-- "You might like" Home rows (#790). The daily build computes ranked
-- album/artist IDs in Go (similarity roll-up + cold-start gate) and
-- atomic-replaces them here; /api/home reads them back hydrated.

-- name: CountListeningSignalForUser :one
-- Cold-start gate. Returns the breadth of the user's real listening:
-- distinct unskipped tracks played and distinct artists played. The
-- build skips You-might-like entirely below a threshold (a thin history
-- yields near-random roll-ups). was_skipped=false so a user spamming
-- next can't inflate the signal.
SELECT
    count(DISTINCT pe.track_id)::bigint AS distinct_tracks,
    count(DISTINCT t.artist_id)::bigint AS distinct_artists
FROM play_events pe
JOIN tracks t ON t.id = pe.track_id
WHERE pe.user_id = $1 AND pe.was_skipped = false;

-- name: DeleteYouMightLikeAlbumsForUser :exec
DELETE FROM you_might_like_albums WHERE user_id = $1;

-- name: InsertYouMightLikeAlbum :exec
INSERT INTO you_might_like_albums (user_id, album_id, rank)
VALUES ($1, $2, $3);

-- name: DeleteYouMightLikeArtistsForUser :exec
DELETE FROM you_might_like_artists WHERE user_id = $1;

-- name: InsertYouMightLikeArtist :exec
INSERT INTO you_might_like_artists (user_id, artist_id, rank)
VALUES ($1, $2, $3);

-- name: ListYouMightLikeAlbumsForUser :many
-- Read path. Same projection as ListRediscoverAlbumsForUser so the API
-- layer reuses albumRefFrom(row.Album, row.ArtistName, …). Ordered by
-- the rank persisted at build time. Final cross-section dedup (vs Most
-- Played / Rediscover) and the output cap land in the Go layer
-- (internal/recommendation/home.go).
SELECT sqlc.embed(albums), artists.name AS artist_name
FROM you_might_like_albums yml
JOIN albums  ON albums.id  = yml.album_id
JOIN artists ON artists.id = albums.artist_id
WHERE yml.user_id = $1
ORDER BY yml.rank
LIMIT $2;

-- name: ListYouMightLikeArtistsForUser :many
-- Read path. Same projection as ListRediscoverArtistsForUser (embeds the
-- artist + a representative cover_album_id + album_count) so the API
-- layer reuses artistRefFromCovered. Ordered by persisted rank.
SELECT sqlc.embed(artists),
       cov.id AS cover_album_id,
       cnt.album_count::bigint AS album_count
FROM you_might_like_artists yml
JOIN artists ON artists.id = yml.artist_id
LEFT JOIN LATERAL (
    SELECT id FROM albums
    WHERE artist_id = artists.id AND cover_art_path IS NOT NULL
    ORDER BY created_at DESC LIMIT 1
) cov ON true
LEFT JOIN LATERAL (
    SELECT count(*) AS album_count
    FROM albums WHERE artist_id = artists.id
) cnt ON true
WHERE yml.user_id = $1
ORDER BY yml.rank
LIMIT $2;
