-- 0013_series.sql — television: series, seasons, episodes.
--
-- Vellum had no season or episode model. media_items was a flat tree and the
-- scanner never parsed S01E02, so a library of television was a list of files
-- in a folder. That is the difference between a movie server and a media
-- server, and it is also what blocks TV metadata: there is nothing to attach a
-- series' poster or overview to.
--
-- Two decisions worth stating, because both are cheap now and expensive later.
--
--   * The new columns are additive and nullable. A film keeps NULL for both
--     numbers, so every existing row is untouched and every existing query, the
--     web app and the Jellyfin surface keep working exactly as they do today.
--     Nothing is rewritten, so there is no backfill and no migration risk.
--
--   * kind gains 'series' and 'season', but an EPISODE STAYS kind='video'. A
--     new 'episode' kind would mean touching every query that says video, for
--     no gain: the parent chain already tells an episode from a film, and a
--     series row is the only genuinely new concept. Keeping video also means a
--     library that has not been rescanned yet behaves identically.
--
-- A series and a season have no file of their own, so their path is the
-- directory they stand for. That is unique per library, which is what the
-- existing UNIQUE (library_id, path) requires, and it gives the row a stable
-- identity across rescans — the scanner can upsert on it rather than
-- duplicating a series every time it runs.
--
-- The tree itself is not new. parent_id already carries albums and audiobook
-- chapters, so this is the same shape applied to television: library -> series
-- -> season -> episode.

ALTER TABLE media_items ADD COLUMN season_number  INTEGER;
ALTER TABLE media_items ADD COLUMN episode_number INTEGER;

-- Listing a series' seasons and a season's episodes is the hot path, and both
-- read by parent and then order by the number.
CREATE INDEX idx_items_parent_season ON media_items(parent_id, season_number);

-- Finding every series in a library, and every season of one, without a scan.
CREATE INDEX idx_items_kind_parent ON media_items(kind, parent_id);