fix(preview-api): raise deviceLost event after timeout of 5 seconds

In case when some `.js` file is changed, preview app is restarted on device e.g preview app is stopped and started again. When the preview app is stopped, Pubnub reports the device as lost and when preview app is started, Pubnub reports the device as found. With this fix, we want to delay the emitting of deviceLost event. This way we'll give a chance to find the device before reporting it as lost.

Author: Fatme

lib/services/livesync/playground/devices/preview-devices-service.ts

@@ -4,6 +4,7 @@ import { DeviceDiscoveryEventNames, DEVICE_LOG_EVENT_NAME } from "../../../../co
 
 export class PreviewDevicesService extends EventEmitter implements IPreviewDevicesService {
 	private connectedDevices: Device[] = [];
+	private deviceTimers: IDictionary<NodeJS.Timer> = {};
 
 	constructor(private $previewAppLogProvider: IPreviewAppLogProvider,
 		private $previewAppPluginsService: IPreviewAppPluginsService) {
@@ -23,7 +24,7 @@ export class PreviewDevicesService extends EventEmitter implements IPreviewDevic
 
 		_(this.connectedDevices)
 			.reject(d => _.find(devices, device => d.id === device.id))
-			.each(device => this.raiseDeviceLost(device));
+			.each(device => this.raiseDeviceLostAfterTimeout(device));
 	}
 
 	public getDeviceById(id: string): Device {
@@ -45,6 +46,10 @@ export class PreviewDevicesService extends EventEmitter implements IPreviewDevic
 	}
 
 	private raiseDeviceFound(device: Device) {
+		if (this.deviceTimers[device.id]) {
+			clearTimeout(this.deviceTimers[device.id]);
+		}
+
 		this.emit(DeviceDiscoveryEventNames.DEVICE_FOUND, device);
 		this.connectedDevices.push(device);
 	}
@@ -53,5 +58,15 @@ export class PreviewDevicesService extends EventEmitter implements IPreviewDevic
 		this.emit(DeviceDiscoveryEventNames.DEVICE_LOST, device);
 		_.remove(this.connectedDevices, d => d.id === device.id);
 	}
+
+	private raiseDeviceLostAfterTimeout(device: Device) {
+		if (!this.deviceTimers[device.id]) {
+			const timeoutId = setTimeout(() => {
+				this.raiseDeviceLost(device);
+				clearTimeout(timeoutId);
+			}, 5 * 1000);
+			this.deviceTimers[device.id] = timeoutId;
+		}
+	}
 }
 $injector.register("previewDevicesService", PreviewDevicesService);