Get original URL of page that is being edited

Permalink
Hi all,

here is my issue. I would like to be able to get the original URL of the page that is currently edited.
An editor puts a page in edit mode and then he adds either a content block or a file block and uploads a file through the file manager. I would like to create an automatic notification function (triggered by on_file_add) that informs about the original URL (not the dynamic one in edit mode) of the page where the file was added. I tried:

$myPage = Page::getCurrentPage();
$nh = Loader::helper('navigation');
$myURL = $nh->getCollectionURL($myPage);

but I get an empty string in $myURL.

So my questions would be:
1. Is there a way to get the original URL of a page that is currently in edit mode?
2. Is the URL also accessible when in edit mode the File Manager is launched?

Thanks in advance

Nomoreglitches