<?php
/*
Plugin Name: KB Linker
Plugin URI: http://adambrown.info/b/widgets/kb-linker/
Description: Looks for user-defined phrases in posts and automatically links them. Example: Link every occurrence of "Wordpress" to wordpress.org.
Author: Adam R. Brown
Version: 1.102
Author URI: http://adambrown.info/
*/

//	OPTIONAL SETTINGS
	/*special characters for foreign languages. Add any you want to the array below. Char goes on left, HTML entity on right. The German codes are here as examples.
		See http://www.w3schools.com/tags/ref_entities.asp for HTML entities.	*/
	$kblinker_special_chars = array(
				'ä' => '&#228;',
				'Ä' => '&#196;',
				'ö' => '&#246;',
				'Ö' => '&#214;',
				'ü' => '&#252;',
				'Ü' => '&#220;',
				'ß' => '&#223;'
	);
	/* 	would you like to add title="" tags to the links with the keyword in them? true or false. */
	define( 'KBLINKER_USE_TITLES' , true );
	/* 	if the preceding setting is TRUE, you can customize the text before or after the keyword below. For example, if you want titles to say "More about KEYWORD.",
		then make before = 'More about ' (note the space) and after = '.' 	*/
	$kblinker_title_text = array(
		'before' => 'More about ', // default: 'More about '
		'after' => ' &raquo;',	// default: '$raquo;' (an arrow pointing to the right)
	);
//	END OF SETTINGS. NO MORE EDITING REQUIRED.


/*	DEVELOPMENT NOTES

	CHANGE LOG
	1.01	initial release
	1.02	quick fix to check is_array before extracting on line 105
	1.03	- added support for German (or other) special characters
		- added support for opening links in different targets
	1.04	add 'i' tag to the tag-detection regexes (it was already in the main replacement one, causing some errors)
	1.05	bugfix
	1.06	bugfix
	1.10	- puts keyword in link's "title" tags
		- won't link the same URL more than once per post, even if multiple keywords are associated with it
		- won't link a page to itself (imperfect)
	1.101	bugfix
	1.102	bugfix

	IMPORTANT NOTE TO ANYBODY CONSIDERING ADDING THIS PLUGIN TO A WP-MU INSTALLATION:
	If you aren't sure whether you are using a WP-MU blog, then you aren't. Trust me. If this warning applies to you, then you will know it.
	For WP-MU administrators: You should not use this plugin. Your users could use it to place (potentially malicious) javascript into their blogs.
	This plugin is PERFECTLY SAFE for non-WP-MU blogs, so ignore this message if you're using regular wordpress (you probably are).

	KNOWN BUGS
	- Pre 1.04: If a tag or attribute contained the keyword, but with different capitalization than specified in options, it was replaced. That causes problems.
	- 1.04: Fixed that bug, but in return, you might find capitalization changing (within tags and attributes) to match that given in the linker's options. Sorry.
	- 1.05 Fixed the capitalization bug

	GENERAL NOTE FOR DEVELOPERS/HACKERS/ETC:
		You will notice that I've included extensive commenting in the code below. I do not have time to support this plugin. The commenting is there to make this plugin
		easy to modify. Please try making modifications on your own before posting a support question at the plugin's URI.
		That being said, you are welcome to post well-informed support questions on my site.

	DATABASE STRUCTURE
		the options->KB Linker page will create a set of matching terms and URLs that gets stored as a list.
		structure of option "kb_linker":
			pairs => array( see below)
			text=>	same content as pairs, but in unprocessed form (for displaying in the option's form)
			plurals => 1, 0		if 1, we should look for variants of the keywords ending in s or es
*/

function kb_linker($content){
	global $kblinker_special_chars,$kblinker_title_text;

	$option = get_option('kb_linker');
	if (is_array($option)){
		extract($option);
	}

	// uncomment for testing (to override options):
	#$pairs = array( 'contributor'=>'http://google.com', 'a'=>'http://yahoo.com/', 'scripting'=>'scripting', 'don'=>'don', 'first post'=>'firstpost.org', 'first'=>'first.org', 'wp'=>'WP.ORG');

	// die if option isn't set yet
	if ( !is_array($pairs) )
		return $content;

	// let's make use of that special chars setting.
	if (is_array($kblinker_special_chars)){
		foreach ($kblinker_special_chars as $char => $code){
			$content = str_replace($code,$char,$content);
		}
	}

	// needed below...
	$usedUrls = array();
	$currentUrl = 'http://' . $_SERVER["HTTP_HOST"] . $_SERVER["REQUEST_URI"]; // may not work on all hosting setups.

	// most of the action is in here.
	foreach ($pairs as $keyword => $url){
		if (in_array( $url, $usedUrls )) // don't link to the same URL more than once
			continue;
		if (strpos( $content, $url )){ // we've already used this URL, or it was manually inserted by author into post
			$usedUrls[] = $url;
			continue;
		}
		if ($url == $currentUrl){ // don't link a page to itself
			$usedUrls[] = $url;
			continue;
		}

		// first, let's check whether we've got a "target" attribute specified.
		if (false!==strpos( $url, ' ' ) ){	// Let's not waste CPU resources unless we see a ' ' in the URL:
			$target = trim(   substr( $url, strpos($url,' ') )   );
			$target = ' target="'.$target.'"';
			$url = substr( $url, 0, strpos($url,' ') );
		}else{
			$target='';
		}
		
		// let's escape any '&' in the URL.
		$url = str_replace( '&amp;', '&', $url ); // this might seem unnecessary, but it prevents the next line from double-escaping the &
		$url = str_replace( '&', '&amp;', $url );
		
		// we don't want to link the keyword if it is already linked.
		// so let's find all instances where the keyword is in a link and precede it with &&&, which will be sufficient to avoid linking it. We use &&&, since WP would pass that
		// to us as &amp;&amp;&amp; (if it occured in a post), so it would never be in the $content on its own.
		// this has two steps. First, look for the keyword as linked text:
		$content = preg_replace( '|(<a[^>]+>)(.*)('.$keyword.')(.*)(</a[^>]*>)|Ui', '$1$2&&&$3$4$5', $content);

		// Next, look for the keyword inside tags. E.g. if they're linking every occurrence of "Google" manually, we don't want to find 
		// <a href="http://google.com"> and change it to <a href="http://<a href="http://www.google.com">.com">
		// More broadly, we don't want them linking anything that might be in a tag. (e.g. linking "strong" would screw up <strong>). 
		// if you get problems with KB linker creating links where it shouldn't, this is the regex you should tinker with, most likely. Here goes:
		$content = preg_replace( '|(<[^>]*)('.$keyword.')(.*>)|Ui', '$1&&&$2$3', $content);

		// I'm sure a true master of regular expressions wouldn't need the previous two steps, and would simply write the replacement expression (below) better. But this works for me.
	
		// set the title attribute:
		if (KBLINKER_USE_TITLES)
			$title = ' title="'.$kblinker_title_text['before'].$keyword.$kblinker_title_text['after'].'"';
		
		// now that we've taken the keyword out of any links it appears in, let's look for the keyword elsewhere.
		if ( 1 != $plurals ){	 // we do basically the same thing whether we're looking for plurals or not. Let's do non-plurals option first:
			$content = preg_replace( '|(?<=[\s>;"\'/])('.$keyword.')(?=[\s<&.,!\'";:\-/])|i', '<a href="'.$url.'" class="kblinker"'.$target.$title.'>$1</a>', $content, 1);	// that "1" at the end limits it to replacing the keyword only once per post.
			/* some notes about that regular expression to make modifying it easier for you if you're new to these things:
			(?<=[\s>;"\'])
				(?<=	marks it as a lookbehind assertion
				to ensure that we are linking only complete words, we want keyword preceded by one of space, tag (>), entity (;) or certain kinds of punctuation (escaped with \ when necessary)
				Note that '&' is NOT one of the allowed lookbehinds (or our '&&&' trick wouldn't work)
			(?=[\s<&.,\'";:\-])
				(?=	marks this as a lookahead assertion
				again, we link only complete words. Must be followed by space, tag (<), entity (&), or certain kinds of punctuation. 
				Note that some of the punctuations are escaped with \
			*/
		}else{	// if they want us to look for plurals too:
			// this regex is almost identical to the non-plurals one, we just add an s? where necessary:
			$content = preg_replace( '|(?<=[\s>;"\'/])('.$keyword.'s?)(?=[\s<&.,!\'";:\-/])|i', '<a href="'.$url.'" class="kblinker"'.$target.$title.'>$1</a>', $content, 1);	// that "1" at the end limits it to replacing once per post.
		}
	}
	// get rid of our '&&&' things.
	$content = str_replace( '&&&', '', $content);
	return $content;
}


function kb_linker_options_page(){
	$sample = 'wordpress->http://wordpress.org/
google->http://www.google.com/ _blank
kb linker->http://adambrown.info/b/widgets/kb-linker/
knuckleheads->http://www.house.gov/';

	if ( $_POST['kb_linker'] ){
		$pairs = str_replace("\r", '', $_POST['kb_linker']);
		$pairs = explode("\n", $pairs);
		foreach( $pairs as $pair ){
			$pair = trim( $pair ); // no leading or trailing spaces. Can mess with the "target" thing in function kb_linker()
			$pair = explode( "->", $pair );
			if ( ( '' != $pair[0] ) && ( '' != $pair[1] ) )
				$new[ $pair[0] ] = $pair[1];
		}
		$pairs = $new;	// contains the pairs as an array for use by the filter
		$text = $_POST['kb_linker'];	// contains the pairs as entered in the form for display below
		
		$plurals = ( 1 == $_POST['kb_plurals'] ) ? 1 : 0;
		$option = array( 'pairs'=>$pairs, 'text'=>$text, 'plurals'=>$plurals );	// store both versions of the option, pairs and text
		update_option( 'kb_linker', $option );
		print '<div id="message" class="updated fade"><p><strong>KB Linker options updated.</strong> <a href="'.get_bloginfo('url').'">View site &raquo;</a></p></div>';
	}else{
		$option = get_option('kb_linker');
		if (is_array($option)){
			extract($option);
		}else{
			$text = $sample;
			$plurals = 0;
		}
	}

	$checked = ( 1 == $plurals ) ? 'checked="checked"' : '' ;

	print '
	<div class="wrap">
	<h2>KB Linker</h2>
	<p>KB Linker will link phrases you specify to sites you specify. For example, you could make it so that whenever "Wordpress" occurs in a post it is automatically linked to wordpress.org.</p>
	<p>Enter your keyword-URL pairs in the box below. Each pair should appear on its own line. Separate each keyword from its respective link with "->". Look at the bottom of this page for important details. Below are a few examples to get you going. Note that the link to Google will open in a new window, since it is followed with "&nbsp;_blank" (note the space).</p>
	<blockquote><pre>'.$sample.'</pre></blockquote>
	<p>Alright, knock yourself out:</p>
	
	<form method="post" action="http://'.$_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'].'">
	<textarea id="kb_linker" name="kb_linker" rows="10" cols="45" class="widefat">'.$text.'</textarea>
	<p><input type="checkbox" '.$checked.' name="kb_plurals" id="kb_plurals" value="1" /> Also link the keyword if it ends in <i>s</i> (i.e. plurals in certain languages)</p>
	<p class="submit" style="width:420px;"><input type="submit" value="Submit &raquo;" /></p>
	</form>
	
	<p>Considerations:</p>
	<ul>
		<li>URLs should be valid (i.e. begin with http://)</li>
		<li>The same URL can appear on more than one line (i.e. with more than one keyword).</li>
		<li>Because a word can only link to one site, a keyword should not appear on more than one line. If it does, only the last instance of the keyword will be matched to its URL.</li>
		<li>If one of your keywords is a substring of the other--e.g. "download wordpress" and "wordpress"--then you should list the shorter one later than the first one.</li>
		<li>Keywords are case-insensitive (e.g. "wordpress" is the same as "WoRdPrEsS").</li>
		<li>Spaces count, so "wordpress" is not the same as "wordpress ".</li>
		<li>Keywords will be linked only if they occur in your post as a word (or phrase), not as a partial word. So if one of your keywords is "a" (for some strange reason), it will be linked only when it occurs as the word "a"--when the letter "a" occurs within a word, it will not be linked.</li>
		<li>You can use any valid target attribute, not just "_blank"--see <a href="http://www.w3schools.com/tags/tag_a.asp">W3C</a> for a list of valid targets.</li>
	</ul>
	</div>
	';
}

function kb_linker_admin_page(){
	add_submenu_page('options-general.php', 'KB Linker', 'KB Linker', 5, 'kb_linker.php', 'kb_linker_options_page');
}

add_filter('the_content', 'kb_linker', 9); // run before Dagon Design Sitemap Generator (runs at priority 10)
add_action('admin_menu', 'kb_linker_admin_page');
?>