uicollectionview pinterest layout swift

pinterestlaout.swift

//
//  PinterestLayout.swift
//  Papr
//
//  Created by Joan Disho on 26.05.18.
//  Copyright © 2018 Joan Disho. All rights reserved.
//
import RxSwift
import RxCocoa

@objc
protocol PinterestLayoutDelegate: class {
    func collectionView(_ collectionView: UICollectionView, sizeForPhotoAtIndexPath indexPath: IndexPath) -> CGSize
}

class PinterestLayout: UICollectionViewLayout {

    // MARK: Delegate
    weak var delegate: PinterestLayoutDelegate?

    // MARK: Fileprivates
    fileprivate let cellPadding: CGFloat = 1 / UIScreen.main.scale
    fileprivate var numberOfColumns: Int = 0
    fileprivate var contentHeight: CGFloat = 0
    fileprivate var contentWidth: CGFloat {
        guard let collectionView = collectionView else { return 0 }
        let insets = collectionView.contentInset
        return collectionView.bounds.width - (insets.left + insets.right)
    }
    fileprivate var cache = [UICollectionViewLayoutAttributes]()

    init(numberOfColumns: Int) {
        self.numberOfColumns = numberOfColumns
        super.init()
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    // MARK: Overrides
    override var collectionViewContentSize: CGSize {
        return CGSize(width: contentWidth, height: contentHeight)
    }
    
    override func prepare() {
        guard cache.isEmpty,
            let collectionView = collectionView,
            collectionView.numberOfSections > 0 else { return }

        let columnWidth = contentWidth / CGFloat(numberOfColumns)
        var xOffset = [CGFloat]()

        for column in 0..<numberOfColumns {
            xOffset.append(CGFloat(column) * columnWidth)
        }

        var column = 0
        var yOffset = [CGFloat](repeating: 0, count: numberOfColumns)
        
        for item in 0..<collectionView.numberOfItems(inSection: 0) {
            let indexPath = IndexPath(item: item, section: 0)
            
            let size = delegate?.collectionView(collectionView, sizeForPhotoAtIndexPath: indexPath) ?? CGSize(width: 100, height: 100)
            let cellContentHeight = size.height * columnWidth / size.width
            let height = cellPadding + cellContentHeight
            let frame = CGRect(x: xOffset[column], y: yOffset[column], width: columnWidth, height: height)
            let insetFrame = frame.insetBy(dx: cellPadding, dy: cellPadding)

            let attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
            attributes.frame = insetFrame
            cache.append(attributes)

            contentHeight = max(contentHeight, frame.maxY)
            yOffset[column] = yOffset[column] + height

            column = column < (numberOfColumns - 1) ? (column + 1) : 0
        }
    }

    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        var visibleLayoutAttributes = [UICollectionViewLayoutAttributes]()
        for attributes in cache where attributes.frame.intersects(rect) {
            visibleLayoutAttributes.append(attributes)
        }
        return visibleLayoutAttributes
    }

    override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        return cache[indexPath.row]
    }

    override func invalidateLayout() {
        cache.removeAll()
        super.invalidateLayout()
    }

    override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
        return true
    }
}

class RxPinterestLayoutDelegateProxy: DelegateProxy<PinterestLayout, PinterestLayoutDelegate>, PinterestLayoutDelegate, DelegateProxyType {

    weak private(set) var pinterestLayout: PinterestLayout?
    var sizes:[IndexPath: CGSize] = [:]

    init(pinterestLayout: PinterestLayout) {
        self.pinterestLayout = pinterestLayout
        super.init(parentObject: pinterestLayout, delegateProxy: RxPinterestLayoutDelegateProxy.self)
    }

    static func registerKnownImplementations() {
        self.register { RxPinterestLayoutDelegateProxy(pinterestLayout: $0) }
    }

    static func currentDelegate(for object: PinterestLayout) -> PinterestLayoutDelegate? {
        return object.delegate
    }

    static func setCurrentDelegate(_ delegate: PinterestLayoutDelegate?, to object: PinterestLayout) {
        object.delegate = delegate
    }

    func collectionView(_ collectionView: UICollectionView, sizeForPhotoAtIndexPath indexPath: IndexPath) -> CGSize {
        return sizes[indexPath] ?? CGSize(width: 100, height: 100)
    }
}

extension Reactive where Base: PinterestLayout {

    private var delegate: RxPinterestLayoutDelegateProxy {
        return RxPinterestLayoutDelegateProxy.proxy(for: base)
    }

    func updateSize(_ indexPath: IndexPath) -> Binder<CGSize> {
        return Binder(base) { base, size in
            self.delegate.sizes[indexPath] = size
            base.invalidateLayout()
        }
    }
}