Phosphorus and Lime

// get base domain (domain.tld)
/*____________________________________________________________________________*/
function get_base_domain($url)
{
$debug = 0;
$base_domain = '';

// generic tlds (source: http://en.wikipedia.org/wiki/Generic_top-level_domain)
$G_TLD = array(
'biz','com','edu','gov','info','int','mil','name','net','org',
'aero','asia','cat','coop','jobs','mobi','museum','pro','tel','travel',
'arpa','root',
'berlin','bzh','cym','gal','geo','kid','kids','lat','mail','nyc','post','sco','web','xxx',
'nato',
'example','invalid','localhost','test',
'bitnet','csnet','ip','local','onion','uucp',
'co' // note: not technically, but used in things like co.uk
);

// country tlds (source: http://en.wikipedia.org/wiki/Country_code_top-level_domain)
$C_TLD = array(
// active
'ac','ad','ae','af','ag','ai','al','am','an','ao','aq','ar','as','at','au','aw','ax','az',
'ba','bb','bd','be','bf','bg','bh','bi','bj','bm','bn','bo','br','bs','bt','bw','by','bz',
'ca','cc','cd','cf','cg','ch','ci','ck','cl','cm','cn','co','cr','cu','cv','cx','cy','cz',
'de','dj','dk','dm','do','dz','ec','ee','eg','er','es','et','eu','fi','fj','fk','fm','fo',
'fr','ga','gd','ge','gf','gg','gh','gi','gl','gm','gn','gp','gq','gr','gs','gt','gu','gw',
'gy','hk','hm','hn','hr','ht','hu','id','ie','il','im','in','io','iq','ir','is','it','je',
'jm','jo','jp','ke','kg','kh','ki','km','kn','kr','kw','ky','kz','la','lb','lc','li','lk',
'lr','ls','lt','lu','lv','ly','ma','mc','md','mg','mh','mk','ml','mm','mn','mo','mp','mq',
'mr','ms','mt','mu','mv','mw','mx','my','mz','na','nc','ne','nf','ng','ni','nl','no','np',
'nr','nu','nz','om','pa','pe','pf','pg','ph','pk','pl','pn','pr','ps','pt','pw','py','qa',
're','ro','ru','rw','sa','sb','sc','sd','se','sg','sh','si','sk','sl','sm','sn','sr','st',
'sv','sy','sz','tc','td','tf','tg','th','tj','tk','tl','tm','tn','to','tr','tt','tv','tw',
'tz','ua','ug','uk','us','uy','uz','va','vc','ve','vg','vi','vn','vu','wf','ws','ye','yu',
'za','zm','zw',
// inactive
'eh','kp','me','rs','um','bv','gb','pm','sj','so','yt','su','tp','bu','cs','dd','zr'
);


// get domain
if ( !$full_domain = get_url_domain($url) )
{
return $base_domain;
}

// now the fun

// break up domain, reverse
$DOMAIN = explode('.', $full_domain);
if ( $debug ) print_r($DOMAIN);
$DOMAIN = array_reverse($DOMAIN);
if ( $debug ) print_r($DOMAIN);

// first check for ip address
if ( count($DOMAIN) == 4 && is_numeric($DOMAIN[0]) && is_numeric($DOMAIN[3]) )
{
return $full_domain;
}

// if only 2 domain parts, that must be our domain
if ( count($DOMAIN) <= 2 ) return $full_domain;

/*
finally, with 3+ domain parts: obviously D0 is tld
now, if D0 = ctld and D1 = gtld, we might have something like com.uk
so, if D0 = ctld && D1 = gtld && D2 != 'www', domain = D2.D1.D0
else if D0 = ctld && D1 = gtld && D2 == 'www', domain = D1.D0
else domain = D1.D0
these rules are simplified below
*/
if ( in_array($DOMAIN[0], $C_TLD) && in_array($DOMAIN[1], $G_TLD) && $DOMAIN[2] != 'www' )
{
$full_domain = $DOMAIN[2] . '.' . $DOMAIN[1] . '.' . $DOMAIN[0];
}
else
{
$full_domain = $DOMAIN[1] . '.' . $DOMAIN[0];;
}

// did we succeed?
return $full_domain;
}
/*____________________________________________________________________________*/


// get domain from url
/*____________________________________________________________________________*/
function get_url_domain($url)
{
$domain = '';

$_URL = parse_url($url);

// sanity check
if ( empty($_URL) || empty($_URL['host']) )
{
$domain = '';
}
else
{
$domain = $_URL['host'];
}

return $domain;
}
/*____________________________________________________________________________*/


// Testbed
/*____________________________________________________________________________*/

if ( 1 )
{
// test code here
$TESTURL[] = 'http://127.0.0.1';
$TESTURL[] = 'http://www.examplesite.com.pk';
$TESTURL[] = 'http://domain.tv.com';
$TESTURL[] = 'http://domain.com.tv';
$TESTURL[] = 'http://domain.tv';
$TESTURL[] = 'http://domain.com';
$TESTURL[] = 'http://secure.email.website.co.uk';
$TESTURL[] = 'http://username:password@this.is.a.worst.shortly.subdomain.thisIsMyMainWebsite.com.cl';

foreach ( $TESTURL as $url )
{
echo $url . ' -> ' . get_base_domain($url) . '
';
}
}

/*____________________________________________________________________________*/

http://127.0.0.1 -> 127.0.0.1
http://www.examplesite.com.pk -> examplesite.com.pk
http://domain.tv.com -> tv.com
http://domain.com.tv -> domain.com.tv
http://domain.tv -> domain.tv
http://domain.com -> domain.com
http://secure.email.website.co.uk -> website.co.uk
http://username:password@this.is.a.worst.shortly.subdomain.thisIsMyMainWebsite.com.cl -> thisIsMyMainWebsite.com.cl