generate_code.php

<?php

function generateCode($id) {
    $codeStr = (1000000000 + $id) . generateRandomSerialNumber(4);

    return $codeStr . generateCheckDigit($codeStr);
}

function generateRandomSerialNumber($length)
{
    $vowels = '0123456789';
    $consonants = '0123456789';
    $password = '';
    $alt = time() % 2;
    for ($i = 0; $i < $length; $i++)
    {
        if ($alt == 1)
        {
            $password .= $consonants[(rand() % strlen($consonants))];
            $alt = 0;
        }
        else
        {
            $password .= $vowels[(rand() % strlen($vowels))];
            $alt = 1;
        }
    }

    return $password;
}

function generateCheckDigit($codeStr) {
    $odd_total = 0;
    $even_total = 0;
    $codeLength = strlen($codeStr);
    for ($i  =0; $i < $codeLength; $i++)
    {
        if ((($i+1)%2) == 0) {
            $even_total += $codeStr[$i];
        } else {
            $odd_total += $codeStr[$i];
        }
    }
    $sum = (3 * $odd_total) + $even_total;
    $check_digit = $sum % 10;

    return ($check_digit > 0) ? 10 - $check_digit : $check_digit;
}