编辑代码

<?php 

function generate_random_code(int $length = 16, int $mode = 2)
{
    $randoms = [
        '0123456789',
        '0123456789abcdefhiklmnorstuvwxz',
        '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ',
    ];

    if ($mode > 2 || !is_int($mode)) {
        $mode = 2;
    }
    $codeSet = str_split($randoms[$mode]);
    $codeLen = count($codeSet) - 1;
    $nonceStr = '';
    for ($i = 0; $i < $length; $i++) {
        $nonceStr .= $codeSet[random_int(0, $codeLen)];
    }
    return $nonceStr;
}

var_dump('MG' . generate_random_code(16, 0));

var_dump(generate_random_code(32, 2));