class RouteProviderLazyBuilder

class RouteProviderLazyBuilder implements PreloadableRouteProviderInterface, EventSubscriberInterface {
    
    /**
     * The route provider service.
     *
     * @var \Drupal\Core\Routing\RouteProviderInterface
     */
    protected $routeProvider;
    
    /**
     * The route building service.
     *
     * @var \Drupal\Core\Routing\RouteBuilderInterface
     */
    protected $routeBuilder;
    
    /**
     * Flag to determine if the router has been rebuilt.
     *
     * @var bool
     */
    protected $rebuilt = FALSE;
    
    /**
     * Flag to determine if router is currently being rebuilt.
     *
     * Used to prevent recursive router rebuilds during module installation.
     * Recursive rebuilds can occur when route information is required by alter
     * hooks that are triggered during a rebuild, for example,
     * hook_menu_links_discovered_alter().
     *
     * @var bool
     */
    protected $rebuilding = FALSE;
    
    /**
     * RouteProviderLazyBuilder constructor.
     *
     * @param \Drupal\Core\Routing\RouteProviderInterface $route_provider
     *   The route provider service.
     * @param \Drupal\Core\Routing\RouteBuilderInterface $route_builder
     *   The route building service.
     */
    public function __construct(RouteProviderInterface $route_provider, RouteBuilderInterface $route_builder) {
        $this->routeProvider = $route_provider;
        $this->routeBuilder = $route_builder;
    }
    
    /**
     * Gets the real route provider service and rebuilds the router id necessary.
     *
     * @return \Drupal\Core\Routing\RouteProviderInterface
     *   The route provider service.
     */
    protected function getRouteProvider() {
        if (!$this->rebuilt && !$this->rebuilding) {
            $this->routeBuilder
                ->rebuild();
        }
        return $this->routeProvider;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getRouteCollectionForRequest(Request $request) {
        return $this->getRouteProvider()
            ->getRouteCollectionForRequest($request);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getRouteByName($name) {
        return $this->getRouteProvider()
            ->getRouteByName($name);
    }
    
    /**
     * {@inheritdoc}
     */
    public function preLoadRoutes($names) {
        return $this->getRouteProvider()
            ->preLoadRoutes($names);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getRoutesByNames($names) {
        return $this->getRouteProvider()
            ->getRoutesByNames($names);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getRoutesByPattern($pattern) {
        return $this->getRouteProvider()
            ->getRoutesByPattern($pattern);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getAllRoutes() {
        return $this->getRouteProvider()
            ->getAllRoutes();
    }
    
    /**
     * {@inheritdoc}
     */
    public function reset() {
        // Don't call getRouteProvider as this is results in recursive rebuilds.
        return $this->routeProvider
            ->reset();
    }
    
    /**
     * Determines if the router has been rebuilt.
     *
     * @return bool
     *   TRUE is the router has been rebuilt, FALSE if not.
     */
    public function hasRebuilt() {
        return $this->rebuilt;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents() : array {
        $events[RoutingEvents::DYNAMIC][] = [
            'routerRebuilding',
            3000,
        ];
        $events[RoutingEvents::FINISHED][] = [
            'routerRebuildFinished',
            -3000,
        ];
        return $events;
    }
    
    /**
     * Sets the router rebuilding flag to TRUE.
     */
    public function routerRebuilding() {
        $this->rebuilding = TRUE;
    }
    
    /**
     * Sets the router rebuilding flag to FALSE.
     */
    public function routerRebuildFinished() {
        $this->rebuilding = FALSE;
        $this->rebuilt = TRUE;
    }

}