-- `cards.position` was a project-wide sort key. It is now a rank *within a
-- column* — the group of cards sharing a (project_id, status_id). The inbox
-- (status_id IS NULL) is its own column. The "all tasks" view no longer uses
-- position at all (it sorts alphabetically); ordering is a per-column concern
-- driven by PUT /api/projects/{id}/cards/order.

DROP INDEX IF EXISTS idx_cards_project_position;

CREATE INDEX IF NOT EXISTS idx_cards_project_status_position
    ON cards (project_id, status_id, position);

-- Re-pack every existing column to a dense 0..n-1, preserving current order.
-- The CTE is evaluated against the pre-update snapshot, so this is safe despite
-- writing the same table.
WITH ranked (id, rk) AS (
    SELECT id,
           row_number() OVER (
               PARTITION BY project_id, status_id
               ORDER BY position, id
           ) - 1
    FROM cards
)
UPDATE cards
SET position = (SELECT rk FROM ranked WHERE ranked.id = cards.id);