uniqueCode.php

<?php
class helpers {
  public function uniqueCode($length = 10) {
        $characters = '0123456789';
        $charactersLength = strlen($characters);
        while (true) {
            // uniqid gives 13 chars, but you could adjust it to your needs.
            if (function_exists("random_bytes")) {
                $bytes = random_bytes($length);
            } elseif (function_exists("openssl_random_pseudo_bytes")) {
                $bytes = openssl_random_pseudo_bytes($length);
            } else {
                throw new Exception("no cryptographically secure random function available");
            }

            $code = '';
            for ($i = 0; $i < $length; $i++) {
                $code .= $characters[ord($bytes[$i]) % $charactersLength];
            }

            // check uniqueness by querying the DB
            //if (!$this->checkTicketCodeUniqueness($code)){
            //    break;
            //}
        }
        return $code;
    }
}