DataSourcesWithouRxSwift

import UIKit
import DataSources

protocol Model {
    var title: String { get }
}

struct ModelM : Model, Diffable {
    
    var diffIdentifier: AnyHashable {
        return AnyHashable(identity)
    }
    
    let identity: String
    let title: String
}

final class Cell : UICollectionViewCell{
    
    let label = UILabel()
    private let paddingView = UIView()
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        
        contentView.addSubview(paddingView)
        contentView.addSubview(label)
        
        label.textAlignment = .center
        label.font = UIFont.systemFont(ofSize: 20)
        
        paddingView.backgroundColor = UIColor(white: 0.95, alpha: 1)
        paddingView.layer.cornerRadius = 4
        paddingView.layer.shouldRasterize = true
        paddingView.layer.rasterizationScale = UIScreen.main.scale
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}


class ViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout  {
    let collectionView = UICollectionView()

    private lazy var sectionDataController = SectionDataController<ModelM, CollectionViewAdapter>(
        adapter: CollectionViewAdapter(collectionView: self.collectionView),
        isEqual: { $0.identity == $1.identity } // If Model has Equatable, you can omit this closure.
    )

    var models: [ModelM] = [] {
        didSet {
            sectionDataController.update(items: models, updateMode: .partial(animated: true), completion: {
                // Completed update
            })
        }
    }
    
    private lazy var dataSource = CollectionViewDataSource(sectionDataSource: sectionDataController)
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        collectionView.delegate = self
        collectionView.dataSource = self
        
        self.view.addSubview(collectionView)
        collectionView.frame = self.view.bounds
        collectionView.autoresizingMask = [.flexibleWidth, .flexibleHeight]

        dataSource.cellFactory = { _, collectionView, indexPath, model in
            let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! Cell
            cell.label.text = model.title
            return cell
        }
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return dataSource.numberOfSections(in:)
    }
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return dataSource.numberOfItems(in: section)
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! Cell
        let m = dataSource.item(at: indexPath, in: section0)
        cell.label.text = m.title
        return cell
    }
    
    func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
        if kind == UICollectionElementKindSectionHeader {
            let view = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: "Header", for: indexPath) as! Header
            view.label.text = "Section " + indexPath.section.description
            return view
        }
        fatalError()
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, referenceSizeForHeaderInSection section: Int) -> CGSize {
        
        return CGSize(width: collectionView.bounds.width, height: 50)
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        
        return CGSize(width: collectionView.bounds.width / 6, height: 50)
    }
}