$_SERVER['HTTP_REFERER'] How can I match it against all possibilities of a single domain?

This is probably quite hard to explain, so I'll try to make it as simple as possible:

Here's my code:

<?php

$ref = $_SERVER['HTTP_REFERER'];

switch($ref) {
    case "http://www.facebook.com":
    $ref_name = "Facebook";
    break;
    case "http://www.twitter.com":
    $ref_name = "Twitter";
    break;
}

?>

From what I know, HTTP_REFERER pulls the entire referrer url (e.g. www.facebook.com/abc/xyz/mno=prq) as oppose to the top-level domain. I'd like to be able to match $ref against something so that all referrer's whether from say http://static.facebook.com (a sub-domain) o开发者_JAVA百科r http://www.facebook.com/profile_id/bla (a url with additional folders and parameters after the top-level domain) are given the value of "http://www.facebook.com".

What's the most simple and effective way to do so?

Any comments/answers etc will be greatly appreciated :)!!

See: parse_url

$ref = 'http://static.facebook.com';

$host = implode('.', array_slice(explode('.', parse_url($ref, PHP_URL_HOST)), -2));
switch ($host) {
    case 'facebook.com':
        break;

    case 'twitter.com':
        break;
}

Update: Have a look at Root Zone Database if you're dealing with special TLDs.