class RouteSubscriber

class RouteSubscriber extends RouteSubscriberBase {
    
    /**
     * The entity type manager service.
     *
     * @var \Drupal\Core\Entity\EntityTypeManagerInterface
     */
    protected $entityTypeManager;
    
    /**
     * Constructs a new RouteSubscriber object.
     *
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_manager
     *   The entity type manager.
     */
    public function __construct(EntityTypeManagerInterface $entity_manager) {
        $this->entityTypeManager = $entity_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function alterRoutes(RouteCollection $collection) {
        foreach ($this->entityTypeManager
            ->getDefinitions() as $entity_type_id => $entity_type) {
            if ($route = $this->getEntityCloneRoute($entity_type)) {
                $collection->add("entity.{$entity_type_id}.clone_form", $route);
            }
        }
    }
    
    /**
     * Gets the entity_clone route.
     *
     * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
     *   The entity type.
     *
     * @return \Symfony\Component\Routing\Route|null
     *   The generated route, if available.
     */
    protected function getEntityCloneRoute(EntityTypeInterface $entity_type) {
        if ($clone_form = $entity_type->getLinkTemplate('clone-form')) {
            $entity_type_id = $entity_type->id();
            $route = new Route($clone_form);
            $route->addDefaults([
                '_form' => '\\Drupal\\entity_clone\\Form\\EntityCloneForm',
                '_title' => 'Clone ' . $entity_type->getLabel(),
            ])
                ->addRequirements([
                '_entity_access' => $entity_type_id . '.clone',
            ])
                ->setOption('_entity_clone_entity_type_id', $entity_type_id)
                ->setOption('_admin_route', TRUE)
                ->setOption('parameters', [
                $entity_type_id => [
                    'type' => 'entity:' . $entity_type_id,
                ],
            ]);
            // Special case for menu link content.
            // Menu link content does not work properly with custom operation.
            // This case must be removed when issue #3016038
            // (https://www.drupal.org/project/drupal/issues/3016038) was closed.
            if ($entity_type_id === 'menu_link_content') {
                $route->setRequirements([
                    '_permission' => 'clone ' . $entity_type_id . ' entity',
                ]);
            }
            return $route;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents() : array {
        $events = parent::getSubscribedEvents();
        $events[RoutingEvents::ALTER] = 'onAlterRoutes';
        return $events;
    }

}