class MyCell: UICollectionViewCell {
    static let reuseIdentifier: String = "c"
}

class FullScreenCollVC: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout {

    var pageCollectionView: UICollectionView!

    let colors: [UIColor] = [
        .cyan, .yellow, .systemGreen, .systemBlue,
    ]

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .red
        setupPageCollectionView()
    }
    private func setupPageCollectionView() {

        let flowLayout: UICollectionViewFlowLayout = UICollectionViewFlowLayout()
        flowLayout.scrollDirection = .horizontal
        flowLayout.minimumInteritemSpacing = 0
        flowLayout.minimumLineSpacing = 0
        flowLayout.sectionInset = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)

        self.view.backgroundColor = .red

        pageCollectionView = UICollectionView(frame: .zero, collectionViewLayout: flowLayout)
        pageCollectionView.register(MyCell.self, forCellWithReuseIdentifier: MyCell.reuseIdentifier)
        pageCollectionView.delegate = self
        pageCollectionView.dataSource = self
        pageCollectionView.decelerationRate = .fast
        pageCollectionView.translatesAutoresizingMaskIntoConstraints = false

        pageCollectionView.backgroundColor = .blue
        self.view.addSubview(pageCollectionView)
        NSLayoutConstraint.activate([
            pageCollectionView.topAnchor.constraint(equalTo: self.view.topAnchor),
            pageCollectionView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor),
            pageCollectionView.trailingAnchor.constraint(equalTo: self.view.trailingAnchor),
            pageCollectionView.bottomAnchor.constraint(equalTo: self.view.bottomAnchor)
        ])

    }
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        print(indexPath.item, collectionView.bounds.size)
        return collectionView.bounds.size
    }
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 5
    }
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let c = collectionView.dequeueReusableCell(withReuseIdentifier: MyCell.reuseIdentifier, for: indexPath) as! MyCell
        c.contentView.backgroundColor = colors[indexPath.item % colors.count]
        return c
    }

}