求将HTML代码变换为UBB代码的c#正则表达式

public string ubbtohtml(string content)  //ubb转html    {        content = Regex.Replace(content, @"\r\n", "<br/>");        content = Regex.Replace(content, " ", "&nbsp;");        content = Regex.Replace(content, @"\[b\](.+?)\[/b\]", "<b>$1</b>");        content = Regex.Replace(content, @"\[i\](.+?)\[/i\]", "<i>$1</i>");        content = Regex.Replace(content, @"\[u\](.+?)\[/u\]", "<u>$1</u>");        content = Regex.Replace(content, @"\[p\](.+?)\[/p\]", "<p class='load'>$1</p>");        content = Regex.Replace(content, @"\[align=left\](.+?)\[/align\]", "<align='left'>$1</align>");        content = Regex.Replace(content, @"\[align=center\](.+?)\[/align\]", "<align='center'>$1</align>");        content = Regex.Replace(content, @"\[align=right\](.+?)\[/align\]", "<align='right'>$1</align>");        content = Regex.Replace(content, @"\[url=(?<url>.+?)]\[/url]", "<a href='${url}' target=_blank>${url}</a>");        content = Regex.Replace(content, @"\[url=(?<url>.+?)](?<name>.+?)\[/url]", "<a href='${url}' target=_blank>${name}</a>");        content = Regex.Replace(content, @"\[quote](?<text>.+?)\[/quote]", "<div class=quote>${text}</div>");        content = Regex.Replace(content, @"\[img](?<img>.+?)\[/img]", "<img src='${img}' alt=''/>");        content = content.Replace("[face1]", "<img src='../Images/emotion/1.png' style='width:14px; height:14px;' alt='' />");        content = content.Replace("[face2]", "<img src='../Images/emotion/2.png' style='width:14px; height:14px;' alt='' />");        content = content.Replace("[face3]", "<img src='../Images/emotion/3.png' style='width:14px; height:14px;' alt='' />");        content = content.Replace("[face4]", "<img src='../Images/emotion/4.png' style='width:14px; height:14px;' alt='' />");        content = content.Replace("[face5]", "<img src='../Images/emotion/5.png' style='width:14px; height:14px;' alt='' />");        content = content.Replace("[face6]", "<img src='../Images/emotion/6.png' style='width:14px; height:14px;' alt='' />");        content = content.Replace("[face7]", "<img src='../Images/emotion/7.png' style='width:14px; height:14px;' alt='' />");        content = content.Replace("[face8]", "<img src='../Images/emotion/8.png' style='width:14px; height:14px;' alt='' />");        content = content.Replace("[face9]", "<img src='../Images/emotion/9.png' style='width:14px; height:14px;' alt='' />");        return content;    }