/*
Here is some sample code for a quick test of adding 48 labels (8 to each of 6 stack views).

The button at the top toggles between adding / removing the labels, so it can be run multiple times.

On an iPad Air (`ME991LL/A`), I get 0.03 seconds or less.
*/

class ViewController: UIViewController {
	
	let theBtn: UIButton = {
		let v = UIButton()
		v.translatesAutoresizingMaskIntoConstraints = false
		v.setTitle("Add Views", for: .normal)
		v.setContentHuggingPriority(.required, for: .vertical)
		v.backgroundColor = .red
		return v
	}()
	
	let promptLabel: UILabel = {
		let v = UILabel()
		v.translatesAutoresizingMaskIntoConstraints = false
		v.textAlignment = .center
		v.text = "Tap button to:"
		return v
	}()
	
	let statLabel: UILabel = {
		let v = UILabel()
		v.translatesAutoresizingMaskIntoConstraints = false
		v.backgroundColor = .cyan
		v.textAlignment = .center
		v.text = ""
		return v
	}()
	
	let topStackView: UIStackView = {
		let v = UIStackView()
		v.axis = .vertical
		v.distribution = .fillEqually
		v.spacing = 4
		v.translatesAutoresizingMaskIntoConstraints = false
		return v
	}()
	
	let hStackView: UIStackView = {
		let v = UIStackView()
		v.axis = .horizontal
		v.distribution = .fillEqually
		v.spacing = 8
		v.translatesAutoresizingMaskIntoConstraints = false
		return v
	}()

	var stackViews: [UIStackView] = [UIStackView]()
	
	var jCounter = 1

	override func viewDidLoad() {
		super.viewDidLoad()
		
		view.backgroundColor = .white
		
		for _ in 1...6 {
			let v = UIStackView()
			v.axis = .vertical
			v.distribution = .fillEqually
			v.spacing = 8
			v.translatesAutoresizingMaskIntoConstraints = false
			stackViews.append(v)
		}
		
		topStackView.addArrangedSubview(promptLabel)
		topStackView.addArrangedSubview(theBtn)
		topStackView.addArrangedSubview(statLabel)

		view.addSubview(topStackView)
		view.addSubview(hStackView)
		
		let g = view.safeAreaLayoutGuide
		
		NSLayoutConstraint.activate([
			
			topStackView.topAnchor.constraint(equalTo: g.topAnchor, constant: 20.0),
			topStackView.centerXAnchor.constraint(equalTo: g.centerXAnchor, constant: 0.0),
			topStackView.widthAnchor.constraint(equalToConstant: 300.0),
			
			hStackView.topAnchor.constraint(equalTo: topStackView.bottomAnchor, constant: 20.0),
			hStackView.bottomAnchor.constraint(equalTo: g.bottomAnchor, constant: -8.0),
			hStackView.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 8.0),
			hStackView.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: -8.0),

		])
		
		stackViews.forEach {
			hStackView.addArrangedSubview($0)
		}
		
		theBtn.addTarget(self, action: #selector(addViews(_:)), for: .touchUpInside)
		
	}
	
	func doAddViews() -> Void {

		let start = CFAbsoluteTimeGetCurrent()
		
		stackViews.forEach {
			sv in
			for _ in 1...8 {
				let v = UILabel()
				v.font = UIFont.systemFont(ofSize: 10.0, weight: .medium)
				v.backgroundColor = .yellow
				v.textAlignment = .center
				v.text = "\(jCounter)"
				sv.addArrangedSubview(v)
				jCounter += 1
			}
		}
		
		let end = CFAbsoluteTimeGetCurrent() - start
		
		statLabel.text = "Elapsed Time: \(end)"
		
	}
	
	@objc func addViews(_ sender: Any?) -> Void {

		if stackViews.first?.arrangedSubviews.count == 0 {

			doAddViews()
			
			theBtn.setTitle("Clear Views", for: .normal)

		} else {

			stackViews.forEach {
				sv in
				sv.arrangedSubviews.forEach {
					$0.removeFromSuperview()
				}
			}

			statLabel.text = ""

			theBtn.setTitle("Add Views", for: .normal)

		}
		
	}
	
}