create or replace function fsm.trig_check_no_state_loops()
returns trigger as
$$
declare the_cycle text[];
begin

  with recursive chart as (
    select distinct statechart_id
    from changed
  )
  , prev as (
    select cs.statechart_id, cs.id, array[id] as seen, false as cycle
    from fsm.state cs
    join chart
      on  chart.statechart_id = cs.statechart_id
    where parent_id is null

    union all

    select cs.statechart_id, cs.id, seen || cs.id as seen,
        cs.id = any(seen) as cycle
    from prev
    join fsm.state cs
      on  cs.statechart_id = prev.statechart_id
      and cs.parent_id = prev.id
      and prev.cycle = false
    join chart
      on  chart.statechart_id = cs.statechart_id
  )
  select seen into the_cycle
  from prev
  where prev.cycle
  limit 1;

  if the_cycle is not null
  then
    raise exception 'compound states should form a directed graph. Cycle detected: %', the_cycle;
  end if;

  return null;
end;
$$ language plpgsql;

comment on function fsm.trig_check_no_state_loops is $comment$
    Checks that the compound states do not form a cycle. Compound states
    should form a directed graph.
$comment$;

set client_min_messages TO warning;
drop trigger if exists check_no_state_loops_insert on fsm.state;
drop trigger if exists check_no_state_loops_update on fsm.state;
reset client_min_messages;

create trigger check_no_state_loops_insert
after insert
on fsm.state
referencing new table as changed
for each statement
execute function fsm.trig_check_no_state_loops();

comment on trigger check_no_state_loops_insert on fsm.state is $comment$
    Checks that the compound states do not form a cycle. Compound states
    should form a directed graph.
$comment$;

create trigger check_no_state_loops_update
after update
on fsm.state
referencing new table as changed
for each statement
execute function fsm.trig_check_no_state_loops();

comment on trigger check_no_state_loops_update on fsm.state is $comment$
    Checks that the compound states do not form a cycle. Compound states
    should form a directed graph.
$comment$;