Example of a fancy zip chain

rxjava2.kt

override fun getDocumentAndAudiobook(docId: Int): Single<AudioData.LoaderResult> {
        val licenseRequest = audioApi.getLicense(docId).toObservable()
        val documentRequest = documentLoaderObservable(docId)
        val requests = mutableListOf(licenseRequest, documentRequest)
        return Observable.zip(requests,
                Function<Array<Any>, CombinedResult> {
                    return@Function resolve(it)
                })
                .flatMap(Function<CombinedResult, Observable<Pair<ScribdDocument, FindawayApi.PlayListResponse>>> {
                    val playlistRequest = audioApi.getPlaylist(
                            faeDocId = it.document.audiobook.externalId.toInt(),
                            licenseId = it.license,
                            sessionKey = it.sessionKey).toObservable()

                    return@Function Observable.zip(
                            Observable.just(it.document),
                            playlistRequest,
                            BiFunction<ScribdDocument, FindawayApi.PlayListResponse, Pair<ScribdDocument, FindawayApi.PlayListResponse>> { document, playlist ->
                                return@BiFunction Pair(document, playlist)
                            })
                })
                .flatMap(Function<Pair<ScribdDocument, FindawayApi.PlayListResponse>, Observable<AudioData.LoaderResult>> {
                    val audiobook = buildAudiobook(it.first, it.second)
                    return@Function Observable.just(AudioData.LoaderResult(it.first, audiobook))
                }).firstOrError()
    }