在PHP中继续下载链接

The following file (which I don't understand it at all) serves my requested file and makes it ready to be downloaded. But, the links that are created and served by this file miss really important items when downloading by IDM.

File size: (unknown), Time left (unknown) , Resume capability (unknown).

Very unprofessional and bad in all aspects. What should I do as a novice?

if (isset($status) && ($status == 'd')) {  //if Every Thing Is Fine The Download Start 

$filename = $url;
$extension = fileexten($filename);

$fakename = fakefilename($downcode);

$mime = contenttype($extension);

// set_time_limit(0);
if ($notadownload == FALSE) {
    header('Pragma: public');

    header('Expires: 0');

    header("Content-Type:" . $mime);

    header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
    header('Content-Disposition: attachment;filename=' . $fakename . '.' . $extension);

    header("Content-Transfer-Encoding: binary");

    ob_clean();

    flush();

    @readfile($filename);

} else {

    $mime = getContentType($filename);
    header("Content-Type:" . $mime);

    if (strpos($mime, 'text') == FALSE) {
        $extension = fileexten($filename);
        header('Content-Disposition: inline;filename=' . $fakename . '.' . $extension);
    }

    echo @file_get_contents($filename);

}
}