encapsulating the user code_4.swift

enum UserInteractionError: Error {
    case userCanceled
}

extension UIViewController
{
    func choiceIndexUsingActionSheet(title: String, message: String, choices: [String], onSourceView view: UIView) -> Promise<Int> {
        return Promise(queue: DispatchQueue.main) { fulfill, reject in
            let alert = UIAlertController(title: title.isEmpty ? nil : title, message: message.isEmpty ? nil : message, preferredStyle: .actionSheet)

            let cancelAction = UIAlertAction(title: "Cancel", style: .cancel, handler: { _ in reject(UserInteractionError.userCanceled) })

            let actions = choices.enumerated().map { offset, element in
                UIAlertAction(title: element, style: .default, handler: { _ in fulfill(offset) })
            }
            
            for action in actions + [cancelAction] {
                alert.addAction(action)
            }
            
            if let popoverPresentationController = alert.popoverPresentationController {
                popoverPresentationController.sourceView = view
                popoverPresentationController.sourceRect = view.bounds
            }
            self.present(alert, animated: true, completion: nil)
        }
    }
}