-- Enforce case-insensitive genre uniqueness, matching `authors` and `tags`
-- (both got `UNIQUE (lower(name))` in 0009). `genres` only had a case-SENSITIVE
-- `name UNIQUE`, but the crawler's `sync_genres` treats genres as
-- case-insensitive (`WHERE lower(name) = lower($1)`) and can INSERT a new row
-- from a source string. Under a race (or across ticks) two different-cased
-- strings — "Isekai" vs "isekai" — could both miss the pre-check and both
-- insert, since the exact-name unique doesn't collide. That leaves duplicate
-- genre rows for one logical genre.

-- Heal any pre-existing case-variant duplicates before adding the index, so
-- `sqlx::migrate!` can't crash on a dirty table (mirrors 0031's pre-dedup).
-- Keep the lowest id per lower(name) as canonical and repoint manga_genres.
UPDATE manga_genres mg
   SET genre_id = d.keep_id
  FROM (
        SELECT g.id AS dup_id, k.keep_id
          FROM genres g
          JOIN (SELECT lower(name) AS lname, (array_agg(id ORDER BY id))[1] AS keep_id
                  FROM genres GROUP BY lower(name)) k
            ON lower(g.name) = k.lname AND g.id <> k.keep_id
       ) d
 WHERE mg.genre_id = d.dup_id
   AND NOT EXISTS (
        SELECT 1 FROM manga_genres x
         WHERE x.manga_id = mg.manga_id AND x.genre_id = d.keep_id
   );

-- Drop links that would have collided with the canonical link (already present).
DELETE FROM manga_genres mg
 USING (
        SELECT g.id AS dup_id
          FROM genres g
          JOIN (SELECT lower(name) AS lname, (array_agg(id ORDER BY id))[1] AS keep_id
                  FROM genres GROUP BY lower(name)) k
            ON lower(g.name) = k.lname AND g.id <> k.keep_id
       ) d
 WHERE mg.genre_id = d.dup_id;

-- Remove the now-orphaned duplicate genre rows.
DELETE FROM genres g
 USING (SELECT lower(name) AS lname, (array_agg(id ORDER BY id))[1] AS keep_id
          FROM genres GROUP BY lower(name)) k
 WHERE lower(g.name) = k.lname AND g.id <> k.keep_id;

CREATE UNIQUE INDEX genres_name_lower_uniq ON genres (lower(name));