class ViewController: UIViewController {
	
	typealias CompletionHandler = (_ success: Bool, _ error: Error?) -> Void
	
	private var mNotificationsEnabled = false

	override func viewDidLoad() {
		super.viewDidLoad()
		
		FirebaseApp.configure()
	}

	@IBAction func ButtonPressed(_ sender: UIButton) {
		mNotificationsEnabled = !mNotificationsEnabled
		let newTitle = mNotificationsEnabled ? "Disable Notifications" : "Enable Notifications"
		sender.setTitle(newTitle, for: .normal)
		sender.isEnabled = false
		
		setNotifications(enabled: mNotificationsEnabled, completionHandler: { (success, error) in
			sender.isEnabled = true
		})
	}
	
	func setNotifications(enabled: Bool, completionHandler: @escaping CompletionHandler) {
		if (enabled) {
			enableNotifications(completionHandler: {(success, error) in
				self.getToken(completionHandler)
			})
		}
		else {
			disableNotifications(completionHandler: completionHandler)
		}
	}
	
	func enableNotifications(completionHandler: @escaping CompletionHandler) {
		print("Enabling...")
		
		let notificationCenter = UNUserNotificationCenter.current()
		notificationCenter.requestAuthorization(options: [.alert, .sound, .badge], completionHandler: {(success, error) in
			if (success) {
				notificationCenter.delegate = self;
				Messaging.messaging().delegate = self
				
				DispatchQueue.main.async(execute: {
					UIApplication.shared.registerForRemoteNotifications() // Must run on main thread
					print("Notifications Enabled")
					completionHandler(success, error)
				})
				
			}
			else {
				print("Enabling failed")
				completionHandler(false, error)
			}
		})
	}
	
	func disableNotifications(completionHandler: @escaping CompletionHandler) {
		print("Disabling...")
		
		DispatchQueue.main.async(execute: {
			UIApplication.shared.unregisterForRemoteNotifications() // Must run on main thread
			print("Notifications Disabled")
			completionHandler(true, nil)
		})
	}
	
	func getToken(_ completionHandler: @escaping CompletionHandler) {
		print("Fetching Token...")
		
		//MARK: BUG? The following never calls its handler if invoked after unregisterForRemoteNotifications() has been called twice.
		InstanceID.instanceID().instanceID(handler: { (result, error) in
			if let error = error {
				print("Error fetching remote instance ID: \(error)")
				completionHandler(false, error)
			}
			else if let result = result {
				print("Token found")
				completionHandler(true, nil)
			}
		})
	}
	
}