, isSystemEvent}) => {
+        assert.equal(userIsActive && !isSystemEvent, true);
+      });
+      userActivityMonitor.updateUserActivityStatus(true, false);
+    });
+
+    it('should emit a non-system triggered status event indicating a user is inactive', () => {
+      userActivityMonitor.on('status', ({userIsActive, isSystemEvent}) => {
+        assert.equal(!userIsActive && !isSystemEvent, true);
+      });
+      userActivityMonitor.updateUserActivityStatus(false, false);
+    });
+
+    it('should emit a system triggered status event indicating a user is active', () => {
+      userActivityMonitor.on('status', ({userIsActive, isSystemEvent}) => {
+        assert.equal(userIsActive && isSystemEvent, true);
+      });
+      userActivityMonitor.updateUserActivityStatus(true, true);
+    });
+
+    it('should emit a system triggered status event indicating a user is inactive', () => {
+      userActivityMonitor.on('status', ({userIsActive, isSystemEvent}) => {
+        assert.equal(!userIsActive && isSystemEvent, true);
+      });
+      userActivityMonitor.updateUserActivityStatus(false, true);
+    });
+  });
+});