class FormModeAccessCheck

class FormModeAccessCheck implements AccessInterface {
    
    /**
     * The entity type manager.
     *
     * @var \Drupal\Core\Entity\EntityTypeManagerInterface
     */
    protected $entityTypeManager;
    
    /**
     * Creates a new FormModeAccessCheck.
     *
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager.
     */
    public function __construct(EntityTypeManagerInterface $entity_type_manager) {
        $this->entityTypeManager = $entity_type_manager;
    }
    
    /**
     * Checks access to the form mode.
     *
     * @param \Symfony\Component\Routing\Route $route
     *   The route to check against.
     * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
     *   The parametrized route.
     * @param \Drupal\Core\Session\AccountInterface $account
     *   The currently logged in account.
     * @param string $form_mode_name
     *   (optional) The form mode. Defaults to 'default'.
     * @param string $bundle
     *   (optional) The bundle. Different entity types can have different names
     *   for their bundle key, so if not specified on the route via a {bundle}
     *   parameter, the access checker determines the appropriate key name, and
     *   gets the value from the corresponding request attribute. For example,
     *   for nodes, the bundle key is "node_type", so the value would be
     *   available via the {node_type} parameter rather than a {bundle}
     *   parameter.
     *
     * @return \Drupal\Core\Access\AccessResultInterface
     *   The access result.
     */
    public function access(Route $route, RouteMatchInterface $route_match, AccountInterface $account, $form_mode_name = 'default', $bundle = NULL) {
        $access = AccessResult::neutral();
        if ($entity_type_id = $route->getDefault('entity_type_id')) {
            if (empty($bundle)) {
                $entity_type = $this->entityTypeManager
                    ->getDefinition($entity_type_id);
                $bundle = $route_match->getRawParameter($entity_type->getBundleEntityType());
            }
            $visibility = FALSE;
            if ($form_mode_name == 'default') {
                $visibility = TRUE;
            }
            elseif ($entity_display = $this->entityTypeManager
                ->getStorage('entity_form_display')
                ->load($entity_type_id . '.' . $bundle . '.' . $form_mode_name)) {
                $visibility = $entity_display->status();
            }
            if ($form_mode_name != 'default' && $entity_display) {
                $access->addCacheableDependency($entity_display);
            }
            if ($visibility) {
                $permission = $route->getRequirement('_field_ui_form_mode_access');
                $access = $access->orIf(AccessResult::allowedIfHasPermission($account, $permission));
            }
        }
        return $access;
    }

}