public function registerIndexSingleton()
    {
        $this->app->singleton(Index::class, function ($app) {

            $settings = new IndexSettings(
                config('elasticsearch.index'),
                config('elasticsearch.settings'),
                config('elasticsearch.mappings')
            );

            $settings->setIndexables(config('elasticsearch.indexables'));

            return new Index($app[Client::class], $settings);
        });
    }