PanelHandleViewModel.kt

class PanelHandleViewModel {
    // Gives us player status information
    private lateinit var player: Player
    // Multicasts emissions of what's currently selected for playback.
    private lateinit var provider: PodcastProvider

    fun handleMetaState(): Observable<PlayerHandleMetaState> {
        return provider.currentlyPlaying()
                .map { podcast ->
                      //Convert your model into information relevant to the View.
                    PlayerHandleMetaState(
                            podcast.title,
                            podcast.author,
                            podcast.albumArtUrl,
                            podcast.accentColor)
                }

    }

    fun handleIconState(): Observable<PlayerHandleIconState> {
        val icon = player.state()
                .map { state -> if (state == Player.State.PLAYING) R.drawable.ic_pause else R.drawable.ic_play }

        val color = provider.currentlyPlaying()
                .map { podcast -> podcast.accentColor }

        //Combine both data streams, since a change from either source needs to result into a UI update.
        return Observable.combineLatest(icon, color, BiFunction { i, c -> PlayerHandleIconState(i, c) })
    }


    fun handleProgress(): Observable<PlayerHandleProgressState> {
        val timeElapsed = player.timeElapsed()

        val trackLength = provider.currentlyPlaying().map { podcast -> podcast.length }

        //Make a point to keep any sort of formatting, control flow, or calculation out of the View, since it's easier to test.
        return Observable.combineLatest(timeElapsed, trackLength,
                BiFunction { elapsed, duration -> PlayerHandleProgressState(elapsed.times(100).div(duration)) })
    }
}