php给网址替换成链接 正则

因为内容里可能已经带链接的html
所以需要先将链接的代码暂时隐藏，最后再恢复。

 public static function text2link($str='')
    {
        if ($str == '' || !preg_match('/(http|ftp|www\.|@)/i', $str)) {
            return $str;
        }
        $lines = explode("\n", $str . "\n");
        $link = "";
        foreach ($lines as $tt => $vv) {
            $vv = preg_replace("/([ \r\n\t]|^)www\./i", "\\1http://www.", $vv); //www开头自动加http://
            //将现有的链接代码隐藏
            $vv = preg_replace_callback("/href=[\"|']((http|https|ftp):\/\/[^ \r\n]+)[\"|']/i", function ($matches) {
                return "href=\"[link:". base64_encode($matches[1]) ."]\"";
            }, $vv);
            $vv = preg_replace("/((http|https|ftp):\/\/[^ \r\n]+)/i", "<a href=\"\\1\" target='_blank'>\\1</a>", $vv);
//            $vv = preg_replace("/([-a-z0-9_]+(\.[_a-z0-9-]+)*@([a-z0-9-]+(\.[a-z0-9-]+)+))/i", "<a href=\"mailto:\\1\">\\1</a>", $vv);
            //链接代码恢复
            $vv = preg_replace_callback("/\[link:([^\]]+)\]/i", function ($matches) {
                return base64_decode($matches[1]);
            }, $vv);
            $link .= $vv . "\n";
        }
        return $link;
    }