UIPageViewController with inifinite scrolling

ContainerViewController.swift

import UIKit

final class ContainerViewController: UIViewController {
    private let pageViewController: UIPageViewController = .init(transitionStyle: .scroll, navigationOrientation: .horizontal)
    private let childViews: [UIViewController] = {
        let vc0 = UIViewController()
        vc0.view.backgroundColor = .red
        let vc1 = UIViewController()
        vc1.view.backgroundColor = .red.withAlphaComponent(0.6)
        let vc2 = UIViewController()
        vc2.view.backgroundColor = .red.withAlphaComponent(0.4)
        let vc3 = UIViewController()
        vc3.view.backgroundColor = .red.withAlphaComponent(0.2)
        return [vc0, vc1, vc2, vc3]
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = .black

        if let pageView = pageViewController.view {
            view.addSubview(pageView)
            pageView.translatesAutoresizingMaskIntoConstraints = false
            NSLayoutConstraint.activate([
                pageView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
                pageView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
                pageView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
                pageView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor),
            ])
            pageView.backgroundColor = .white
        }

        pageViewController.dataSource = self
        pageViewController.setViewControllers([childViews[0]], direction: .forward, animated: false)
    }
}

extension ContainerViewController: UIPageViewControllerDataSource {
    func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
        guard let index = childViews.firstIndex(of: viewController) else { return nil }

        if index > 0 {
            return childViews[index - 1]
        } else {
            return childViews.last
        }
    }

    func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
        guard let index = childViews.firstIndex(of: viewController) else { return nil }

        if index < childViews.count - 1 {
            return childViews[index + 1]
        } else {
            return childViews.first
        }
    }
}