Rotate UIViewControllers that conform to a protocol

rotatable.swift

/*
This is an update to an example found on http://www.jairobjunior.com/blog/2016/03/05/how-to-rotate-only-one-view-controller-to-landscape-in-ios-slash-swift/

The code there works, with some updating to the latest Swift, but the pattern isn't very Swifty. The following is what I found to be more helpful.
*/

/*
First, create a protocol that UIViewController's can conform to.
This is in opposition to using `Selector()` and checking for the presence of an empty function.
*/

/// UIViewControllers adopting this protocol will automatically be opted into rotating to all but bottom rotation.
///
/// - Important:
/// You must call resetToPortrait as the view controller is removed from view. Example:
///
/// ```
/// override func viewWillDisappear(_ animated: Bool) {
///   super.viewWillDisappear(animated)
///
///   if isMovingFromParentViewController {
///     resetToPortrait()
///   }
/// }
/// ```
protocol Rotatable: AnyObject {
  func resetToPortrait()
}

extension Rotatable where Self: UIViewController {
  func resetToPortrait() {
    UIDevice.current.setValue(Int(UIInterfaceOrientation.portrait.rawValue), forKey: "orientation")
  }
}

/*
Next, extend AppDelegate to check for VCs that conform to Rotatable. If they do allow device rotation.
Remember, it's up to the conforming VC to reset the device rotation back to portrait.
*/

// MARK: - Device rotation support

extension AppDelegate {
  // The app disables rotation for all view controllers except for a few that opt-in by conforming to the Rotatable protocol
  func application(_ application: UIApplication, supportedInterfaceOrientationsFor window: UIWindow?) -> UIInterfaceOrientationMask {
    guard
      let _ = topViewController(for: window?.rootViewController) as? Rotatable
      else { return .portrait }

      return .allButUpsideDown
  }

  private func topViewController(for rootViewController: UIViewController!) -> UIViewController? {
    guard let rootVC = rootViewController else { return nil }

    if rootVC is UITabBarController {
      let rootTabBarVC = rootVC as! UITabBarController

      return topViewController(for: rootTabBarVC.selectedViewController)
    } else if rootVC is UINavigationController {
      let rootNavVC = rootVC as! UINavigationController

      return topViewController(for: rootNavVC.visibleViewController)
    } else if let rootPresentedVC = rootVC.presentedViewController {
      return topViewController(for: rootPresentedVC)
    }

    return rootViewController
  }
}