grr.ts

const watchedEpisodesNow = (
  media: IMedia,
  season: ISeason,
  episode: IEpisode,
  watched: WatchedDocument | null,
  sawPrevius: boolean,
): [IEpisode[], SeasonWatch[]] => {
  if (!watched) {
    // CREATE NEW WATCHED
    if (sawPrevius) {
      const [episodes, seasons] = media.seasons.reduce<[IEpisode[], SeasonWatch[]]>(
        (acc, s) => {
          if (s.seasonNumber > season.seasonNumber) return acc;

          const watchedEpisodeNumbers = s.episodes.filter(
            (e) =>
              e.seasonNumber < season.seasonNumber ||
              (e.seasonNumber === season.seasonNumber && e.episodeNumber <= episode.episodeNumber),
          );

          acc[0].push(...watchedEpisodeNumbers);
          acc[1].push({
            seasonID: String(s._id.toString()),
            watchedEpisodeNumbers: watchedEpisodeNumbers.map((e) => e.episodeNumber),
          });

          return acc;
        },
        [[], []],
      );

      return [episodes, seasons];
    }

    return [
      [episode],
      [{ seasonID: String(season._id.toString()), watchedEpisodeNumbers: [episode.episodeNumber] }],
    ];
  }

  const watchedSeason = watched?.seasons.find((s) => compareID(s.seasonID, season._id));
  const episdodeAlreadySeen =
    watchedSeason?.watchedEpisodeNumbers?.includes(episode.episodeNumber) ?? false;

  if (episdodeAlreadySeen) {
    // REMOVE WATCHED EPISODE
    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
    watchedSeason!.watchedEpisodeNumbers = watchedSeason!.watchedEpisodeNumbers.filter(
      (e) => e !== episode.episodeNumber,
    );

    return [[episode], watched.seasons];
  }

  if (!sawPrevius) {
    // ADD WATCHED EPISODE
    if (watchedSeason) {
      watchedSeason.watchedEpisodeNumbers.push(episode.episodeNumber);
    } else {
      watched.seasons.push({
        seasonID: season._id,
        watchedEpisodeNumbers: [episode.episodeNumber],
      });
    }

    return [[episode], watched.seasons];
  }

  // ADD WATCHED EPISODE AND MODIFY PREVIOUS
  const watchedEpisodes: IEpisode[] = [];
  const watchedSeasons: SeasonWatch[] = [];

  for (const s of media.seasons) {
    if (s.seasonNumber > season.seasonNumber) {
      break;
    }

    const watchedEpisodeNumbers = s.episodes.filter(
      (e) =>
        e.seasonNumber < season.seasonNumber ||
        (e.seasonNumber === season.seasonNumber && e.episodeNumber <= episode.episodeNumber),
    );

    const watchedSeason = watched.seasons.find((ws) => compareID(ws.seasonID, s._id));

    watchedEpisodes.push(
      ...watchedEpisodeNumbers.filter(
        (v) => !watchedSeason?.watchedEpisodeNumbers?.includes(v.episodeNumber),
      ),
    );

    watchedSeasons.push({
      seasonID: String(s?._id?.toString()),
      watchedEpisodeNumbers: watchedEpisodeNumbers.map((e) => e.episodeNumber),
    });
  }
  return [watchedEpisodes, watchedSeasons];
};