-- SPDX-FileCopyrightText: 2024 Simon Bruder <simon@sbruder.de>
--
-- SPDX-License-Identifier: AGPL-3.0-or-later

ALTER TABLE items
  ADD parent UUID REFERENCES items(id);

CREATE RECURSIVE VIEW item_tree (id, parents) AS (
  SELECT id, ARRAY[]::UUID[] AS parents FROM items WHERE parent IS NULL
  UNION
  SELECT items.id, item_tree.parents || items.parent FROM items, item_tree WHERE items.parent = item_tree.id
);

CREATE FUNCTION check_item_cycle()
RETURNS TRIGGER AS $$
BEGIN
  IF NEW.parent IS NULL THEN
    RETURN NEW;
  END IF;

  IF NEW.id = NEW.parent THEN
    RAISE EXCEPTION 'Cycle detected';
  END IF;

  IF (WITH RECURSIVE cte AS (
    SELECT id, parent
    FROM items
    WHERE id = NEW.parent

    UNION

    SELECT items.id, items.parent
    FROM items, cte
    WHERE items.id = cte.parent
  )
  SELECT 1
  FROM cte
  WHERE parent = NEW.id
  LIMIT 1) THEN
    RAISE EXCEPTION 'Cycle detected';
  END IF;

  RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER prevent_item_cycle
BEFORE INSERT OR UPDATE ON items
FOR EACH ROW
EXECUTE FUNCTION check_item_cycle();