create or replace function fsm.trig_check_no_cross_boundary_transition() returns trigger as
$$
  declare
      bad_transitions jsonb;
  begin
    select jsonb_agg(c.*) into bad_transitions
    -- changed is the table of changes that where just modified
    from changed c
    join fsm.state source
      on  source.statechart_id = c.statechart_id
      and source.id = c.source_state
    join fsm.state target
      on  target.statechart_id = c.statechart_id
      and target.id = c.target_state
    where source.parent_id <> target.parent_id;

    if jsonb_array_length(bad_transitions) > 0
    then
      raise exception 'cannot add transitions between states with different parents: %', jsonb_pretty(bad_transitions);
    end if;

    return null;
  end;
$$ language plpgsql;

comment on function fsm.trig_check_no_cross_boundary_transition is $comment$
    This function checks that there are no transitions between states with
    different parents in the "fsm.transition" table.
$comment$;

set client_min_messages TO warning;
drop trigger if exists check_no_cross_boundary_transitions_insert on fsm.transition;
drop trigger if exists check_no_cross_boundary_transitions_update on fsm.transition;
reset client_min_messages;

create trigger check_no_cross_boundary_transitions_insert
after insert
on fsm.transition
referencing new table as changed
for each statement
execute function fsm.trig_check_no_cross_boundary_transition();

comment on trigger check_no_cross_boundary_transitions_insert on fsm.transition is $comment$
    Checks that no transitions in between states with different parents are
    inserted in the "fsm.transition" table.
$comment$;

create trigger check_no_cross_boundary_transitions_update
after update
on fsm.transition
referencing new table as changed
for each statement
execute function fsm.trig_check_no_cross_boundary_transition();

comment on trigger check_no_cross_boundary_transitions_update on fsm.transition is $comment$
    Checks that no transitions in between states with different parents are
    inserted in the "fsm.transition" table.
$comment$;