public protocol Diffable {
  associatedtype Identifier : Hashable
  var diffIdentifier: Identifier { get }
}

struct Model : Diffable {

  var diffIdentifier: String {
    return id
  }
  
  let id: String
}

let collectionView: UICollectionView

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

var models: [Model] = [] {
  didSet {
    sectionDataController.update(items: items, updateMode: .partial(animated: true), completion: {
      // Completed update
    })
  }
}

let dataSource = CollectionViewDataSource(sectionDataController: sectionDataController)

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

collectionView.dataSource = dataSource

let collectionView: UICollectionView
var models: [Model]

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

var models: [Model] = […] {
  didSet {
    sectionDataController.update(items: items, updateMode: .partial(animated: true), completion: {
      // Completed update
    })
  }
}

func numberOfSections(in collectionView: UICollectionView) -> Int {
  return 1
}

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
  return sectionDataController.numberOfItems()
}

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

  let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! Cell
  let m = sectionDataController.item(for: indexPath)
  cell.label.text = m.title
  return cell
}

let collectionView: UICollectionView
var models: [Model]

let dataController = DataController<CollectionViewAdapter>(adapter: CollectionViewAdapter(collectionView: self.collectionView))

let section0 = Section(ModelA.self, isEqual: { $0.id == $1.id })
let section1 = Section(ModelB.self, isEqual: { $0.id == $1.id })

dataController.add(section: section0) // will be 0 of section
dataController.add(section: section1) // will be 1 of section

var section0Models: [ModelA] = […] {
  didSet {
    dataController.update(
      in: section0,
      items: section0Models,
      updateMode: .partial(animated: true),
      completion: {
        
    })
  }
}

var section1Models: [ModelA] = […] {
  didSet {
    dataController.update(
      in: section1,
      items: section1Models,
      updateMode: .partial(animated: true),
      completion: {
        
    })
  }
}

func numberOfSections(in collectionView: UICollectionView) -> Int {
  return dataController.numberOfSections()
}

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
  return dataController.numberOfItems(in: section)
}

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

  return dataController.item(
    at: indexPath,    
    handlers: [
    .init(section: section0) { (m: ModelA) in
      let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! Cell
      cell.label.text = m.title
      return cell
    },
    .init(section: section1) { (m: ModelB) in
      let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! Cell
      cell.label.text = m.title
      return cell
      },
    ])

  /* Other way
  switch indexPath.section {
  case section0:
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! Cell
    let m = _dataController.item(at: indexPath, in: section0)
    cell.label.text = m.title
    return cell
  case section1:
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! Cell
    let m = _dataController.item(at: indexPath, in: section1)
    cell.label.text = m.title
    return cell
  default:
    fatalError()
  }
   */
}

import RxSwift
import DataControllers

extension SectionDataController : ReactiveCompatible {}

extension Reactive where Base : SectionDataControllerType {

  public func partialUpdate<
    T,
    Controller: ObservableType
    >
    (animated: Bool) -> (_ o: Source) -> Disposable where Source.E == [T], T == Base.ItemType {

    weak var t = base.asSectionDataController()

    return { source in

      source
        .observeOn(MainScheduler.instance)
        .concatMap { (newItems: [T]) -> Completable in
          Completable.create { o in
            guard let sectionDataController = t else {
              o(.completed)
              return Disposables.create()
            }
            sectionDataController.update(items: newItems, updateMode: .partial(animated: animated), completion: {
              o(.completed)
            })
            return Disposables.create()
          }
        }
        .subscribe()
    }
  }
}

let models: Variable<[Model]>
let sectionDataController = SectionDataController<Model, CollectionViewAdapter>

models
  .asDriver()
  .drive(sectionDataController.rx.partialUpdate(animated: true))