// embed FirstVC as the Root View Controller of a Navigation Controller

class FirstVC: UIViewController {
	
	override func viewDidLoad() {
		super.viewDidLoad()
		
		view.backgroundColor = .yellow
		
		let button = UIButton(type: .system, primaryAction: UIAction(title: "Push to Second VC", handler: { _ in
			let vc = SecondVC()
			self.navigationController?.pushViewController(vc, animated: true)
		}))
		view.addSubview(button)
		button.translatesAutoresizingMaskIntoConstraints = false
		NSLayoutConstraint.activate([
			button.centerXAnchor.constraint(equalTo: view.centerXAnchor),
			button.centerYAnchor.constraint(equalTo: view.centerYAnchor)
		])
		
	}
	
}

class SecondVC: UIViewController {
	
	override func viewDidLoad() {
		super.viewDidLoad()
		
		view.backgroundColor = .green
		
		let button = UIButton(type: .system, primaryAction: UIAction(title: "Push to Third VC", handler: { _ in
			let vc = ThirdVC()
			self.navigationController?.pushViewController(vc, animated: true)
		}))
		view.addSubview(button)
		button.translatesAutoresizingMaskIntoConstraints = false
		NSLayoutConstraint.activate([
			button.centerXAnchor.constraint(equalTo: view.centerXAnchor),
			button.centerYAnchor.constraint(equalTo: view.centerYAnchor)
		])
		
	}
	
}

class ThirdVC: UIViewController {
	
	override func viewDidLoad() {
		super.viewDidLoad()
		
		view.backgroundColor = .cyan
		
		let v = UILabel()
		v.text = "This is Third VC"
		view.addSubview(v)
		v.translatesAutoresizingMaskIntoConstraints = false
		NSLayoutConstraint.activate([
			v.centerXAnchor.constraint(equalTo: view.centerXAnchor),
			v.centerYAnchor.constraint(equalTo: view.centerYAnchor)
		])
		
		
		if let navC = self.navigationController {
			var a = navC.viewControllers
			a.remove(at: 1)
			navC.setViewControllers(a, animated: false)
		}
	}
	
}