-- Missing-pair pass (M485). A track marked missing whose replacement is already
-- on disk under another row — most often a Lidarr quality upgrade, mp3 → flac at
-- a new path — is folded into that replacement, so its history moves across and
-- re-acquisition stops chasing music the library already has.
--
-- Move adoption (#2528) cannot catch these: it links a new file to a missing row
-- at the moment the file is first inserted, and the replacement arrives as a
-- re-encode with no recording MBID, so it has nothing to match on. AcoustID may
-- give it an MBID later; by then both rows exist and only a fold can join them.

-- name: ListMissingTrackPairs :many
-- Every candidate (missing, present) pair, with how many candidates each side
-- has. Two rules, measured on the operator's library on 2026-10-07 (#5274):
--
--   mbid   the same recording MBID, within the album group (the album row, or
--          albums sharing a release group). 142 of 359 pairs.
--   title  the same album row and the same title, ignoring case. 213 more. The
--          replacements are often not the original file — another edition,
--          re-encoded, untagged — so the metadata is what is left to go on.
--
-- Deliberately NOT gated on duration or track position. On the 142 pairs known
-- to be one recording, 18% differed by over 2s (old mp3 durations are poor
-- estimates), and the poorly tagged set is exactly where numbering is broken.
--
-- A pair whose MBIDs are both set and differ is not a title match: the tags say
-- they are different recordings. The caller folds a pair only when each side has
-- exactly one candidate; anything else is ambiguous and left alone.
WITH grp AS (
  SELECT id AS album_id, COALESCE(release_group_mbid, id::text) AS g
    FROM albums
),
cand AS (
  SELECT m.id AS missing_id, p.id AS present_id, 'mbid'::text AS rule
    FROM tracks m
    JOIN grp gm ON gm.album_id = m.album_id
    JOIN grp gp ON gp.g = gm.g
    JOIN tracks p ON p.album_id = gp.album_id
                 AND p.missing_since IS NULL
                 AND p.mbid = m.mbid
   WHERE m.missing_since IS NOT NULL
     AND m.mbid IS NOT NULL
  UNION ALL
  SELECT m.id, p.id, 'title'::text
    FROM tracks m
    JOIN tracks p ON p.album_id = m.album_id
                 AND p.missing_since IS NULL
                 AND lower(p.title) = lower(m.title)
   WHERE m.missing_since IS NOT NULL
     AND (m.mbid IS NULL OR p.mbid IS NULL OR m.mbid = p.mbid)
),
pairs AS (
  -- A pair both rules found is one candidate, credited to the stronger rule.
  SELECT missing_id, present_id, min(rule)::text AS rule
    FROM cand
   GROUP BY missing_id, present_id
)
SELECT pr.missing_id, pr.present_id, pr.rule,
       m.file_path AS missing_path, p.file_path AS present_path,
       (count(*) OVER (PARTITION BY pr.missing_id))::int AS missing_candidates,
       (count(*) OVER (PARTITION BY pr.present_id))::int AS present_candidates
  FROM pairs pr
  JOIN tracks m ON m.id = pr.missing_id
  JOIN tracks p ON p.id = pr.present_id
 ORDER BY m.file_path, p.file_path;

-- name: LockTracksForPairing :many
-- Locks both rows of a pair for the fold's transaction, in id order so two
-- passes cannot deadlock, and returns what the fold re-checks: the missing row
-- must still be missing and the present one still present. A scan may have
-- restored or adopted the first, or marked the second, since the pairs were listed.
SELECT id, missing_since
  FROM tracks
 WHERE id = ANY(sqlc.arg(ids)::uuid[])
 ORDER BY id
   FOR UPDATE;