Paging a UICollectionView when each cell is smaller than the width of the collection

Example.swift

// Set the inset so that the first and last cells can appear in the middle of the UICollectionView
override func layoutSubviews() {
    super.layoutSubviews()
    contentInset = UIEdgeInsets(top: 0, left: frame.width / 2.0 - layout.itemSize.width / 2.0, bottom: 0, right: 0)
}

private func currentCentredCell() -> UICollectionViewCell? {
    return visibleCells.reduce(visibleCells.first) { (nearestCell, nextCell) -> UICollectionViewCell? in
        
        // We need the paging to set the scrollView to show a ticket centered.
        // Compare the distance between the midpoint of each cell (translated to the collectionView's coordinate space)
        // with that of the cell after it. Return the cell with the nearest distance, and repeat for all visible cells
            
        guard let cellA = nearestCell else { return nextCell }
        
        let rectA = convert(cellA.frame, from: cellA.superview)
        let rectB = convert(nextCell.frame, from: nextCell.superview)
            
        let collectionViewMid = bounds.midX
            
        let dxA = abs(rectA.midX - collectionViewMid)
        let dxB = abs(rectB.midX - collectionViewMid)
        if dxA < dxB {
            return cellA
        } else {
            return nextCell
        }
    }
}

private func xOffsetFor(cell: UICollectionViewCell) -> CGFloat {

    let rect = convert(cell.frame, from: cell.superview)
    return rect.origin.x
}

func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
    
    guard let nearestCell = currentCentredCell() else { return }
    guard let idx = indexPath(for: nearestCell)?.row else { return }
    
    // Snap to the correct page according to the phyisics of the scroll
    
    if velocity.x > 0 {
        
        if idx + 1 < numberOfItems(inSection: 0) {
            if let att = layoutAttributesForItem(at: .init(row: idx + 1, section: 0)) {
                targetContentOffset.pointee.x = att.frame.origin.x - frame.width / 2.0 + att.frame.width / 2.0
                return
            }
        }
        
    } else if velocity.x < 0 {
        
        if idx - 1 >= 0 {
            if let att = layoutAttributesForItem(at: .init(row: idx - 1, section: 0)) {
                targetContentOffset.pointee.x = att.frame.origin.x - frame.width / 2.0 - att.frame.width / 2.0
                return
            }
        }
    }
    
    // default
    let att = layoutAttributesForItem(at: .init(row: idx, section: 0))!
    targetContentOffset.pointee.x = xOffsetFor(cell: nearestCell) - frame.width / 2.0 - att.frame.width / 2.0
}