class WorkflowAccessControlHandler

class WorkflowAccessControlHandler extends EntityAccessControlHandler implements EntityHandlerInterface {
  
  /**
   * The workflow type plugin manager.
   *
   * @var \Drupal\Component\Plugin\PluginManagerInterface
   */
  protected $workflowTypeManager;
  
  /**
   * {@inheritdoc}
   */
  public static function createInstance(ContainerInterface $container, EntityTypeInterface $entity_type) {
    return new static($entity_type, $container->get('plugin.manager.workflows.type'));
  }
  
  /**
   * Constructs the workflow access control handler instance.
   *
   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
   *   The entity type definition.
   * @param \Drupal\Component\Plugin\PluginManagerInterface $workflow_type_manager
   *   The workflow type plugin manager.
   */
  public function __construct(EntityTypeInterface $entity_type, PluginManagerInterface $workflow_type_manager) {
    parent::__construct($entity_type);
    $this->workflowTypeManager = $workflow_type_manager;
  }
  
  /**
   * {@inheritdoc}
   */
  protected function checkAccess(EntityInterface $entity, $operation, AccountInterface $account) {
    /** @var \Drupal\workflows\Entity\Workflow $entity */
    $workflow_type = $entity->getTypePlugin();
    if (strpos($operation, 'delete-state') === 0) {
      [, $state_id] = explode(':', $operation, 2);
      // Deleting a state is editing a workflow, but also we should forbid
      // access if there is only one state.
      return AccessResult::allowedIf(count($entity->getTypePlugin()
        ->getStates()) > 1)
        ->andIf(parent::checkAccess($entity, 'edit', $account))
        ->andIf(AccessResult::allowedIf(!in_array($state_id, $workflow_type->getRequiredStates(), TRUE)))
        ->addCacheableDependency($entity);
    }
    return parent::checkAccess($entity, $operation, $account);
  }
  
  /**
   * {@inheritdoc}
   */
  protected function checkCreateAccess(AccountInterface $account, array $context, $entity_bundle = NULL) {
    $workflow_types_count = count($this->workflowTypeManager
      ->getDefinitions());
    $admin_access = parent::checkCreateAccess($account, $context, $entity_bundle);
    // Allow access if there is at least one workflow type. Since workflow types
    // are provided by modules this is cacheable until extensions change.
    return $admin_access->andIf(AccessResult::allowedIf($workflow_types_count > 0))
      ->addCacheTags([
      'workflow_type_plugins',
    ]);
  }

}