TableViewWithCollection.swift

class TableCollectionViewController: UIViewController {
    let collectionView : UICollectionView = {
        let layout = UICollectionViewCompositionalLayout.list(using: UICollectionLayoutListConfiguration(appearance: .plain))
        let collectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)
        collectionView.translatesAutoresizingMaskIntoConstraints = false
        return collectionView
    }()
    lazy var collectionDataSource = CollectionDataSource(collectionView: collectionView)
    
    override func viewDidLoad() {
        super.viewDidLoad()
        title = "TableCollection"
        setup()
    }
    
    func setup() {
        view.addSubview(collectionView)
        NSLayoutConstraint.activate([
            collectionView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
            collectionView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            collectionView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            collectionView.bottomAnchor.constraint(equalTo: view.bottomAnchor)
        ])
        let button = UIBarButtonItem(image: .add, style: .plain, target: self, action: #selector(addItem))
        navigationItem.rightBarButtonItem = button
        collectionDataSource.snapshotData(items: (1...2).map{ Item(text: "Demo \($0)") })
    }
    
    @objc
    func addItem() {
        let item = Item(text: "collection item")
        collectionDataSource.snapshotData(items: [item])
    }
}

class ItemCollectionCell: UICollectionViewCell {
    override var reuseIdentifier: String? {
        "ItemCollectionCell"
    }
}

class CollectionDataSource {
    typealias DataSource = UICollectionViewDiffableDataSource<Section, Item>
    typealias Diffable = NSDiffableDataSourceSnapshot<Section, Item>
    
    private let collectionView: UICollectionView
    
    let itemCellRegistration = UICollectionView.CellRegistration<ItemCollectionCell, Item> { cell, indexPath, item in
        var config = UIListContentConfiguration.subtitleCell()
        config.text = item.text
        cell.contentConfiguration = config
    }
    lazy var dataSource = DataSource(collectionView: collectionView) { [weak self] collectionView, indexPath, itemIdentifier in
        guard let self else { return UICollectionViewCell() }
        let cell = collectionView.dequeueConfiguredReusableCell(using: itemCellRegistration, for: indexPath, item: itemIdentifier)
        return cell
    }
    var diffable = Diffable()
    
    init(collectionView: UICollectionView) {
        self.collectionView = collectionView
        setup()
    }
    
    func setup() {
        diffable.appendSections([.main])
    }
    
    func snapshotData(items: [Item]) {
        diffable.appendItems(items, toSection: .main)
        dataSource.apply(diffable)
    }
}

struct Item: Hashable, Identifiable {
    let id: UUID = UUID()
    let text: String
}

enum Section {
    case main
}