public function on(string $eventJson)
{
$data = json_decode($eventJson, true);
if (!array_key_exists('name', $data) || $data['name'] !== Events::CUSTOMER_PLACED_ORDER) {
throw UnknownEventException::unexpected(Events::CUSTOMER_PLACED_ORDER, $data['name']);
}
$this->orders->add(new Order(new OrderId($data['order_id']), new \DateTimeImmutable($data['date'])));
}