/*
plugin name: nofollow reciprocity
plugin uri: http://www.inverudio.com/programs/wordpressblog/nofollowreciprocity.php
description: searches for links to large sites using 'nofollow' tags for external links, and puts the same tag on links to those sites (wikipedia.org, stumbleupon.com, and similar)
author: lazar kovacevic(based on 2 plugins quoted below)
version: 1.0
author uri: http://www.inverudio.com
*/

/* based on:

plugin name: wikipedia nofollow
plugin uri: http://whatjapanthinks.com/wikipedia-nofollow/
description: searches for links to wikipedia.org, and adds a rel="nofollow" tag if necessary
author: ken yasumoto-nicolson (based on identify external links by mark jaquith)
version: 1.0
author uri: http://whatjapanthinks.com

plugin name: identify external links
plugin uri: http://txfx.net/code/wordpress/identify-external-links/
description: searches the text for links outside of the domain of the blog. to these, it adds <strong>class="extlink"</strong> (and optionally, <strong>target="_blank"</strong>).
Author: Mark Jaquith
Version: 1.3
Author URI: http://txfx.net/
*/

/* Copyright 2005 Mark Jaquith (email: mark.gpl@txfx.net)
Additional changes Copyright 2007 Ken Yasumoto-Nicolson (email: seron@whatjapanthinks.com)

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/

function wp_get_domain_name_from_uri($uri){
preg_match("/^(http:\/\/)?([^\/]+)/i", $uri, $matches);
$host = $matches[2];
preg_match("/[^\.\/]+\.[^\.\/]+$/", $host, $matches);
return $matches[0];
}

function wp_has_no_rel_nofollow($text)
{
if ( preg_match("/rel=[\"\'].*?nofollow.*?[\"\']/i", $text ) )
return false;
else
return true;
}

function wp_inarray($needle, $array, $searchKey = false)
{
if ($searchKey) {
foreach ($array as $key => $value)
if (stristr($key, $needle)) {return $key;}
}
else {
foreach ($array as $value)
if (stristr($value, $needle)) {return $value;}
}
return '';
}

function parse_nofollow_reciprocity($matches)
{

//add in next line's array sites that you think do not deserve credit because they don't give it to other sites.
if ( wp_inarray(wp_get_domain_name_from_uri($matches[3]), array("wikipedia.org","del.icio.us","stumbleupon.com","ma.gnolia.com","simply.com","blinklist.com","startaid.com","netvouz.com","facebook.com","shadows.com","yahoo.com","google.com","thisnext.com-removed-due-to-users-feedback","linkter.hu","segnalo.alice.it","addthis.com","youtube.com","blogger.com")) &&
wp_has_no_rel_nofollow( $matches[1] ) &&
wp_has_no_rel_nofollow( $matches[4] ) )
{
return '<a rel="nofollow" href="' . $matches[2] . '//' . $matches[3] . '"' . $matches[1] . $matches[4] . '>' . $matches[5] . '</a>';
}
else
{
// Do nothing
return '<a href="' . $matches[2] . '//' . $matches[3] . '"' . $matches[1] . $matches[4] . '>' . $matches[5] . '</a>';
}
}

function wp_nofollow_reciprocity($text)
{
$pattern = '/<a (.*?)href="[\"\'](.*?)\/\/(.*?)[\"\'](.*?)">(.*?)<\/a>/i';
$text = preg_replace_callback($pattern,'parse_nofollow_reciprocity',$text);
return $text;
}

// filters have high priority to make sure that any markup plugins like Textile or Markdown have already created the HTML links
add_filter('the_content', 'wp_nofollow_reciprocity', 999);
add_filter('the_excerpt', 'wp_nofollow_reciprocity', 999);

// delete this one if you don't want it run on comments
add_filter('comment_text', 'wp_nofollow_reciprocity', 999);