UIViewController+Extensions.swift

import UIKit

extension UIViewController {
    /// method that instantiate a xib file given a string name using Generic
    static func loadFromNib() -> Self {
        func instantiateFromNib<T: UIViewController>() -> T {
            return T.init(nibName: String(describing: T.self), bundle: nil)
        }
        return instantiateFromNib()
    }

    /// method that instantiate a xib file given a string name
    static func instantiate() -> Self {
        return self.init(nibName: String(describing: self), bundle: nil)
    }

    // MARK: Keyboards

    /// hides keyboard when page is tapped. Call it in setupViews()
    func hideKeyboardOnTap() {
        let tap: UITapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(UIViewController.dismissKeyboard))
        tap.cancelsTouchesInView = false
        view.addGestureRecognizer(tap)
    }
    @objc func dismissKeyboard() {
        view.endEditing(true)
    }

    // MARK: Keyboard Notifications

    func registerKeyboardNotifications() {
        NotificationCenter.default.addObserver(self, selector: #selector(keyboardDidShow), name: UIResponder.keyboardDidShowNotification, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillHide), name: UIResponder.keyboardWillHideNotification, object: nil)
    }
    func removeKeyboardNotifications() {
        NotificationCenter.default.removeObserver(self, name: UIResponder.keyboardDidShowNotification, object: nil)
        NotificationCenter.default.removeObserver(self, name: UIResponder.keyboardWillHideNotification, object: nil)
    }
    @objc func keyboardDidShow(notification: NSNotification) {
        guard let keyboardFrame = notification.userInfo![UIResponder.keyboardFrameEndUserInfoKey] as? NSValue else { return }
        let keyboardHeight = view.convert(keyboardFrame.cgRectValue, from: nil).size.height
        scrollView.contentInset.bottom = keyboardHeight + 200
        submitApplicationButton.snp.updateConstraints { (make) in
            make.bottom.equalTo(view.safeAreaLayoutGuide.snp.bottom).offset(-keyboardHeight + 10)
        }
    }
    @objc func keyboardWillHide(notification: NSNotification) {
        scrollView.contentInset.bottom = 0
        submitApplicationButton.snp.updateConstraints { (make) in
            make.bottom.equalTo(view.safeAreaLayoutGuide.snp.bottom).offset(-10)
        }
    }

    // MARK: Alerts

    func presentAlert(title: String, message: String = "") {
        let alertController = UIAlertController(title: title, message: message, preferredStyle: .alert)
        let OKAction = UIAlertAction(title: "OK", style: .default, handler: nil)
        alertController.addAction(OKAction)
        self.present(alertController, animated: true, completion: nil)
    }

    /// Presents an alert with customizable button title and a completion handler
    /// - Parameters:
    ///   - title: Title for alert
    ///   - message: Message for alert
    ///   - options: Button titles separated by comma
    ///   - completion: Returns which options was tapped
    /// - Reference: https://stackoverflow.com/questions/29633938/swift-displaying-alerts-best-practices
    func presentAlertWithOptions(title: String, message: String, options: String..., completion: @escaping (Int) -> Void) {
        let alertController = UIAlertController(title: title, message: message, preferredStyle: .alert)
        if options.count == 0 { // if there is no options, show a basic alert
            let OKAction = UIAlertAction(title: "OK", style: .default, handler: { (action) in
                completion(0)
            })
            alertController.addAction(OKAction)
        } else { // alert with options
            for (index, option) in options.enumerated() {
                var alertStyle = UIAlertAction.Style.default
                switch option { // check if we should style the buttons
                case "Cancel": // cancel style
                    alertStyle = .cancel
                case "Logout", "Discard Changes", "Discard", "Delete", "Remove": // destructive style
                    alertStyle = .destructive
                default: break // keep as default
                }
                alertController.addAction(UIAlertAction(title: option, style: alertStyle, handler: { (action) in
                    completion(index)
                }))
            }
        }
        self.present(alertController, animated: true, completion: nil)
    }

    func presentAlertWithPassword(title: String? = nil,
                                  subtitle: String? = nil,
                                  actionTitle: String? = "Confirm",
                                  cancelTitle: String? = "Cancel",
                                  inputPlaceholder: String? = nil,
                                  inputKeyboardType: UIKeyboardType = UIKeyboardType.default,
                                  cancelHandler: ((UIAlertAction) -> Swift.Void)? = nil,
                                  actionHandler: ((_ text: String?) -> Void)? = nil) {

        let alert = UIAlertController(title: title, message: subtitle, preferredStyle: .alert)
        alert.addTextField { (textField: UITextField) in
            textField.placeholder = inputPlaceholder
            textField.keyboardType = inputKeyboardType
            textField.isSecureTextEntry = true
        }
        alert.addAction(UIAlertAction(title: actionTitle, style: .default, handler: { (action: UIAlertAction) in
            guard let textField = alert.textFields?.first else {
                actionHandler?(nil)
                return
            }
            actionHandler?(textField.text)
        }))
        alert.addAction(UIAlertAction(title: cancelTitle, style: .cancel, handler: cancelHandler))

        self.present(alert, animated: true, completion: nil)
    }
}