import UIKit

final public class KeyboardObserving {

    public typealias ChangeSet = (keyboardRect: CGRect, animationCurve: UIView.AnimationOptions, duration: Double)

    public var onKeyboardWillShow: ((ChangeSet) -> Void)?
    public var onKeyboardWillHide: ((ChangeSet) -> Void)?

    public init() {
        registerKeyboardNotification()
    }

    deinit {
        removeKeyboardObservers()
    }

    public func removeKeyboardObservers() {
       NotificationCenter.default.removeObserver(self)
    }

    public func registerKeyboardNotification() {
       removeKeyboardObservers() // this should prevent from observing keyboard change twice.

       NotificationCenter.default.addObserver(self, selector: #selector(self.keyboardWillShow(_:)), name: UIResponder.keyboardWillShowNotification, object: nil)
       NotificationCenter.default.addObserver(self, selector: #selector(self.keyboardWillHide(_:)), name: UIResponder.keyboardWillHideNotification, object: nil)
    }

    // MARK: - Keyboard
    // MARK: will show
    @objc private func keyboardWillShow(_ notification: Notification) {
        guard
           let keyboardRect = (notification.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue,
           let duration = notification.userInfo?[UIResponder.keyboardAnimationDurationUserInfoKey] as? NSNumber,
           let curve = notification.userInfo?[UIResponder.keyboardAnimationCurveUserInfoKey] as? NSNumber
           else { return }

        onKeyboardWillShow?((keyboardRect, UIView.AnimationOptions(rawValue: curve.uintValue), duration.doubleValue))
    }

    // MARK: will hide
    @objc private func keyboardWillHide(_ notification: Notification) {
        guard
           let keyboardRect = (notification.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue,
           let duration = notification.userInfo?[UIResponder.keyboardAnimationDurationUserInfoKey] as? NSNumber,
           let curve = notification.userInfo?[UIResponder.keyboardAnimationCurveUserInfoKey] as? NSNumber
           else { return }

        onKeyboardWillShow?((keyboardRect, UIView.AnimationOptions(rawValue: curve.uintValue), duration.doubleValue))
    }
}


class ViewController: UIViewController {

    private let keyboardObserving = KeyboardObserving()

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        keyboardObserving.onKeyboardWillShow = { change in
            print("show", change)
        }

        keyboardObserving.onKeyboardWillHide = { change in
            print("hide", change)
        }
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

}