-- name: InsertLibraryChange :exec
INSERT INTO library_changes (entity_type, entity_id, op)
VALUES ($1, $2, $3);

-- name: InsertLibraryChanges :exec
-- Batch form, for a mutation that touches many rows at once (the scan's
-- reconcile pass can mark up to a quarter of a library missing in one go). A
-- loop of single inserts would be thousands of round-trips inside a scan that
-- is already the slow path.
INSERT INTO library_changes (entity_type, entity_id, op)
SELECT sqlc.arg(entity_type)::text,
       unnest(sqlc.arg(entity_ids)::text[]),
       sqlc.arg(op)::text;

-- name: GetLibraryChangesSince :many
SELECT id, entity_type, entity_id, op, changed_at
FROM library_changes
WHERE id > $1
ORDER BY id ASC
LIMIT $2;

-- name: GetMaxLibraryChangeCursor :one
SELECT COALESCE(MAX(id), 0)::BIGINT FROM library_changes;

-- name: GetLastIssuedLibraryChangeCursor :one
-- The highest cursor this server has handed out, even once the compactor has
-- trimmed the rows: the id sequence's last value. A restored server's
-- sequence stands at the backup's last change.
SELECT COALESCE(pg_sequence_last_value(pg_get_serial_sequence('library_changes', 'id')::regclass), 0)::BIGINT;

-- name: GetLibraryChangesTrimmedThrough :one
-- The highest id of a delete the compactor has dropped. A cursor below it may
-- have missed that delete.
SELECT through FROM library_changes_trimmed;

-- name: DeleteSupersededLibraryChanges :execrows
-- Removes every row a newer row for the same entity has superseded. An app
-- reading from any cursor still meets the newer row, so it loses nothing.
DELETE FROM library_changes old
 WHERE EXISTS (SELECT 1 FROM library_changes newer
                WHERE newer.entity_type = old.entity_type
                  AND newer.entity_id = old.entity_id
                  AND newer.id > old.id);

-- name: DeleteOldLibraryDeletes :one
-- Removes deletes older than the cutoff and raises the trimmed mark past the
-- highest one, so an app whose cursor is below it starts over. Returns how
-- many went.
WITH gone AS (
    DELETE FROM library_changes WHERE op = 'delete' AND changed_at < $1 RETURNING id
), mark AS (
    UPDATE library_changes_trimmed
       SET through = GREATEST(through, (SELECT COALESCE(max(id), 0) FROM gone))
)
SELECT count(*)::BIGINT FROM gone;