Two observables as Flat map

twoObservablesFlatMap.kt

/**
 * Returns an observable from a function that decrypts stored user data
 */
fun currentUserObservable(): Observable<UserViewModel> {
    return Observable.create(ObservableOnSubscribe<UserViewModel> { subscriber ->
        val user = currentUser()
        if (user != null)
            subscriber.onNext(user)
        else
            subscriber.onError(Throwable("User is null"))
        subscriber.onComplete()
    }).subscribeOn(Schedulers.io())
      .observeOn(AndroidSchedulers.mainThread())
}

/**
 * Returns an onservable from a function that decrypts stored auth token
 */
fun currentTokenObservable(): Observable<String> {
    return Observable.create(ObservableOnSubscribe<String> { subscriber ->
        val authToken = currentAuthToken()
        if (!authToken.isNullOrEmpty())
            subscriber.onNext(authToken!!)
        else
            subscriber.onError(Throwable("Auth Token is null"))
        subscriber.onComplete()
    }).subscribeOn(Schedulers.io())
      .observeOn(AndroidSchedulers.mainThread())
}


/**
 * Calls the getAmoun Service to obtain the info from the user
 * @return Observable<AmountResponseViewModel>
 */
internal fun getAmountService(): Observable<AmountResponseViewModel> {
    return amountLocalStorage.currentAuthTokenObservable().flatMap { 
        authToken: String -> userLocalStorage.currentUserObservable().flatMap {
        user: UserViewModel -> retrofit.create(AmountService::class.java)
                .amount(authToken, user.id, user.secondaryId)
    } }
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
}