TrainDepartureService.swift

class TrainDepartureService {

  func departureTimes(forLine: TrainLine, departingFrom: TrainStation) -> Observable<Date> {
    return Observable<TimeInterval>.timer(0, period: 60, scheduler: scheduler)
      .flatMapLatest { _ -> Observable<Date> in
        network.departureTime(forLine: forLine, departingFrom: departingFrom)
      }
  }

  private let scheduler: SchedulerType
  private let network: TrainNetworkHandler
  init(
    scheduler: SchedulerType,
    network: TrainNetworkHandler
  ) {
    self.scheduler = scheduler
    self.network = network
  }
}