Altering Entity Access - Disallow Editing Commerce Order

I had to block store owners from editing orders in Commerce after they're completed. I used hook_entity_access(), or more specifically hook_ENTITY_TYPE_access(), with the type commerce_order.

I put this function in my module file. It gets the order state and checks if it is completed, and if the operation is update. If so, it returns \Drupal\Core\Access\AccessResult::forbidden(). You can see more available responses here: AccessResult.

/**
 * Block access to order edit if state is completed.
 *
 * Implements hook_ENTITY_TYPE_access().
 */
function block_access_commerce_order_access(
  \Drupal\Core\Entity\EntityInterface $entity,
  $operation,
  \Drupal\Core\Session\AccountInterface $account) {

  $order = $entity;
  $properties = $order->getState()->getProperties();
  $state = $properties['value']->getValue();
  if ($state === 'completed' && $operation === 'update') {
    return \Drupal\Core\Access\AccessResult::forbidden();
  }
}

This has the effect of showing access denied on the edit page and hiding the edit tab on the order.