Live BBCode Preview

// ABBC Live Compiler for http://dis.4chan.org/
// by Tablecat <http://tablecat.co.cc>

var init = function() {
    var forms = document.forms;
    for (var i = 0; i < forms.length; i++) {
        if (forms[i].action === 'http://dis.4chan.org/derefer') continue;
        var preview = document.createElement('div');
        preview.className = 'preview';
        preview.style.display = 'none';
        forms[i].appendChild(preview);
        var textarea = forms[i].getElementsByTagName('textarea')[0];
        textarea.onchange = textarea.onkeyup = function() {
            var comment = this.value;
            var thread = this.parentNode.parentNode.parentNode.parentNode.parentNode.id.value;
            var script = window.location.href.replace(/^http:\/\/dis\.4chan\.org\/([^\.]+)/, '$1');
            comment = markup(clean_string(comment), thread, script)[0];
            this.parentNode.parentNode.parentNode.parentNode.parentNode.lastChild.style.display = comment ? 'inline-block' : 'none';
            this.parentNode.parentNode.parentNode.parentNode.parentNode.lastChild.innerHTML = comment;
        }
    }
};

var clean_string = function(str) {
    str = str.replace(/[\x00-\x08\x0B-\x1F\x7F]/g, "");
    str = str.replace(/^(\n|\x20)+|[\s]+$/g, "");
    str = str.replace(/&/g, "&amp;");
    str = str.replace(/</g, "&lt;");
    str = str.replace(/>/g, "&gt;");
    str = str.replace(/\"/g, "&quot;");
    return str;
};

var markup = function(str, thread, script) {
    var tagList = [ "#" , "code" , "b" , "i" , "o" , "u" , "s" , "aa" , "m" , "spoiler" , "sup" , "sub" ];
    var malformed = 0;
    var quoteRe = /&gt;&gt;([0-9\-\,l]+)/g;
    str = str.replace(quoteRe, '<a href="read/'+script+thread+'/$1">&gt;&gt;$1</a>');
    // super tags
    for (var i = 0; i < tagList.length; i++) {
        var tag = tagList[i],
        re = new RegExp("(^|[\\s\\S]*?)\\["+tag+"\\]([\\s\\S]*?)\\[\\/"+tag+"\\]($|[\\s\\S]*)", "g");
        while ( str.match(re) ) {
            if (tag === "#")
                str = str.replace(re, "$1"+escape_tag(RegExp.$2)+"$3");
            else if (tag === "code")
                str = str.replace(re, "$1<code>"+escape_tag(RegExp.$2)+"</code>$3");
            else
                break;
        }
    }
    // quote
    var pattern = new RegExp("(\\n|^)&gt; (.*?)(\\n|$)", "g");
    while ( str.match(pattern) )
        str = str.replace(pattern, "$1<span class=\"quote\">$2</span>$3");
    // regular tags
    for (var i = 0; i < tagList.length; i++) {
        var tag = tagList[i],
            re = new RegExp("(^|[\\s\\S]*)\\["+tag+"\\]([\\s\\S]*?)\\[/"+tag+"\\]($|[\\s\\S]*)", "g");
        while ( str.match(re) ) {
            var before = str.replace(re, "$1"),
            content = str.replace(re, "$2"),
            after = str.replace(re, "$3");
            if (fail_check(content, tagList)) {
                str = before + "\x1FB"+tag+"\x1FC" + escape_tag(content) + "\x1FB/"+tag+"\x1FC" + after;
                malformed++;
            }
            else if (tag.match("^(b|i|s|u|sup|sub)$"))
                str = before + '<' + tag + '>' + content + '</' + tag + '>' + after;
            else if (tag === "m")
                str = before + '<tt>' + content + '</tt>' + after;
            else if (tag === "rem")
                str = before + after;
            else if (tag.match("^(spoiler|aa|o)$"))
                str = before + '<span class="' + tag + '">' + content + '</span>' + after;
            else
                break;
        }
    }
    str = str.replace(/\n/g, "<br>");
    str = '<blockquote style="border:1px dashed #000;padding:0.5em;background:#EFEFEF">'+str+'</blockquote>';
    //if (malformed > 0) str += '<div style="color:red"><b>Warning: Malformed markup, '+malformed+' error(s)</b></div>';
    return [unescape_tag(str), malformed];
};

var escape_tag = function(str) {
    str = str.replace(/&gt;/g, "\x1FA");
    str = str.replace(/\[/g, "\x1FB");
    str = str.replace(/\]/g, "\x1FC");
    return str;
};

var unescape_tag = function(str) {
    str = str.replace(/\x1FA/g, "&gt;");
    str = str.replace(/\x1FB/g, "[");
    str = str.replace(/\x1FC/g, "]");
    return str;
};

var fail_check = function(str, tagList) {
    for (var i = 0; i < tagList.length; i++) {
        var tag = tagList[i],
            reup = new RegExp("(.*)\\["+tag+"\\](.*)","g"),
            redwn = new RegExp("(.*)\\[/"+tag+"\\](.*)","g"),
            count = 0;
        while ( str.match(reup) ) {
            str = str.replace(reup, "$1$2");
            count++;
        }
        while ( str.match(redwn) ) {
            str = str.replace(redwn, "$1$2");
            count--;
        }
        if (count !== 0) return true;
    }
    return false;
};

if (window.location.href.search('^http://dis.4chan.org/[^\.]+') != -1) {
    window.onload = function() { init(); };
}