Parent Page Link Not Working Correct.

On my file manager I am trying to create a parent button link which will go back to previous page.

How ever if i am in a sub folder and lets say on page 3 of pagination my parent button will only display the per page query like so

Code:

http://localhost/project-2-upload/index.php?c=filemanager&per_page=6

It should display like

Code:

http://localhost/project-2-upload/index.php?c=filemanager&image_directory=Hello&per_page=6

I can echo $this->input->get('image_directory') this fine and gets the correct query string.

I am not sure what is wrong with code below any suggestions on improvment / examples and why it might not be working

PHP Code:

$parent_url = '';             

//$thined_image_directory = substr($this->input->get('image_directory'), 0, strrpos($this->input->get('image_directory'),'/'));

if (null !==($this->input->get('per_page'))) {
    $back_page_no = $this->input->get('per_page') - $files_limit;

    $parent_url = '&per_page=' . $back_page_no;
}

if (null !==($this->input->get('image_directory'))) {
    $pos = strrpos($this->input->get('image_directory'), '/');

    if ($pos) {
        $parent_url = '&image_directory=' . urldecode(substr($this->input->get('image_directory'), 0, $pos));
    }
}

$data['parent'] = site_url('c=filemanager')  . $parent_url; 


There's only one rule - please don't tell anyone to go and read the manual.  Sometimes the manual just SUCKS!