extension UIApplication {
	class func topViewController(base: UIViewController? = UIApplication.shared.keyWindow?.rootViewController) -> UIViewController? {
		if let nav = base as? UINavigationController {
			return topViewController(base: nav.visibleViewController)
		}
		if let tab = base as? UITabBarController {
			if let selected = tab.selectedViewController {
				return topViewController(base: selected)
			}
		}
		if let presented = base?.presentedViewController {
			return topViewController(base: presented)
		}

		if let vc = base as? NotificationShowable {
			return base
		}
		return nil

	}
}