Spek with Subjects - Presenter

DistancesPresenter.kt

class DistancesPresenter @Inject constructor(private val roundInteractor: RoundInteractor) {
    
    private val subscriptions by lazy { CompositeSubscription() }
    
    private lateinit var view: View
    
    fun attachView(view: View) {
        this.view = view
    }
    
    fun start() {
        subscriptions.add(
                Observable.combineLatest(
                        roundInteractor.changeHoleEvents(),
                        roundInteractor.distanceUnitEvents(),
                        roundInteractor.distancesEvents(),
                        { hole: Hole, distanceUnit: DistanceUnit, distances: List<RoundDistances> ->
                            val isMetricDistanceUnit = distanceUnit == DistanceUnit.METRIC
                            val distancesToGreen = distances[hole.sequence - 1].let { 
                                holeDistances -> if (isMetricDistanceUnit) {
                                    holeDistances
                                } else {
                                    toImperial(holeDistances)
                                }
                            }
                         
                            Pair(distancesToGreen, isMetricDistanceUnit)
                        })
                        .subscribeOn(Schedulers.io())
                        .observeOn(AndroidSchedulers.mainThread())
                        .subscribe(object : DefaultSubscriber<Pair<RoundDistances, Boolean>>() {
                            override fun onNext(distances: Pair<RoundDistances, Boolean>) {
                                view.displayDistancesToGreen(
                                        distances.first.greenBackDistance.toString(),
                                        distances.first.greenCenterDistance.toString(),
                                        distances.first.greenFrontDistance.toString())
                                view.displayDistanceUnit(distances.second)
                            }

                            override fun onError(e: Throwable) {
                                // handle error
                            }
                        })
        )
    }
       
    fun stop() {
        subscriptions.clear()
    }
    
    private fun toImperial(distances: RoundDistances) = 
        RoundDistances(toYards(distance.back), toYards(distances.center), toYards(distances.front))
    
    private fun toYards(meters: Int) = Math.round(meters * 1.0936)
    
    interface View {
        fun displayDistancesToGreen(distanceToGreenBack: String, distanceToGreenCenter: String, distanceToGreenFront: String)
        fun displayDistanceUnit(isMetricDistanceUnit: Boolean)
    }
}