Add basic Meltdown support

action.php

<?php
/**
 * DokuWiki Plugin markdownextra (Action Component)
 *
 * @license GPL 2 http://www.gnu.org/licenses/gpl-2.0.html
 * @author  Andreas Gohr <andi@splitbrain.org>
 */

// must be run within Dokuwiki
if (!defined('DOKU_INC')) die();
if (!defined('DOKU_PLUGIN')) define('DOKU_PLUGIN',DOKU_INC.'lib/plugins/');
require_once DOKU_PLUGIN.'action.php';

class action_plugin_markdownextra extends DokuWiki_Action_Plugin {

   function register(&$controller) {
      $controller->register_hook('PARSER_WIKITEXT_PREPROCESS',
'BEFORE', $this, 'handle_parser_wikitext_preprocess');
      $controller->register_hook('TPL_METAHEADER_OUTPUT',
'BEFORE', $this, 'handle_meltdown_metadata');
   }

   function handle_parser_wikitext_preprocess(&$event, $param) {
       global $ACT;
       global $ID;
       global $TEXT;
       // Check if file is a .md page:
       if(substr($ID,-3) != '.md') return true;
       // Check for default view (in this case there is only 1 parsed text)
       // or check that the text parsed is the text being edited
       // (see: http://www.dokuwiki.org/devel:environment#text)
       if($ACT != 'show' && $event->data != $TEXT) return true;
       
       if ($this->getConf('frontmatter')){
           if (preg_match('/^---\s*\n(.*?\n?)^---\s*$\n?(.+)/sm',$event->data, $match)){
               $event->data = sprintf("%s<markdown>\n%s\n</markdown>", $match[1], $match[2]);
           }else{
               $event->data = "<markdown>\n".$event->data."\n</markdown>";
           }
       }else{
           $event->data = "<markdown>\n".$event->data."\n</markdown>";
       }
   }

   function handle_meltdown_metadata(&$event, $param) {
       global $ACT;
       global $ID;
       // Check if file is a .md page:
       if(substr($ID,-3) != '.md' || $ACT != 'edit') return;
       
       $event->data['link'][] = array(
            "rel"     => "stylesheet",
            "type"    => "text/css",
            'href'    => 'http://iphands.github.com/Meltdown/dupe/css/meltdown.css');
       $event->data['script'][] = array(
            'type'    => 'text/javascript',
            '_data'   => '',
            'src'     => 'http://iphands.github.com/Meltdown/dupe/js/jquery.meltdown.js');
        $event->data['script'][] = array(
            'type'    => 'text/javascript',
            '_data'   => '',
            'src'     => 'http://iphands.github.com/Meltdown/dupe/js/lib/js-markdown-extra.js');
        $event->data['script'][] = array(
            'type'    => 'text/javascript',
            '_data'   => '',
            'src'     => 'http://iphands.github.com/Meltdown/dupe/js/lib/textinputs_jquery.js');
        $event->data['style'][] = array('type'  => 'text/css',
                                '_data' => '.meltdown_preview { resize: vertical; }'.
                                '.meltdown_wrap textarea { margin-bottom: 5px !important; }');
        $event->data['script'][] = array(
            'type'    => 'text/javascript',
            '_data'   => 'jQuery(document).ready(function($) {'.
                        '$("#tool__bar").hide().after($("<div\>", {text: "[Show original toolbar]", click: function() {$(this).remove();$("#tool__bar").show();}}));'.
                        '$("#wiki__text").meltdown();'.
                        '$(".meltdown_wrap").append($(".meltdown_preview-wrap"));'.
                        '$(".meltdown_control-preview").click();'.
                        '});');
   }
}