gistfile1.php

add_shortcode('list_domains_wpmu', 'list_domains_wpmu');
function list_domains_wpmu($attrs = array())
{
    $default = array(
        'root_domain' => parse_url(get_site_url(1), PHP_URL_HOST)
    );
    $a = wp_parse_args($attrs, $default);
    $domains = get_site_option('md_domains');
    $data = array();
    foreach ($domains as $domain) {
        $host = get_domain_5123($domain['domain_name']);
        if ($host != $a['root_domain']) {
            $data[] = sprintf('<a href="%s">%s</a>', $domain['domain_name'], $domain['domain_name']);
        }
    }
    echo implode('<br/>', $data);
}

function get_domain_5123($domain, $debug = false)
{
    $original = $domain = strtolower($domain);

    if (filter_var($domain, FILTER_VALIDATE_IP)) {
        return $domain;
    }

    $debug ? print('<strong style="color:green">&raquo;</strong> Parsing: ' . $original) : false;

    $arr = array_slice(array_filter(explode('.', $domain, 4), function ($value) {
        return $value !== 'www';
    }), 0); //rebuild array indexes

    if (count($arr) > 2) {
        $count = count($arr);
        $_sub = explode('.', $count === 4 ? $arr[3] : $arr[2]);

        $debug ? print(" (parts count: {$count})") : false;

        if (count($_sub) === 2) // two level TLD
        {
            $removed = array_shift($arr);
            if ($count === 4) // got a subdomain acting as a domain
            {
                $removed = array_shift($arr);
            }
            $debug ? print("<br>\n" . '[*] Two level TLD: <strong>' . join('.', $_sub) . '</strong> ') : false;
        } elseif (count($_sub) === 1) // one level TLD
        {
            $removed = array_shift($arr); //remove the subdomain

            if (strlen($_sub[0]) === 2 && $count === 3) // TLD domain must be 2 letters
            {
                array_unshift($arr, $removed);
            } else {
                // non country TLD according to IANA
                $tlds = array(
                    'aero',
                    'arpa',
                    'asia',
                    'biz',
                    'cat',
                    'com',
                    'coop',
                    'edu',
                    'gov',
                    'info',
                    'jobs',
                    'mil',
                    'mobi',
                    'museum',
                    'name',
                    'net',
                    'org',
                    'post',
                    'pro',
                    'tel',
                    'travel',
                    'xxx',
                );

                if (count($arr) > 2 && in_array($_sub[0], $tlds) !== false) //special TLD don't have a country
                {
                    array_shift($arr);
                }
            }
            $debug ? print("<br>\n" . '[*] One level TLD: <strong>' . join('.', $_sub) . '</strong> ') : false;
        } else // more than 3 levels, something is wrong
        {
            for ($i = count($_sub); $i > 1; $i--) {
                $removed = array_shift($arr);
            }
            $debug ? print("<br>\n" . '[*] Three level TLD: <strong>' . join('.', $_sub) . '</strong> ') : false;
        }
    } elseif (count($arr) === 2) {
        $arr0 = array_shift($arr);

        if (strpos(join('.', $arr), '.') === false
            && in_array($arr[0], array('localhost', 'test', 'invalid')) === false
        ) // not a reserved domain
        {
            $debug ? print("<br>\n" . 'Seems invalid domain: <strong>' . join('.', $arr) . '</strong> re-adding: <strong>' . $arr0 . '</strong> ') : false;
            // seems invalid domain, restore it
            array_unshift($arr, $arr0);
        }
    }

    $debug ? print("<br>\n" . '<strong style="color:gray">&laquo;</strong> Done parsing: <span style="color:red">' . $original . '</span> as <span style="color:blue">' . join('.', $arr) . "</span><br>\n") : false;

    return join('.', $arr);
}