class ViewController: UIViewController {

    @IBOutlet private weak var collectionView: UICollectionView! {
        didSet {
            let layout = WaterfallLayout()
            layout.delegate = self
            layout.sectionInset = UIEdgeInsets(top: 16, left: 16, bottom: 16, right: 16)
            layout.minimumLineSpacing = 8.0
            layout.minimumInteritemSpacing = 8.0
            layout.headerHeight = 50.0
            collectionView.collectionViewLayout = layout
            collectionView.register(...)
            collectionView.dataSource = self
            collectionView.delegate = self
        }
    }
}

extension ViewController: UICollectionDataSource {
    ...
}

extension ViewController: WaterfallLayoutDelegate {
    func collectionViewLayout(for section: Int) -> WaterfallLayout.Layout {
        switch section {
        case 0: return .flow(column: 1) // single column flow layout
        case 1: return .waterfall(column: 3) // three waterfall layout
        default: return .flow(column: 2)
        }
    }

    func collectionView(_ collectionView: UICollectionView, layout: WaterfallLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return CGSize(...)
    }    
}

public var minimumLineSpacing: CGFloat { get set }

public var minimumInteritemSpacing: CGFloat { get set }

public var sectionInset: UIEdgeInsets  { get set }

public var headerHeight: CGFloat  { get set }

public var headerInset: UIEdgeInsets { get set }

public var footerHeight: CGFloat { get set }

public var footerInset: UIEdgeInsets { get set }

public var estimatedItemSize: CGSize { get set }

public protocol WaterfallLayoutDelegate: class {
    // MARK: - Required
    func collectionViewLayout(for section: Int) -> WaterfallLayout.Layout
    func collectionView(_ collectionView: UICollectionView, layout: WaterfallLayout, sizeForItemAt indexPath: IndexPath) -> CGSize

    // MARK: - Optional
    func collectionView(_ collectionView: UICollectionView, layout: WaterfallLayout, minimumInteritemSpacingFor section: Int) -> CGFloat?
    func collectionView(_ collectionView: UICollectionView, layout: WaterfallLayout, minimumLineSpacingFor section: Int) -> CGFloat?
    func collectionView(_ collectionView: UICollectionView, layout: WaterfallLayout, sectionInsetFor section: Int) -> UIEdgeInsets?
    func collectionView(_ collectionView: UICollectionView, layout: WaterfallLayout, headerHeightFor section: Int) -> CGFloat?
    func collectionView(_ collectionView: UICollectionView, layout: WaterfallLayout, headerInsetFor section: Int) -> UIEdgeInsets?
    func collectionView(_ collectionView: UICollectionView, layout: WaterfallLayout, footerHeightFor section: Int) -> CGFloat?
    func collectionView(_ collectionView: UICollectionView, layout: WaterfallLayout, footerInsetFor section: Int) -> UIEdgeInsets?
    func collectionView(_ collectionView: UICollectionView, layout: WaterfallLayout, estimatedSizeForItemAt indexPath: IndexPath) -> CGSize?
}