Keyboard Controller

import Foundation
import UIKit

class KeyboardController: NSObject {
    
    var viewController: UIViewController
    var constraint: NSLayoutConstraint
    var isKeyboardHidden: Bool {
        return constraint.constant == 0
    }
    
    // MARK: Life Cycle
    
    init(viewController: UIViewController, constraint: NSLayoutConstraint) {
        self.viewController = viewController
        self.constraint = constraint
        super.init()
        self.setupKeyboardObservers()
    }
    
    // MARK: Setup
    
    private func setupKeyboardObservers() {
        self.setupKeyboardWillChangeObserver()
        self.setupDismissKeyboardTapGestureRecognizer()
    }
    
    private func setupKeyboardWillChangeObserver() {
        NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillChange(_:)), name: .UIKeyboardWillChangeFrame, object: nil)
    }
    
    private func setupDismissKeyboardTapGestureRecognizer() {
        let tap = UITapGestureRecognizer(target: self, action: #selector(dismissKeyboard))
        tap.delegate = self
        viewController.view.addGestureRecognizer(tap)
    }
    
    // MARK: Private
    
    func keyboardWillChange(_ notification: Notification) {
        guard let info = notification.userInfo,
            let keyboardFrameValue = info[UIKeyboardFrameEndUserInfoKey] as? NSValue else { return }
        let keyboardFrame: CGRect = keyboardFrameValue.cgRectValue
        constraint.constant = UIScreen.main.bounds.size.height - keyboardFrame.origin.y
        
        if let duration = info[UIKeyboardAnimationDurationUserInfoKey] as? TimeInterval {
            UIView.animate(withDuration: duration, animations: {
                self.viewController.view.layoutIfNeeded()
            })
        } else {
            self.viewController.view.layoutIfNeeded()
        }
    }
    
    func dismissKeyboard() {
        viewController.view.endEditing(true)
    }
    
}

extension KeyboardController: UIGestureRecognizerDelegate {
    
    func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldReceive touch: UITouch) -> Bool {
        return !isKeyboardHidden
    }
    
}