public function shorten(Request $request)
    {
        $url =  Validator::make($request->all(), [
            'url' => 'url'
        ])->validate()['url'];

        $url_model = Url::firstOrNew(['url' => $url]);

        if ($success = $url_model->exists)

            // the model exists in the database .
            // we'll retrieve the shortend url and skip directly to displaying the view .
            $shortend_url = $url_model->shortend_url;

        elseif ($success = $url_model->save()) {

            // it does not exist, so we'll save it to retrieve the id assigned by the database .
            $shortend_url = env('APP_URL') . '/' . $url_model->id;
            $success = $url_model->update(compact('shortend_url'));
        }

        return view('result', compact('success', 'url', 'shortend_url'));
    }