create table fsm.state_machine_event (
  shard_id bigint not null,
  id bigint not null generated by default as identity ( start with 1 cache 32767 ),
  state_machine_id bigint not null,
  created_at timestamptz not null default now(),
  handled_at timestamptz,
  name text not null,
  data jsonb not null,

  primary key (shard_id, id),

  constraint created_should_be_before_handled
    check (created_at <= handled_at),

  constraint fk_state_machine
    foreign key(shard_id, state_machine_id)
    references fsm.state_machine(shard_id, id)
    on delete cascade
);

create index idx_state_machine on fsm.state_machine_event(shard_id, state_machine_id)
  where handled_at is null;

comment on table fsm.state_machine_event is
    'Queue of events that need to be processed for the state machine.';

comment on column fsm.state_machine_event.created_at is $comment$
    The timestamp when this event was created. The timestamp should be
    before "handled_at".
$comment$;

comment on column fsm.state_machine_event.handled_at is $comment$
    The timestamp when this event was handled. The timestamp should be
    after "created_at".
$comment$;

comment on column fsm.state_machine_event.data is $comment$
    The data to be sent to the callback handlers in on_entry, on_exit.
$comment$;