Text - to_possessive

/*
     * Transform text to show ownership e.g Arvi's, Jess'
     */
    public function to_possessive($string)
    {
        $length = strlen($string);
        $last_letter = substr($string, $length-1, $length);
 
        $letter_s = ctype_upper($string) ? 'S' : 's';
 
        $possessive_form = ($last_letter == $letter_s) ? $string."'" : $string."'".$letter_s;
 
        return $possessive_form;
    }