Fix observe order

[Luna712]

Fixes #2746
Closes #2750

[fire-light42]

This still relies on unproven semantics. I feel like we need to refactor this part rather than patching it. I will take a closer look on how we can solve this correctly.

[Luna712]

Fair enough and yeah it does. I just thought a better fix then relying on .value, as simply changing observe order and couldn't reproduce the issue anymore but yeah it is still just a patch fix. I didnt really like either but this one just felt "safer" and more reliable then the other way.

[fire-light42]

Fair enough and yeah it does. I just thought a better fix then relying on .value, as simply changing observe order and couldn't reproduce the issue anymore but yeah it is still just a patch fix. I didnt really like either but this one just felt "safer" and more reliable then the other way.

I will possibly make a pull request tomorrow, but the core idea is to have some immutable state to store all data needed to display the video. This state can then be efficiently modified using a persistent data type, and avoid concurrency issues by having it copy the data structure. We can then have a single source of truth for the entire player that exists within the viewmodel and can be exposed with e.g. ConsistentLiveData for both observe and .value without any issues.

typealias VideoLink = Pair<ExtractorLink?, ExtractorUri?>

/** Immutable state of all current links relevant to displaying the video */
data class VideoState(
    val subtitles: PersistentSet<SubtitleData>,
    val links: PersistentSet<VideoLink>,
    val stamps: PersistentSet<VideoSkipStamp>
) {
    /** This acts as a local cache for sorted links that are not copied over by the copy constructor */
    private val sortedLinks: ConcurrentHashMap<Int, List<VideoLink>> = ConcurrentHashMap()

    fun sortLinks(qualityProfile: Int) : List<VideoLink> {
        return sortedLinks[qualityProfile] ?: links.sortedBy { link ->
            // negative because we want to sort highest quality first
            -getLinkPriority(qualityProfile, link.first)
        }.also { value -> sortedLinks[qualityProfile] = value }
    }

    fun add(item: SubtitleData): VideoState = copy(subtitles = subtitles.add(item))
    fun add(item: VideoLink): VideoState = copy(links = links.add(item))
    fun add(item: VideoSkipStamp): VideoState = copy(stamps = stamps.add(item))
    fun add(items: Collection<SubtitleData>): VideoState = copy(subtitles = subtitles.addAll(items))
    fun add(items: Collection<VideoLink>): VideoState = copy(links = links.addAll(items))
    fun add(items: Collection<VideoSkipStamp>): VideoState = copy(stamps = stamps.addAll(items))
}