[Swift 3] Visible UIViewController

visibleViewController.swift

extension UIApplication {
    class func visibleViewController(base: UIViewController? = UIApplication.sharedApplication().keyWindow?.rootViewController) -> UIViewController? {

        if let nav = base as? UINavigationController {
            return visibleViewController(nav.visibleViewController)
        }

        if let tab = base as? UITabBarController {
            let moreNavigationController = tab.moreNavigationController

            if let top = moreNavigationController.topViewController where top.view.window != nil {
                return visibleViewController(top)
            } else if let selected = tab.selectedViewController {
                return visibleViewController(selected)
            }
        }

        if let presented = base?.presentedViewController {
            return visibleViewController(presented)
        }
        return base
    }
}