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

DROP TRIGGER prevent_item_class_recursion ON item_classes;
DROP FUNCTION check_item_class_recursion_depth;

CREATE TYPE item_class_type AS ENUM ('generic', 'specific');

ALTER TABLE item_classes
  ADD type item_class_type;

UPDATE item_classes SET type='generic' WHERE parent IS NULL;
UPDATE item_classes SET type='specific' WHERE parent IS NOT NULL;

ALTER TABLE item_classes
  ALTER type SET NOT NULL;
ALTER TABLE item_classes
  ALTER type SET DEFAULT 'generic';

ALTER TABLE item_classes
  ADD CONSTRAINT parent_only_for_specific CHECK (type = 'generic' AND parent IS NULL OR type = 'specific' AND parent IS NOT NULL);

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

  IF (SELECT type FROM item_classes WHERE id = NEW.parent) = 'generic' THEN
    RETURN NEW;
  END IF;

  RAISE EXCEPTION 'Specific item classes may only have a generic parent (to avoid recursion)';
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER prevent_item_class_recursion
BEFORE INSERT OR UPDATE ON item_classes
FOR EACH ROW
EXECUTE FUNCTION check_item_class_parent();