How to change Howdy text and use conditional text in wp site

/*
* Main Post: http://www.pchelpcenterbd.com/wordpress-development-12813
* Coded by: Md Abul Bashar
*/
function public_holiday() {
    $date = date('d-m');
    switch($date) {
        case '01-01':
            $message = 'Happy New Years ';
        break;

        case '02-06':
            $message = 'Happy Sobeborat Mobarak ';
        break;


        case '18-06':
            $message = 'Happy Romadan Mobarak ';
        break;

        case '18-07':
            $message = 'Eid Mobarak ';
        break;

        default:
            $message = 'Welcome to ';
    }
    return $message;
}

function howdy_message($translated_text, $text, $domain) {
    $message = public_holiday();
    $new_message = str_replace('Howdy', $message, $text);
    return $new_message;
}

add_filter('gettext', 'howdy_message', 10, 3);