class MoveImageScrollVC: UIViewController, UIScrollViewDelegate {
	
	var exampleConstraint: NSLayoutConstraint!
	
	override func viewDidLoad() {
		super.viewDidLoad()
		
		let scrollView = UIScrollView()
		scrollView.backgroundColor = .systemYellow
		scrollView.translatesAutoresizingMaskIntoConstraints = false
		view.addSubview(scrollView)
		
		let g = view.safeAreaLayoutGuide
		let cg = scrollView.contentLayoutGuide
		let fg = scrollView.frameLayoutGuide
		
		NSLayoutConstraint.activate([
			// constrain scroll view to safe area, inset by 20-points
			scrollView.topAnchor.constraint(equalTo: g.topAnchor, constant: 20.0),
			scrollView.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 20.0),
			scrollView.bottomAnchor.constraint(equalTo: g.bottomAnchor, constant: -20.0),
			scrollView.widthAnchor.constraint(equalToConstant: 100.0),
		])
		
		let tallLabel = UILabel()
		tallLabel.backgroundColor = .cyan
		tallLabel.numberOfLines = 0
		tallLabel.textAlignment = .center
		tallLabel.font = .systemFont(ofSize: 24.0, weight: .light)
		
		var str: String = "1"
		for i in 2...50 {
			str += "\n\(i)"
		}
		tallLabel.text = str
		
		tallLabel.translatesAutoresizingMaskIntoConstraints = false
		scrollView.addSubview(tallLabel)
		
		NSLayoutConstraint.activate([
			tallLabel.topAnchor.constraint(equalTo: cg.topAnchor, constant: 8.0),
			tallLabel.leadingAnchor.constraint(equalTo: cg.leadingAnchor, constant: 8.0),
			tallLabel.trailingAnchor.constraint(equalTo: cg.trailingAnchor, constant: 0.0),
			tallLabel.bottomAnchor.constraint(equalTo: cg.bottomAnchor, constant: -8.0),
			tallLabel.widthAnchor.constraint(equalTo: fg.widthAnchor, constant: -16.0),
		])
		
		let anchorView = UILabel()
		anchorView.backgroundColor = .yellow
		anchorView.textAlignment = .center
		anchorView.text = "Anchor View"

		let constrainedView = UIImageView()
		if let img = UIImage(named: "sampleImage") {
			constrainedView.image = img
		}
		
		anchorView.translatesAutoresizingMaskIntoConstraints = false
		view.addSubview(anchorView)
		constrainedView.translatesAutoresizingMaskIntoConstraints = false
		view.addSubview(constrainedView)
		
		exampleConstraint = constrainedView.bottomAnchor.constraint(equalTo: anchorView.topAnchor, constant: 0.0)
		exampleConstraint.priority = .required - 1
		
		NSLayoutConstraint.activate([
			
			anchorView.leadingAnchor.constraint(equalTo: scrollView.trailingAnchor, constant: 20.0),
			anchorView.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: -20.0),
			anchorView.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor, constant: 0.0),
			anchorView.heightAnchor.constraint(equalToConstant: 40.0),

			exampleConstraint,
			constrainedView.topAnchor.constraint(greaterThanOrEqualTo: scrollView.topAnchor),
			constrainedView.leadingAnchor.constraint(equalTo: anchorView.leadingAnchor, constant: 0.0),
			constrainedView.trailingAnchor.constraint(equalTo: anchorView.trailingAnchor, constant: 0.0),
			constrainedView.heightAnchor.constraint(equalToConstant: 120.0),
		])
		
		scrollView.delegate = self
	}
	
	func scrollViewDidScroll(_ scrollView: UIScrollView) {
		let up = scrollView.contentOffset.y
		print("up \(up)")
		exampleConstraint.constant = -up
	}
	
}