Widget preview View Controller for automated screenshots

WidgetPreviewController.swift

//
//  WidgetPreviewController.swift
//
//  Created by Emilio Peláez on 12/09/2020.
//

import UIKit
import SwiftUI

class WidgetPreviewController: UIViewController {
	
	var backgroundImage: UIImage? {
		get { imageView.image }
		set { imageView.image = newValue }
	}
	
	private let imageView = UIImageView()
	private let stackView = UIStackView()
	
	private var topConstraint: NSLayoutConstraint!
	private var leadingConstraint: NSLayoutConstraint!
	private var trailingConstraint: NSLayoutConstraint!
	
	override func viewDidLoad() {
		super.viewDidLoad()
		
		view.addSubview(imageView)
		view.addSubview(stackView)
		
		imageView.contentMode = .scaleAspectFill
		imageView.translatesAutoresizingMaskIntoConstraints = false
		view.topAnchor.constraint(equalTo: imageView.topAnchor).isActive = true
		view.leadingAnchor.constraint(equalTo: imageView.leadingAnchor).isActive = true
		view.trailingAnchor.constraint(equalTo: imageView.trailingAnchor).isActive = true
		view.bottomAnchor.constraint(equalTo: imageView.bottomAnchor).isActive = true
		
		stackView.axis = .vertical
		stackView.translatesAutoresizingMaskIntoConstraints = false
		topConstraint = stackView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor)
		leadingConstraint = stackView.leadingAnchor.constraint(equalTo: view.leadingAnchor)
		trailingConstraint = view.trailingAnchor.constraint(equalTo: stackView.trailingAnchor)
		
		[topConstraint, leadingConstraint, trailingConstraint]
			.forEach { $0?.isActive = true }
	}
	
	var spacing: CGFloat {
		floor(view.bounds.width * 0.06)
	}
	var widgetHeight: CGFloat {
		(view.bounds.width - 3 * spacing) / 2
	}
		
	override func viewDidLayoutSubviews() {
		super.viewDidLayoutSubviews()
		
		topConstraint.constant = 25
		leadingConstraint.constant = spacing
		trailingConstraint.constant = spacing
		
		stackView.spacing = spacing
	}
	
	enum Side {
		case left
		case right
	}
	
	func addSmallWidget<V: View>(view: V, side: Side) {
		addSmallWidgets(left: view, showLeft: side == .left, right: view, showRight: side == .right)
	}
	
	func addSmallWidgets<V1: View, V2: View>(left: V1, right: V2) {
		addSmallWidgets(left: left, showLeft: true, right: right, showRight: true)
	}
	
	func addSmallWidgets<V1: View, V2: View>(left: V1, showLeft: Bool, right: V2, showRight: Bool) {
		let stackView = UIStackView()
		stackView.axis = .horizontal
		stackView.spacing = spacing
		stackView.alignment = .fill
		stackView.distribution = .fillEqually
		stackView.heightAnchor.constraint(equalToConstant: widgetHeight).isActive = true
		
		let containerLeft = WidgetContainer(view: left)
		containerLeft.alpha = showLeft ? 1 : 0
		stackView.addArrangedSubview(containerLeft)
		
		let containerRight = WidgetContainer(view: right)
		containerRight.alpha = showRight ? 1 : 0
		stackView.addArrangedSubview(containerRight)
		
		self.stackView.addArrangedSubview(stackView)
	}
	
	func addMediumWidget<V: View>(view: V) {
		let container = WidgetContainer(view: view)
		container.heightAnchor.constraint(equalToConstant: widgetHeight).isActive = true
		stackView.addArrangedSubview(container)
	}
	
	func addLargeWidget<V: View>(view: V) {
		let container = WidgetContainer(view: view)
		container.widthAnchor.constraint(equalTo: container.heightAnchor).isActive = true
		stackView.addArrangedSubview(container)
	}
	
	override var preferredStatusBarStyle: UIStatusBarStyle { .lightContent }
	
	class WidgetContainer<V: View>: UIView {
		
		let hostingController: UIHostingController<V>
		
		init(view: V) {
			hostingController = UIHostingController(rootView: view)
			
			super.init(frame: .zero)
			
			translatesAutoresizingMaskIntoConstraints = false
			
			backgroundColor = .white
			layer.cornerRadius = 20
			layer.cornerCurve = .continuous
			layer.masksToBounds = true
			
			addSubview(hostingController.view)
		}
		
		required init?(coder: NSCoder) { fatalError() }
		
		override func layoutSubviews() {
			super.layoutSubviews()
			
			hostingController.view.frame = bounds
		}
	}
	
}