$post_content = preg_replace("/\r\n/i", "\n", $post_content);
$post_content = preg_replace("/\n\r/i", "\n", $post_content);
$post_content = preg_replace("/\r/i", "\n", $post_content);
$post_content = preg_replace_callback(
    "/<pre>((?:.|\n)*?)<\/pre>/i",
    create_function(
        '$match',
        'return "[code]" . preg_replace("/ /i", "&nbsp;", preg_replace("/\t/i", "    ", preg_replace("/\n/i", "<br>", $match[0]))) . "[/code]";'
    ),
    $post_content
);
$post_content = preg_replace("/\s+/i", " ", $post_content);
$post_content = preg_replace("/&nbsp;/i", " ", $post_content);
$post_content = preg_replace("/(?!^)(?:\s*<\/?p(?: .*?)?>\s*)+/i", "\n\n", $post_content);
$post_content = preg_replace("/<br(?:\/| .*?)?>/i", "\n", $post_content);
$post_content = preg_replace("/<script(?: .*?)?>(?:.|\n)*?<\/script>/i", "", $post_content);
$post_content = preg_replace("/<a [^>]*?href=\"?([^ \">]+)\"?.*?>((?:.|\n)*?)<\/a>/i", "[url=$1]$2[/url]", $post_content);
$post_content = preg_replace("/<img [^>]*?src=\"?([^ >\"]+)\"?.*?>/i", "[img]$1[/img]", $post_content);
$post_content = preg_replace("/<blockquote>((?:.|\n)*?)<\/blockquote>/i", "[quote]$1[/quote]", $post_content);
$post_content = preg_replace("/<li>((?:.|\n)*?)\s*(?=(?:<\/ul>|<\/ol>|<li>))/i", "[*]$1\n", $post_content);
$post_content = preg_replace("/<ul>((?:.|\n)*?)<\/ul>/i", "[list]$1[/list]", $post_content);
$post_content = preg_replace("/<ol>((?:.|\n)*?)<\/ol>/i", "[list=1]$1[/list]", $post_content);
$post_content = preg_replace("/<(strong|b)>((?:.|\n)*?)<\/\1>/i", "[b]$2[/b]", $post_content);
$post_content = preg_replace("/<(em|i)>((?:.|\n)*?)<\/\1>/i", "[i]$2[/i]", $post_content);
$post_content = preg_replace("/<u>((?:.|\n)*?)<\/u>/i", "[u]$1[/u]", $post_content);
$post_content = preg_replace("/<.*?>/i", "", $post_content);
$post_content = html_entity_decode($post_content);