Custom UIScrollView paging

CollectionViewPaging.swift

func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
    let pageWidth = <#page width#>
    let collectionViewContentWidth = collectionView.contentSize.width

    if velocity.x == 0 {
        page = Int(floor((targetContentOffset.pointee.x - pageWidth / 2) / pageWidth) + 1.0)
    } else {
        page = velocity.x > 0 ? page + 1 : page - 1
        if page < 0 {
            page = 0
        }
        let pagesNumber = collectionViewContentWidth / pageWidth
        if page + 1 > Int(pagesNumber) {
            page = Int(ceil(pagesNumber) - 1.0)
        }
    }

    targetContentOffset.pointee = CGPoint(x: CGFloat(page) * pageWidth, y: targetContentOffset.pointee.y)
}