-- M7 #352 slice 2: system-generated playlist queries.

-- name: ListActiveUsersForSystemPlaylists :many
-- Active = had a play in the last 7 days. The cron iterates this list.
SELECT u.id FROM users u
 WHERE EXISTS (
     SELECT 1 FROM play_events pe
      WHERE pe.user_id = u.id
        AND pe.started_at > now() - INTERVAL '7 days'
   );

-- name: GetSystemPlaylistRun :one
SELECT user_id, last_run_at, last_run_date, in_flight, last_error
  FROM system_playlist_runs
 WHERE user_id = $1;

-- name: TryClaimSystemPlaylistRun :one
-- Atomic test-and-set on in_flight. Returns the row if we won the claim,
-- or pgx.ErrNoRows if someone else is already building.
INSERT INTO system_playlist_runs (user_id, in_flight)
VALUES ($1, true)
ON CONFLICT (user_id) DO UPDATE
   SET in_flight = true
   WHERE system_playlist_runs.in_flight = false
RETURNING user_id, last_run_at, last_run_date, in_flight, last_error;

-- name: FinishSystemPlaylistRun :exec
-- Mark a successful build complete.
UPDATE system_playlist_runs
   SET last_run_at   = $2,
       last_run_date = $3,
       in_flight     = false,
       last_error    = NULL
 WHERE user_id = $1;

-- name: FailSystemPlaylistRun :exec
-- Mark a failed build complete (in_flight=false, error captured).
UPDATE system_playlist_runs
   SET in_flight  = false,
       last_error = $2
 WHERE user_id = $1;

-- name: ClearStaleSystemPlaylistInFlight :exec
-- Cron startup recovery: clear any in_flight=true rows from a previously
-- crashed process. Safe because at startup, by definition, nothing is
-- still building.
UPDATE system_playlist_runs SET in_flight = false WHERE in_flight = true;

-- name: PickSeedArtists :many
-- Top-5 most-engaged distinct artist candidates in the user's last 7
-- days. The Go-side picker (pickSeedArtistsForDay) shuffles these
-- daily-deterministically and takes the first 3 so the set of
-- "Songs like X" mixes rotates day-to-day.
-- Score = unskipped-play count + 5 if user has liked the artist.
WITH plays AS (
    SELECT t.artist_id,
           COUNT(*) FILTER (WHERE pe.was_skipped = false) AS play_count
      FROM play_events pe
      JOIN tracks t ON t.id = pe.track_id
     WHERE pe.user_id = $1
       AND pe.started_at > now() - INTERVAL '7 days'
       AND t.artist_id IS NOT NULL
     GROUP BY t.artist_id
),
liked AS (
    SELECT artist_id FROM general_likes_artists WHERE user_id = $1
)
SELECT p.artist_id,
       (p.play_count + CASE WHEN l.artist_id IS NOT NULL THEN 5 ELSE 0 END)::bigint AS score
  FROM plays p
  LEFT JOIN liked l ON l.artist_id = p.artist_id
 ORDER BY score DESC, p.artist_id
 LIMIT 5;

-- name: PickTopPlayedTracksForUser :many
-- For-You candidate seeds, tiered so For-You never silently vanishes:
--   tier 0  top non-skip plays in the last 30 days
--   tier 1  (only if tier 0 empty) all-time top non-skip plays
--   tier 2  (only if tiers 0+1 empty) liked tracks
-- Returns up to 5 ids; tie-break by track_id for determinism. The
-- Go-side picker (pickForYouSeedForDay) rotates one per day via
-- userIDHash. Widened from a hard 7-day window, which made For-You
-- disappear after a week of not listening and never recover on a
-- self-hosted library with sparse history.
WITH recent AS (
    SELECT t.id, COUNT(*) AS c, 0 AS tier
      FROM play_events pe
      JOIN tracks t ON t.id = pe.track_id
     WHERE pe.user_id = $1
       AND pe.started_at > now() - INTERVAL '30 days'
       AND pe.was_skipped = false
     GROUP BY t.id
),
alltime AS (
    SELECT t.id, COUNT(*) AS c, 1 AS tier
      FROM play_events pe
      JOIN tracks t ON t.id = pe.track_id
     WHERE pe.user_id = $1
       AND pe.was_skipped = false
     GROUP BY t.id
),
liked AS (
    SELECT gl.track_id AS id, 0::bigint AS c, 2 AS tier
      FROM general_likes gl
     WHERE gl.user_id = $1
),
chosen AS (
    SELECT id, c, tier FROM recent
    UNION ALL
    SELECT id, c, tier FROM alltime
     WHERE NOT EXISTS (SELECT 1 FROM recent)
    UNION ALL
    SELECT id, c, tier FROM liked
     WHERE NOT EXISTS (SELECT 1 FROM recent)
       AND NOT EXISTS (SELECT 1 FROM alltime)
)
SELECT id
  FROM chosen
 ORDER BY tier, c DESC, id
 LIMIT 5;

-- name: PickTopPlayedTrackForArtistByUser :one
-- "Songs like X" seed selection. Returns the user's most-played non-skipped
-- track by artist X in the last 7 days. Falls back to the artist's most-
-- recent album's first track if no plays exist.
-- Cast to uuid so sqlc infers pgtype.UUID rather than interface{}.
SELECT COALESCE(
    (SELECT t.id
       FROM play_events pe
       JOIN tracks t ON t.id = pe.track_id
      WHERE pe.user_id = $1
        AND t.artist_id = $2
        AND pe.started_at > now() - INTERVAL '7 days'
        AND pe.was_skipped = false
      GROUP BY t.id
      ORDER BY COUNT(*) DESC, t.id
      LIMIT 1),
    (SELECT t.id
       FROM tracks t
       JOIN albums a ON a.id = t.album_id
      WHERE t.artist_id = $2
      ORDER BY a.release_date DESC NULLS LAST,
               t.disc_number NULLS LAST,
               t.track_number NULLS LAST,
               t.id
      LIMIT 1)
)::uuid AS id;

-- name: PickTopAlbumCoverForArtistByUser :one
-- "Songs like X" cover. Most-played album by user; tie-break by most-recent
-- release. NULL if the artist has no albums or all covers are NULL.
-- Note: albums uses cover_art_path (not cover_path).
SELECT a.cover_art_path
  FROM albums a
  LEFT JOIN tracks t ON t.album_id = a.id
  LEFT JOIN play_events pe
    ON pe.track_id = t.id
   AND pe.user_id = $1
   AND pe.was_skipped = false
 WHERE a.artist_id = $2
   AND a.cover_art_path IS NOT NULL
 GROUP BY a.id, a.release_date, a.cover_art_path
 ORDER BY COUNT(pe.id) DESC, a.release_date DESC NULLS LAST, a.id
 LIMIT 1;

-- name: DeleteSystemPlaylistsForUser :exec
-- Atomic-replace step. CASCADE on playlist_tracks.playlist_id handles
-- the join rows.
DELETE FROM playlists WHERE user_id = $1 AND kind = 'system';

-- name: ListPlaylistsByUserAndKind :many
-- Used in integration tests; production filter applied in Go
-- (api.handleListPlaylists fetches via Service.List and filters by Kind in
-- memory so it can also surface other users' public playlists alongside
-- the caller's own kind-filtered ones).
-- Sorted by updated_at DESC.
SELECT id, user_id, name, description, is_public, kind, system_variant,
       seed_artist_id, cover_path, track_count, duration_sec,
       created_at, updated_at
  FROM playlists
 WHERE user_id = $1
   AND ($2::text = 'all' OR kind = $2)
 ORDER BY updated_at DESC;

-- name: CreateSystemPlaylist :one
-- Inserts a system-generated playlist. Used by BuildSystemPlaylists.
-- For 'for_you' variant, pass seed_artist_id as NULL (zero-value pgtype.UUID
-- with Valid=false).
INSERT INTO playlists (
    user_id, name, description, is_public,
    kind, system_variant, seed_artist_id, cover_path
) VALUES ($1, $2, '', false, 'system', $3, $4, $5)
RETURNING *;

-- name: GetSystemPlaylistByVariantForUser :one
-- Returns the user's system playlist for the given variant
-- ('for_you' / 'songs_like_artist' / 'discover'), or pgx.ErrNoRows
-- when the user hasn't built that variant yet. For
-- 'songs_like_artist' (which can have multiple rows per user, one
-- per seed), this returns whichever LIMIT 1 picks — callers that
-- need all instances should use a different query.
SELECT p.id, p.user_id, p.name, p.kind, p.system_variant,
       p.seed_artist_id, p.cover_path, p.track_count
  FROM playlists p
 WHERE p.user_id = $1
   AND p.kind = 'system'
   AND p.system_variant = $2
 ORDER BY p.created_at DESC
 LIMIT 1;
