BookNavigationCacheContext.php

<?php

namespace Drupal\book\Cache;

use Drupal\Core\Cache\CacheableMetadata;
use Drupal\Core\Cache\Context\CacheContextInterface;
use Symfony\Component\DependencyInjection\ContainerAwareInterface;
use Symfony\Component\DependencyInjection\ContainerAwareTrait;
use Symfony\Component\HttpFoundation\RequestStack;

/**
 * Defines the book navigation cache context service.
 *
 * Cache context ID: 'route.book_navigation'.
 *
 * This allows for book navigation location-aware caching. It depends on:
 * - whether the current route represents a book node at all
 * - and if so, where in the book hierarchy we are
 *
 * This class is container-aware to avoid initializing the 'book.manager'
 * service when it is not necessary.
 */
class BookNavigationCacheContext implements CacheContextInterface, ContainerAwareInterface {
    use ContainerAwareTrait;
    
    /**
     * The request stack.
     *
     * @var \Symfony\Component\HttpFoundation\RequestStack
     */
    protected $requestStack;
    
    /**
     * Constructs a new BookNavigationCacheContext service.
     *
     * @param \Symfony\Component\HttpFoundation\RequestStack $request_stack
     *   The request stack.
     */
    public function __construct(RequestStack $request_stack) {
        $this->requestStack = $request_stack;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getLabel() {
        return t("Book navigation");
    }
    
    /**
     * {@inheritdoc}
     */
    public function getContext() {
        // Find the current book's ID.
        $current_bid = 0;
        if ($node = $this->requestStack
            ->getCurrentRequest()
            ->get('node')) {
            $current_bid = empty($node->book['bid']) ? 0 : $node->book['bid'];
        }
        // If we're not looking at a book node, then we're not navigating a book.
        if ($current_bid === 0) {
            return 'book.none';
        }
        // If we're looking at a book node, get the trail for that node.
        $active_trail = $this->container
            ->get('book.manager')
            ->getActiveTrailIds($node->book['bid'], $node->book);
        return implode('|', $active_trail);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCacheableMetadata() {
        // The book active trail depends on the node and data attached to it.
        // That information is however not stored as part of the node.
        $cacheable_metadata = new CacheableMetadata();
        if ($node = $this->requestStack
            ->getCurrentRequest()
            ->get('node')) {
            // If the node is part of a book then we can use the cache tag for that
            // book. If not, then it can't be optimized away.
            if (!empty($node->book['bid'])) {
                $cacheable_metadata->addCacheTags([
                    'bid:' . $node->book['bid'],
                ]);
            }
            else {
                $cacheable_metadata->setCacheMaxAge(0);
            }
        }
        return $cacheable_metadata;
    }

}