<?php

namespace Drupal\MYMODULE\EventSubscriber;

use Drupal\Core\Routing\RouteSubscriberBase;
use Symfony\Cmf\Component\Routing\RouteObjectInterface;
use Symfony\Component\HttpKernel\Event\GetResponseEvent;
use Symfony\Component\HttpKernel\KernelEvents;
use Symfony\Component\Routing\RouteCollection;

/**
 * Adds the unused parameters of the regular taxonomy overview to the current
 * route match object when it is the airports view so that other routes
 * (specifically, for the Devel load local task) can still find them.
 */
class RouteSubscriber extends RouteSubscriberBase {

  /**
   * Adds default to the airport view to match the original vocabulary overview.
   *
   * @param \Symfony\Component\Routing\RouteCollection $collection
   *   The route collection for adding routes.
   */
  protected function alterRoutes(RouteCollection $collection) {
    if ($route = $collection->get('view.airports.page_1')) {
      $route->setDefault('taxonomy_vocabulary', 'airports');
    }
  }

  /**
   * Adds variables to the current route match object if it is the airport view.
   *
   * @param \Symfony\Component\HttpKernel\Event\GetResponseEvent $event
   *   The response event, which contains the current request.
   */
  public function onKernelRequest(GetResponseEvent $event) {
    $request = $event->getRequest();
    // Deliberately avoid calling \Drupal::routeMatch()->getRouteName() because
    // that will instantiate a protected route match object that will not have
    // the raw variable we want to add.
    if ($request->attributes->get(RouteObjectInterface::ROUTE_NAME) === 'view.airports.page_1') {
      if ($raw = $request->attributes->get('_raw_variables', array())) {
        $raw->add(array('taxonomy_vocabulary' => 'airports'));
        $request->attributes->set('_raw_variables', $raw);
      }
    }
  }

  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents() {
    $events = parent::getSubscribedEvents();

    // The route object attribute will have been set in
    // router_listener::onKernelRequest(), which has a priority of 32.
    $events[KernelEvents::REQUEST][] = array('onKernelRequest', 31);

    return $events;
  }

}