Make spacing and section insets equal

UICollectionViewFlowLayout+EqualSpacing.swift

import UIKit

extension UICollectionViewFlowLayout {
    func equalizeSpacing(with minimumSpacing: CGFloat, aItemSize: CGSize? = nil, sectionInsetTop: CGFloat = 0, sectionInsetBottom: CGFloat = 0) {
        guard let collectionView = collectionView else { return }
        
        let totalWidth = collectionView.frame.width
        
        let itemSizeToUse = aItemSize ?? itemSize
        itemSize = itemSizeToUse
        
        func columnsFit(with numberOfColumns: Int) -> Bool {
            let cellsWidth = CGFloat(numberOfColumns) * itemSize.width
            let spacingWidth = CGFloat(numberOfColumns + 1) * minimumSpacing
            
            return (cellsWidth + spacingWidth) < totalWidth
        }
        
        var columns = 1
        
        while columnsFit(with: columns) {
            let newPossible = columns + 1
            if columnsFit(with: newPossible) {
                columns = newPossible
            }
            else {
                break
            }
        }
        
        let cellsWidth = CGFloat(columns) * itemSize.width
        let spacing = CGFloat(totalWidth - cellsWidth) / CGFloat(columns + 1)
        
        minimumInteritemSpacing = spacing
        sectionInset = UIEdgeInsets(top: 0, left: spacing, bottom: 0, right: spacing)
    }
}