class EntryPoint

class EntryPoint extends ControllerBase {

  /**
   * The JSON:API resource type repository.
   *
   * @var \Drupal\jsonapi\ResourceType\ResourceTypeRepositoryInterface
   */
  protected $resourceTypeRepository;

  /**
   * The account object.
   *
   * @var \Drupal\Core\Session\AccountInterface
   */
  protected $user;

  /**
   * EntryPoint constructor.
   *
   * @param \Drupal\jsonapi\ResourceType\ResourceTypeRepositoryInterface $resource_type_repository
   *   The resource type repository.
   * @param \Drupal\Core\Session\AccountInterface $user
   *   The current user.
   */
  public function __construct(ResourceTypeRepositoryInterface $resource_type_repository, AccountInterface $user) {
    $this->resourceTypeRepository = $resource_type_repository;
    $this->user = $user;
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    return new static($container
      ->get('jsonapi.resource_type.repository'), $container
      ->get('current_user'));
  }

  /**
   * Controller to list all the resources.
   *
   * @return \Drupal\jsonapi\ResourceResponse
   *   The response object.
   */
  public function index() {
    $cacheability = (new CacheableMetadata())
      ->addCacheContexts([
      'user.roles:authenticated',
    ])
      ->addCacheTags([
      'jsonapi_resource_types',
    ]);

    // Only build URLs for exposed resources.
    $resources = array_filter($this->resourceTypeRepository
      ->all(), function ($resource) {
      return !$resource
        ->isInternal();
    });
    $self_link = new Link(new CacheableMetadata(), Url::fromRoute('jsonapi.resource_list'), 'self');
    $urls = array_reduce($resources, function (LinkCollection $carry, ResourceType $resource_type) {
      if ($resource_type
        ->isLocatable() || $resource_type
        ->isMutable()) {
        $route_suffix = $resource_type
          ->isLocatable() ? 'collection' : 'collection.post';
        $url = Url::fromRoute(sprintf('jsonapi.%s.%s', $resource_type
          ->getTypeName(), $route_suffix))
          ->setAbsolute();

        // Using a resource type name in place of a link relation type is not
        // technically valid. However, since it matches the link key, it will
        // not actually be serialized since the rel is omitted if it matches the
        // link key; because of that no client can rely on it. Once an extension
        // relation type is implemented for links to a collection, that should
        // be used instead. Unfortunately, the `collection` link relation type
        // would not be semantically correct since it would imply that the
        // entrypoint is a *member* of the link target.
        // @todo: implement an extension relation type to signal that this is a primary collection resource.
        $link_relation_type = $resource_type
          ->getTypeName();
        return $carry
          ->withLink($resource_type
          ->getTypeName(), new Link(new CacheableMetadata(), $url, $link_relation_type));
      }
      return $carry;
    }, new LinkCollection([
      'self' => $self_link,
    ]));
    $meta = [];
    if ($this->user
      ->isAuthenticated()) {
      $current_user_uuid = $this
        ->entityTypeManager()
        ->getStorage('user')
        ->load($this->user
        ->id())
        ->uuid();
      $meta['links']['me'] = [
        'meta' => [
          'id' => $current_user_uuid,
        ],
      ];
      $cacheability
        ->addCacheContexts([
        'user',
      ]);
      try {
        $me_url = Url::fromRoute('jsonapi.user--user.individual', [
          'entity' => $current_user_uuid,
        ])
          ->setAbsolute()
          ->toString(TRUE);
        $meta['links']['me']['href'] = $me_url
          ->getGeneratedUrl();

        // The cacheability of the `me` URL is the cacheability of that URL
        // itself and the currently authenticated user.
        $cacheability = $cacheability
          ->merge($me_url);
      } catch (RouteNotFoundException $e) {

        // Do not add the link if the route is disabled or marked as internal.
      }
    }
    $response = new CacheableResourceResponse(new JsonApiDocumentTopLevel(new ResourceObjectData([]), new NullIncludedData(), $urls, $meta));
    return $response
      ->addCacheableDependency($cacheability);
  }

}