CollectionViewListRenderer.swift

class UICollectionViewListRenderer: ListRenderer {
    private var ignoringUpdates: Bool = false

    weak var collectionView: UICollectionView?
    init(collectionView: UICollectionView?) {
        self.collectionView = collectionView
    }
    func reloadData() {
        collectionView?.reloadData()
    }
    func reloadSections(_ sections: [Int]) {
        guard !ignoringUpdates else { return }
        modify { $0.reloadSections(IndexSet(sections)) }

    }
    func deleteSections(_ sections: [Int]) {
        modify { $0.deleteSections(IndexSet(sections)) }
    }
    func insertSections(_ sections: [Int]) {
        modify { $0.insertSections(IndexSet(sections)) }
    }
    func reloadItems(at indexPaths: [IndexPath]) {
        guard !ignoringUpdates else { return }
        modify { $0.reloadItems(at: indexPaths) }
    }
    func insertItems(at indexPaths: [IndexPath]) {
        modify { $0.insertItems(at: indexPaths) }
    }
    func deleteItems(at indexPaths: [IndexPath]) {
        modify { $0.deleteItems(at: indexPaths) }
    }


    /// Runs modification update on collection view if collection view is visible
    /// If collection view is not present on window= it ignores update and just calls reloadData(
    /// - Parameter action: mofidictaion action
    private func modify(_ action: (UICollectionView) -> ()) {
        guard let collectionView = collectionView, collectionView.window != nil else { reloadData(); return }
        action(collectionView)
    }


    func withIgnoringUpdates(block: () -> ()) {
        ignoringUpdates = true
        block()
        ignoringUpdates = false
    }

}