class EntityAutocompleteController

class EntityAutocompleteController extends ControllerBase {
    
    /**
     * The autocomplete matcher for entity references.
     *
     * @var \Drupal\Core\Entity\EntityAutocompleteMatcherInterface
     */
    protected $matcher;
    
    /**
     * The key value store.
     *
     * @var \Drupal\Core\KeyValueStore\KeyValueStoreInterface
     */
    protected $keyValue;
    
    /**
     * Constructs an EntityAutocompleteController object.
     *
     * @param \Drupal\Core\Entity\EntityAutocompleteMatcherInterface $matcher
     *   The autocomplete matcher for entity references.
     * @param \Drupal\Core\KeyValueStore\KeyValueStoreInterface $key_value
     *   The key value factory.
     */
    public function __construct(EntityAutocompleteMatcherInterface $matcher, KeyValueStoreInterface $key_value) {
        $this->matcher = $matcher;
        $this->keyValue = $key_value;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('entity.autocomplete_matcher'), $container->get('keyvalue')
            ->get('entity_autocomplete'));
    }
    
    /**
     * Autocomplete the label of an entity.
     *
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object that contains the typed tags.
     * @param string $target_type
     *   The ID of the target entity type.
     * @param string $selection_handler
     *   The plugin ID of the entity reference selection handler.
     * @param string $selection_settings_key
     *   The hashed key of the key/value entry that holds the selection handler
     *   settings.
     *
     * @return \Symfony\Component\HttpFoundation\JsonResponse
     *   The matched entity labels as a JSON response.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException
     *   Thrown if the selection settings key is not found in the key/value store
     *   or if it does not match the stored data.
     */
    public function handleAutocomplete(Request $request, $target_type, $selection_handler, $selection_settings_key) {
        $matches = [];
        // Get the typed string from the URL, if it exists.
        $input = $request->query
            ->get('q');
        // Check this string for emptiness, but allow any non-empty string.
        if (is_string($input) && strlen($input)) {
            $tag_list = Tags::explode($input);
            $typed_string = !empty($tag_list) ? mb_strtolower(array_pop($tag_list)) : '';
            // Selection settings are passed in as a hashed key of a serialized array
            // stored in the key/value store.
            $selection_settings = $this->keyValue
                ->get($selection_settings_key, FALSE);
            if ($selection_settings !== FALSE) {
                $selection_settings_hash = Crypt::hmacBase64(serialize($selection_settings) . $target_type . $selection_handler, Settings::getHashSalt());
                if (!hash_equals($selection_settings_hash, $selection_settings_key)) {
                    // Disallow access when the selection settings hash does not match the
                    // passed-in key.
                    throw new AccessDeniedHttpException('Invalid selection settings key.');
                }
            }
            else {
                // Disallow access when the selection settings key is not found in the
                // key/value store.
                throw new AccessDeniedHttpException();
            }
            $entity_type_id = $request->query
                ->get('entity_type');
            if ($entity_type_id && $this->entityTypeManager()
                ->hasDefinition($entity_type_id)) {
                $entity_id = $request->query
                    ->get('entity_id');
                if ($entity_id) {
                    $entity = $this->entityTypeManager()
                        ->getStorage($entity_type_id)
                        ->load($entity_id);
                    if ($entity->access('update')) {
                        $selection_settings['entity'] = $entity;
                    }
                }
            }
            $matches = $this->matcher
                ->getMatches($target_type, $selection_handler, $selection_settings, $typed_string);
        }
        return new JsonResponse($matches);
    }

}