Coupon generation

Coupon.php

    /**
     * @return string
     */
    protected function generateCode()
    {
        $length = 8;
        $code = "";

        $possible = "2346789234567891234567892345678923456789234567892345678923456789234567892345678923456789abcdfghjkmnpqrtvwxyzABCDFGHJKLMNPQRTVWXYZ";
        $maxlength = strlen($possible);

        if ($length > $maxlength) {
            $length = $maxlength;
        }

        $i = 0;
        while ($i < $length) {
            $char = substr($possible, mt_rand(0, $maxlength - 1), 1);
            if (!strstr($code, $char)) {
                $code .= $char;
                $i++;
            }
        }

        return $code;
    }