gistfile1.txt

//
//  OneLineForEachSectionLayout.swift
//
//  Created by Philipp Kinschel on 28/11/2016.
//
//
//
// very basic solution to layout one section in one line without linebreaks
// TODO: find name for the class
//

import UIKit

class OneLineForEachSectionLayout: UICollectionViewLayout {
    
    var itemSize = CGSize(width: 50, height: 50)
    var minimumInteritemSpacing: CGFloat = 10
    var minimumLineSpacing: CGFloat = 10
    
    private var cachedContentSize: CGSize = .zero
    private var cachedLayoutAttributes = [IndexPath: UICollectionViewLayoutAttributes]()
    
    override var collectionViewContentSize: CGSize {
        return self.cachedContentSize
    }
    
    override func prepare() {
        guard let collectionView = collectionView else { return }
        
        cachedContentSize = contentSize()
        
        cachedLayoutAttributes = [IndexPath: UICollectionViewLayoutAttributes]()
        for section in 0..<collectionView.numberOfSections {
            for item in 0..<collectionView.numberOfItems(inSection: section) {
                let indexPath = IndexPath(item: item, section: section)
                
                if let layoutAttributes = layoutAttributesForItem(at: indexPath) {
                    cachedLayoutAttributes[indexPath] = layoutAttributes
                }
            }
        }
    }
    
    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        return self.cachedLayoutAttributes.filter { (indexPath, layoutAttributes) -> Bool in
            return layoutAttributes.frame.intersects(rect)
            }.map({ (indexPath, layoutAttributes) -> UICollectionViewLayoutAttributes in
                return layoutAttributes
            })
    }
    
    override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        let layoutAttributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
        layoutAttributes.frame = CGRect(origin: originForItem(at: indexPath), size: itemSize)
        
        return layoutAttributes
    }
    
    private func originForItem(at indexPath: IndexPath) -> CGPoint {
        return CGPoint(x: horizontalOffsetForItem(at: indexPath), y: verticalOffsetForItem(at: indexPath))
    }
    
    private func horizontalOffsetForItem(at indexPath: IndexPath) -> Int {
        return indexPath.row * Int(itemSize.width + minimumInteritemSpacing)
    }
    
    private func verticalOffsetForItem(at indexPath: IndexPath) -> Int {
        return indexPath.section * Int(itemSize.height + minimumLineSpacing)
    }
    
    private func contentSize() -> CGSize {
        guard let collectionView = collectionView else { return .zero }
        
        let rows = maxNumberOfRows()
        
        return CGSize(width: rows * Int(itemSize.width + minimumInteritemSpacing),
                      height: collectionView.numberOfSections * Int(itemSize.height + minimumLineSpacing))
    }
    
    /// iterates through sections to determine largest amount of items per section
    private func maxNumberOfRows() -> Int {
        guard let collectionView = collectionView else { return 0 }
        
        var maxRows = 0
        for section in 0..<collectionView.numberOfSections {
            maxRows = max(maxRows, collectionView.numberOfItems(inSection: section))
        }
        
        return maxRows
    }
    
}