Get domain name

I was looking at the ecmall core file ecmall.php and saw that this function was written more clearly. I took it out and shared it.

function get_domain() {
 /* protocol*/
 $protocol = (isset($_SERVER['HTTPS']) && (strtolower($_SERVER['HTTPS']) != 'off')) ? 'https://' : 'http://';

 /* Domain name or IP address*/
 if (isset($_SERVER['HTTP_X_FORWARDED_HOST'])) {
 $host = $_SERVER['HTTP_X_FORWARDED_HOST'] ;
 } elseif (isset($_SERVER['HTTP_HOST'])) {
 $host = $_SERVER['HTTP_HOST'];
 } else {
 /* port*/
 if (isset($_SERVER['SERVER_PORT' ])) {
 $port = ':' . $_SERVER['SERVER_PORT'];
 if ((':80' == $port && 'http://' == $protocol) || (':443 ' == $port && 'https://' == $protocol)) {
 $port = '';
 }
 } else {
 $port = '';
 }

 if (isset($_SERVER[ 'SERVER_NAME'])) {
 $host = $_SERVER['SERVER_NAME'] . $port;
 } elseif (isset($_SERVER['SERVER_ADDR'])) {
 $host = $_SERVER['SERVER_ADDR'] . $port;
 }
 }

 return $protocol . $host;
}