create or replace function fsm.trig_check_valid_initial_state() returns trigger as
$$
  declare
      chart bigint;
      total_initial bigint;
  begin
    for chart in
      select distinct statechart_id
      from changed
      where exists (select 1 from fsm.statechart where id = changed.statechart_id)
    loop
        select count(*) into total_initial
        from fsm.state
        where statechart_id = chart
          and is_initial
          and parent_id is null;

        if total_initial is distinct from 1
        then
          raise exception 'exactly one initial state is required per statechart';
        end if;

    end loop;

    return null;
  end;
$$ language plpgsql;

comment on function fsm.trig_check_valid_initial_state is $comment$
    Checks that there is only initial state per statechart. Only considers
    initial states whose parent_id is null.
$comment$;

set client_min_messages TO warning;
drop trigger if exists check_valid_initial_state_insert on fsm.state;
drop trigger if exists check_valid_initial_state_update on fsm.state;
drop trigger if exists check_valid_initial_state_delete on fsm.state;
reset client_min_messages;

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

comment on trigger check_valid_initial_state_insert on fsm.state is $comment$
    Checks that there is only initial state per statechart. Only considers
    initial states whose parent_id is null.
$comment$;

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

comment on trigger check_valid_initial_state_update on fsm.state is $comment$
    Checks that there is only initial state per statechart. Only considers
    initial states whose parent_id is null.
$comment$;

create trigger check_valid_initial_state_delete
after delete
on fsm.state
referencing old table as changed
for each statement
execute function fsm.trig_check_valid_initial_state();

comment on trigger check_valid_initial_state_delete on fsm.state is $comment$
    Checks that there is only initial state per statechart. Only considers
    initial states whose parent_id is null.
$comment$;