import UIKit

class MarkSheetCollectionViewLayout: UICollectionViewLayout {
    //MARK: #1
    private enum Consts {
        static let rowHeaderWidth: CGFloat = 100
        static let oneRowHeight: CGFloat = 50
        static let columnHeaderHeight: CGFloat = 40
    }
    //MARK: #2
    private var numberOfColumns: Int {
        return collectionView!.numberOfItems(inSection: 0)
    }
    private var numberOfRows: Int {
        return collectionView!.numberOfSections
    }
    //MARK: #3
    private var columnWidth: CGFloat {
        let contentWidth = collectionViewContentSize.width - Consts.rowHeaderWidth
        return (contentWidth / CGFloat(numberOfColumns))
    }
    //MARK: #4
    override var collectionViewContentSize: CGSize {
        let contentHght = Consts.columnHeaderHeight + Consts.oneRowHeight * CGFloat(numberOfRows)
        return CGSize(width: collectionView?.bounds.width ?? 0, height: contentHght)
    }
    //MARK: #5
    override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
        return collectionView?.bounds.width != newBounds.width
    }
}