<?php

function enofollow($content)
{
	return preg_replace_callback('/<a[^>]+/', 'callback', $content);
}

function callback($matches)
{
	$link = $matches[0];
	$site_link = 'http://' . $_SERVER["SERVER_NAME"].$_SERVER["REQUEST_URI"];

	if (strpos($link, 'rel') === false) {
		$link = preg_replace("%(href=\S(?!$site_link))%i", 'rel="nofollow" $1', $link);
	} elseif (preg_match("%href=\S(?!$site_link)%i", $link)) {
		$link = preg_replace('/rel=\S(?!nofollow)\S*/i', 'rel="nofollow"', $link);
	}
	
	return $link;
}
	
?>