class RouteSubscriber

class RouteSubscriber extends RouteSubscriberBase {
    
    /**
     * Stores a list of view,display IDs which haven't be used in the alter event.
     *
     * @var array
     */
    protected $viewsDisplayPairs;
    
    /**
     * The view storage.
     *
     * @var \Drupal\Core\Entity\EntityStorageInterface
     */
    protected $viewStorage;
    
    /**
     * The state key value store.
     *
     * @var \Drupal\Core\State\StateInterface
     */
    protected $state;
    
    /**
     * Stores an array of route names keyed by view_id.display_id.
     *
     * @var array
     */
    protected $viewRouteNames = [];
    
    /**
     * Constructs a \Drupal\views\EventSubscriber\RouteSubscriber instance.
     *
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager service.
     * @param \Drupal\Core\State\StateInterface $state
     *   The state key value store.
     */
    public function __construct(EntityTypeManagerInterface $entity_type_manager, StateInterface $state) {
        $this->viewStorage = $entity_type_manager->getStorage('view');
        $this->state = $state;
    }
    
    /**
     * Resets the internal state of the route subscriber.
     */
    public function reset() {
        $this->viewsDisplayPairs = NULL;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents() {
        $events = parent::getSubscribedEvents();
        $events[RoutingEvents::FINISHED] = [
            'routeRebuildFinished',
        ];
        // Ensure to run after the entity resolver subscriber
        // @see \Drupal\Core\EventSubscriber\EntityRouteAlterSubscriber
        $events[RoutingEvents::ALTER] = [
            'onAlterRoutes',
            -175,
        ];
        return $events;
    }
    
    /**
     * Gets all the views and display IDs using a route.
     */
    protected function getViewsDisplayIDsWithRoute() {
        if (!isset($this->viewsDisplayPairs)) {
            $this->viewsDisplayPairs = [];
            // @todo Convert this method to some service.
            $views = $this->getApplicableViews();
            foreach ($views as $data) {
                [
                    $view_id,
                    $display_id,
                ] = $data;
                $this->viewsDisplayPairs[] = $view_id . '.' . $display_id;
            }
            $this->viewsDisplayPairs = array_combine($this->viewsDisplayPairs, $this->viewsDisplayPairs);
        }
        return $this->viewsDisplayPairs;
    }
    
    /**
     * Returns a set of route objects.
     *
     * @return \Symfony\Component\Routing\RouteCollection
     *   A route collection.
     */
    public function routes() {
        $collection = new RouteCollection();
        foreach ($this->getViewsDisplayIDsWithRoute() as $pair) {
            [
                $view_id,
                $display_id,
            ] = explode('.', $pair);
            $view = $this->viewStorage
                ->load($view_id);
            // @todo This should have an executable factory injected.
            if (($view = $view->getExecutable()) && $view instanceof ViewExecutable) {
                if ($view->setDisplay($display_id) && ($display = $view->displayHandlers
                    ->get($display_id))) {
                    if ($display instanceof DisplayRouterInterface) {
                        $this->viewRouteNames += (array) $display->collectRoutes($collection);
                    }
                }
                $view->destroy();
            }
        }
        $this->state
            ->set('views.view_route_names', $this->viewRouteNames);
        return $collection;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function alterRoutes(RouteCollection $collection) {
        foreach ($this->getViewsDisplayIDsWithRoute() as $pair) {
            [
                $view_id,
                $display_id,
            ] = explode('.', $pair);
            $view = $this->viewStorage
                ->load($view_id);
            // @todo This should have an executable factory injected.
            if (($view = $view->getExecutable()) && $view instanceof ViewExecutable) {
                if ($view->setDisplay($display_id) && ($display = $view->displayHandlers
                    ->get($display_id))) {
                    if ($display instanceof DisplayRouterInterface) {
                        // If the display returns TRUE a route item was found, so it does not
                        // have to be added.
                        $view_route_names = $display->alterRoutes($collection);
                        $this->viewRouteNames = $view_route_names + $this->viewRouteNames;
                        foreach ($view_route_names as $id_display => $route_name) {
                            $view_route_name = $this->viewsDisplayPairs[$id_display];
                            unset($this->viewsDisplayPairs[$id_display]);
                            $collection->remove("views.{$view_route_name}");
                        }
                    }
                }
                $view->destroy();
            }
        }
    }
    
    /**
     * Stores the new route names after they have been rebuilt.
     *
     * Callback for the RoutingEvents::FINISHED event.
     *
     * @see \Drupal\views\EventSubscriber::getSubscribedEvents()
     */
    public function routeRebuildFinished() {
        $this->reset();
        $this->state
            ->set('views.view_route_names', $this->viewRouteNames);
    }
    
    /**
     * Returns all views/display combinations with routes.
     *
     * @see \Drupal\views\Views::getApplicableViews()
     */
    protected function getApplicableViews() {
        return Views::getApplicableViews('uses_route');
    }

}