DeduplicatingCollectionViewSelector.swift

import UIKit

/**
 Enables smooth collection view selection by de-duplicating calls to `selectItemAtIndexPath:animated:scrollPosition:`
 
 If `selectItemAtIndexPath:animated:scrollPosition:` is being driven off of something like `scrollViewDidScroll:`
 delegate calls, we’d likely be invoking the former needlessly, with the same index path. This can result in jerky 
 scrolling.
 
 This class will ensure that we ignore any calls to `selectItemAtIndexPath:animated:scrollPosition:` that are identical 
 to the preceding call.
 */
final class DeduplicatingCollectionViewSelector {
    // MARK: - Public
    
    /// Whether the collection view should actually be scrolled. Ignores calls to `selectItemAtIndexPath:animated:scrollPosition:` when `true`.
    var enabled: Bool = true

    // MARK: - Mutable state
    
    fileprivate var lastIndexPath: IndexPath?

    // MARK: - Input
    
    fileprivate let collectionView: UICollectionView
    
    // MARK: - Initialization
    
    init(collectionView: UICollectionView) {
        self.collectionView = collectionView
    }
    
    // MARK: - Public
    
    func selectItem(at indexPath: IndexPath, scrollPosition: UICollectionViewScrollPosition, animated: Bool) {
        guard enabled else { return }
        guard indexPath != lastIndexPath else { return }
        
        lastIndexPath = indexPath
        
        collectionView.selectItem(at: indexPath, animated: animated, scrollPosition: scrollPosition)
    }
}