struct DeviceTokenHandler: RemoteNotificationDeviceTokenHandling {    
}

extension AppDelegate { // RemoteNotificationDeviceTokenHandling
    func application(_ application: UIApplication, didRegisterForRemoteNotificationsWithDeviceToken deviceToken: Data) {
        RemoteNotificationManager.shared.deviceTokenHandler.application(application, didRegisterForRemoteNotificationsWithDeviceToken: deviceToken)
    }

    func application(_ application: UIApplication, didFailToRegisterForRemoteNotificationsWithError error: Error) {
        RemoteNotificationManager.shared.deviceTokenHandler.application(application, didFailToRegisterForRemoteNotificationsWithError: error)
    }
}

struct DeviceTokenHandler: RemoteNotificationDeviceTokenHandling {    
    func didRegisterForRemoteNotifications(result: DeviceTokenResult) {
        switch result {
        case .success(let deviceToken):
            print("Success deviceToken.string: \(deviceToken.string)")
        case .failure(let error):
            print("Failure error: \(error)")
        }
    }
}

extension Notification.Name {
    public struct RemoteNotificationDeviceTokenHandling {
        public static let didRegisterForRemoteNotifications = Notification.Name(rawValue: "RemoteNotificationDeviceTokenHandling.didRegisterForRemoteNotifications")
        public static let didFailToRegisterForRemoteNotifications = Notification.Name(rawValue: "RemoteNotificationDeviceTokenHandling.didFailToRegisterForRemoteNotifications")
    }    
}

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    UNUserNotificationCenter.current().delegate = self
    return true
}

extension AppDelegate: UNUserNotificationCenterDelegate {
    func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Swift.Void) {
        print("Payload: \(Payload(notification)")
        completionHandler([.badge, .sound, .alert])
    }

    func userNotificationCenter(_ center: UNUserNotificationCenter, didReceive response: UNNotificationResponse, withCompletionHandler completionHandler: @escaping () -> Swift.Void) {
        print("Payload: \(Payload(response)")
        completionHandler()
    }
}

class iOS9AndBelowRemoteNotificationHandler: iOS9AndBelowRemoteNotificationHandling {    
    let didReceiveRemoteNotificationHandlers = WeakContainer<iOS9AndBelowRemoteNotificationPayloadHandling>()
}

extension AppDelegate { // iOS9AndBelowRemoteNotificationHandling
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        RemoteNotificationManager.shared.iOS9AndBelowHandler?.application(application, didFinishLaunchingWithOptions: launchOptions)        
        return true
    }

    func application(_ application: UIApplication, didRegister notificationSettings: UIUserNotificationSettings) {
        RemoteNotificationManager.shared.iOS9AndBelowHandler?.application(application, didRegister: notificationSettings)
    }

    /// - note: Opening the app by tapping the icon will never give you information about previous notifications. It's only if you actually open the app via a notification that you will be able to access the notification data. (from [Stackoverflow](https://stackoverflow.com/a/13847840))
    func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable : Any]) {
        RemoteNotificationManager.shared.iOS9AndBelowHandler?.application(application, didReceiveRemoteNotification: userInfo)
    }
}

iOS9AndBelowHandler.didReceiveRemoteNotificationHandlers.add(self)

extension ViewController: iOS9AndBelowRemoteNotificationPayloadHandling {
    func didReceiveRemoteNotificationPayload(_ payload: Payload) {
        print("Payload: \(payload)")
    }
}

extension Notification.Name {
    public struct RemoteNotificationHandling {
        @available(iOS, deprecated: 10.0)
        public static let didReceiveRemoteNotification = Notification.Name(rawValue: "RemoteNotificationHandling.didReceiveRemoteNotification")
    }
}