func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
// Use Firebase library to configure APIs
FirebaseApp.configure()
self.registerForPushNotifications(application: application)
Messaging.messaging().delegate = self

    if let token = InstanceID.instanceID().token() {
        NSLog("FCM TOKEN : \(token)")
        DataModel.sharedInstance.onSetUserFCMStringToken(FCM: token)
        self.connectToFcm()
    }
    if launchOptions != nil {
        //opened from a push notification when the app is closed
        _ = launchOptions?[UIApplicationLaunchOptionsKey.remoteNotification] as? [AnyHashable: Any] ?? [AnyHashable: Any]()
    }
    else {
        //opened app without a push notification.
    }
    return true
}

@available（iOS 10，*）

extension AppDelegate: UNUserNotificationCenterDelegate {
// iOS10+, called when presenting notification in foreground
func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {
    let userInfo = notification.request.content.userInfo
    NSLog("[UserNotificationCenter] willPresentNotification: \(userInfo)")
    //TODO: Handle foreground notification
    completionHandler([.alert])
}

// iOS10+, called when received response (default open, dismiss or custom action) for a notification
func userNotificationCenter(_ center: UNUserNotificationCenter, didReceive response: UNNotificationResponse, withCompletionHandler completionHandler: @escaping () -> Void) {
    let userInfo = response.notification.request.content.userInfo
    NSLog("[UserNotificationCenter] didReceiveResponse: \(userInfo)")
    //TODO: Handle background notification
    completionHandler()
}}

extension AppDelegate : MessagingDelegate {
//MARK: FCM Token Refreshed
func messaging(_ messaging: Messaging, didRefreshRegistrationToken fcmToken: String) {
    NSLog("[RemoteNotification] didRefreshRegistrationToken: \(fcmToken)")
}

// Receive data message on iOS 10 devices while app is in the foreground.
func messaging(_ messaging: Messaging, didReceive remoteMessage: MessagingRemoteMessage) {
    NSLog("remoteMessage: \(remoteMessage.appData)")
}}

//Register for push notification.
func registerForPushNotifications(application: UIApplication) {
    if #available(iOS 10.0, *) {
        let center  = UNUserNotificationCenter.current()
        center.delegate = self
        center.requestAuthorization(options: [.alert,.sound]) { (granted, error) in
            if error == nil{
                DispatchQueue.main.async(execute: {
                    application.registerForRemoteNotifications()
                })
            }
        }
    }
    else {

        let settings = UIUserNotificationSettings(types: [.alert,.sound], categories: nil)
        application.registerUserNotificationSettings(settings)
        application.registerForRemoteNotifications()
    }

    // Add observer for InstanceID token refresh callback.
    NotificationCenter.default.addObserver(self, selector: #selector(self.tokenRefreshNotification), name: NSNotification.Name.InstanceIDTokenRefresh, object: nil)

}

@objc func tokenRefreshNotification(_ notification: Notification) {
    print(#function)
    if let refreshedToken = InstanceID.instanceID().token() {
        NSLog("Notification: refresh token from FCM -> \(refreshedToken)")

    }
    // Connect to FCM since connection may have failed when attempted before having a token.
    connectToFcm()
}

func connectToFcm() {
    // Won't connect since there is no token
    guard InstanceID.instanceID().token() != nil else {
        NSLog("FCM: Token does not exist.")
        return
    }

    Messaging.messaging().shouldEstablishDirectChannel = true
}

func application(_ application: UIApplication, didFailToRegisterForRemoteNotificationsWithError error: Error) {
    NSLog("Notification: Unable to register for remote notifications: \(error.localizedDescription)")
}


// This function is added here only for debugging purposes, and can be removed if swizzling is enabled.
// If swizzling is disabled then this function must be implemented so that the APNs token can be paired to the InstanceID token.
func application(_ application: UIApplication, didRegisterForRemoteNotificationsWithDeviceToken deviceToken: Data) {


    Messaging.messaging().apnsToken = deviceToken


}

// iOS9, called when presenting notification in foreground
func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable : Any]) {
    NSLog("didReceiveRemoteNotification for iOS9: \(userInfo)")

}

func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable: Any], fetchCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void) {




}