BEGIN;

CREATE OR REPLACE FUNCTION public.reorder_custom_instruction(
  instruction_id uuid,
  direction text
)
RETURNS SETOF public.custom_instructions
LANGUAGE plpgsql
SECURITY DEFINER
SET search_path = ''
AS $$
DECLARE
  current_user_id uuid := auth.uid();
  ordered_ids uuid[];
  current_index integer;
  target_index integer;
  swapped_id uuid;
BEGIN
  IF current_user_id IS NULL THEN
    RAISE EXCEPTION 'authentication_required' USING ERRCODE = '42501';
  END IF;
  IF direction NOT IN ('up', 'down') THEN
    RAISE EXCEPTION 'invalid_direction' USING ERRCODE = '22023';
  END IF;

  PERFORM pg_advisory_xact_lock(hashtextextended(current_user_id::text, 73036));
  SELECT array_agg(instruction.id ORDER BY instruction.sort_order, instruction.created_at, instruction.id)
    INTO ordered_ids
    FROM public.custom_instructions AS instruction
   WHERE instruction.user_id = current_user_id
     AND instruction.builtin_key IS NULL;

  current_index := array_position(ordered_ids, instruction_id);
  IF current_index IS NULL THEN
    RAISE EXCEPTION 'instruction_not_found' USING ERRCODE = 'P0002';
  END IF;
  target_index := current_index + CASE direction WHEN 'up' THEN -1 ELSE 1 END;
  IF target_index < 1 OR target_index > coalesce(array_length(ordered_ids, 1), 0) THEN
    RETURN QUERY
    SELECT instruction.*
      FROM public.custom_instructions AS instruction
     WHERE instruction.user_id = current_user_id
     ORDER BY instruction.sort_order, instruction.created_at, instruction.id;
    RETURN;
  END IF;

  swapped_id := ordered_ids[target_index];
  ordered_ids[target_index] := ordered_ids[current_index];
  ordered_ids[current_index] := swapped_id;

  UPDATE public.custom_instructions AS instruction
     SET sort_order = (ordering.ordinality * 10 + 1000)::integer
    FROM unnest(ordered_ids) WITH ORDINALITY AS ordering(id, ordinality)
   WHERE instruction.id = ordering.id
     AND instruction.user_id = current_user_id
     AND instruction.builtin_key IS NULL;

  RETURN QUERY
  SELECT instruction.*
    FROM public.custom_instructions AS instruction
   WHERE instruction.user_id = current_user_id
   ORDER BY instruction.sort_order, instruction.created_at, instruction.id;
END;
$$;

REVOKE ALL ON FUNCTION public.reorder_custom_instruction(uuid, text) FROM PUBLIC;
GRANT EXECUTE ON FUNCTION public.reorder_custom_instruction(uuid, text) TO authenticated;

COMMIT;