class GlobalHook {

  static let shared = GlobalHook()

  var updateModel = PublishRelay<Model>()
}

protcol ViewModelProcotol {
  func hook()
}

struct repository {
  let store: ActionRelay<[Article]>

  func fetch() -> Observable<[Article]> {
   appService.request.map { $0.articles }.do(onNext: { [weak store] store?.accept($0) })
  }

  func more() -> Observable<[Article]> {
   appService.request.map { $0.articles }.do(onNext: { [weak store] in
    var items = store?.value ?? []
    items.append($0)
    store.accept(items)
   })
  }

  func itemsState() -> observable<[Article]> {
   return store.asObservable()
  }

}

class ViewModel: ViewModelProtocol {

  let refresh = PublishRelay<Void>()
  let more = PublishRelay<Void>()

  var output: Observable<ViewState>()

  private let converter = Converter()

  let worker = CustomWorker()

  init() {
   output = worker.itemsState().asObservable()
   refresh.flatMap { worker.fetch() }
   more.flatMap { worker.more() }

   hook()
  }

  func hook() {
    GlobalHook.shared.updateModel.bind(to: store).disposed(by: disposeBag)
  }
}

struct Worker {

  func loadModel() -> Observable<Model> { .... }
}

struct Converter {

  func viewState(_ model: Model) -> ViewState { ... }
}