--- /dev/null
+<?php
+
+namespace Drupal\book;
+
+use Drupal\Core\Breadcrumb\Breadcrumb;
+use Drupal\Core\Breadcrumb\BreadcrumbBuilderInterface;
+use Drupal\Core\Entity\EntityManagerInterface;
+use Drupal\Core\Link;
+use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\node\NodeInterface;
+
+/**
+ * Provides a breadcrumb builder for nodes in a book.
+ */
+class BookBreadcrumbBuilder implements BreadcrumbBuilderInterface {
+ use StringTranslationTrait;
+
+ /**
+ * The node storage.
+ *
+ * @var \Drupal\Core\Entity\EntityStorageInterface
+ */
+ protected $nodeStorage;
+
+ /**
+ * The current user account.
+ *
+ * @var \Drupal\Core\Session\AccountInterface
+ */
+ protected $account;
+
+ /**
+ * Constructs the BookBreadcrumbBuilder.
+ *
+ * @param \Drupal\Core\Entity\EntityManagerInterface $entity_manager
+ * The entity manager service.
+ * @param \Drupal\Core\Session\AccountInterface $account
+ * The current user account.
+ */
+ public function __construct(EntityManagerInterface $entity_manager, AccountInterface $account) {
+ $this->nodeStorage = $entity_manager->getStorage('node');
+ $this->account = $account;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function applies(RouteMatchInterface $route_match) {
+ $node = $route_match->getParameter('node');
+ return $node instanceof NodeInterface && !empty($node->book);
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function build(RouteMatchInterface $route_match) {
+ $book_nids = [];
+ $breadcrumb = new Breadcrumb();
+
+ $links = [Link::createFromRoute($this->t('Home'), '<front>')];
+ $book = $route_match->getParameter('node')->book;
+ $depth = 1;
+ // We skip the current node.
+ while (!empty($book['p' . ($depth + 1)])) {
+ $book_nids[] = $book['p' . $depth];
+ $depth++;
+ }
+ $parent_books = $this->nodeStorage->loadMultiple($book_nids);
+ if (count($parent_books) > 0) {
+ $depth = 1;
+ while (!empty($book['p' . ($depth + 1)])) {
+ if (!empty($parent_books[$book['p' . $depth]]) && ($parent_book = $parent_books[$book['p' . $depth]])) {
+ $access = $parent_book->access('view', $this->account, TRUE);
+ $breadcrumb->addCacheableDependency($access);
+ if ($access->isAllowed()) {
+ $breadcrumb->addCacheableDependency($parent_book);
+ $links[] = Link::createFromRoute($parent_book->label(), 'entity.node.canonical', ['node' => $parent_book->id()]);
+ }
+ }
+ $depth++;
+ }
+ }
+ $breadcrumb->setLinks($links);
+ $breadcrumb->addCacheContexts(['route.book_navigation']);
+ return $breadcrumb;
+ }
+
+}