sort by date modified?

[vk7krj]

I would really appreciate some help with a php script to change the way it orders some small images in a directory.
As part of my ham radio hobby I have 4 web pages displaying slow scan tv pictures as infinitely scrolling web galleries. Until very recently they worked fine, ordering the images according to their names, which are also the date & time of reception.
However, a change forced on me by the software I use to receive these has messed the system up by changing the structure of the file names. 
To save having to rename some 30,000 images, I now need to sort them by the last modified date, but try as I might, I can't seem to get it to work. This is my existing php script-

<?php
     $dir = "40mArchives/";    
     if(is_dir($dir)){
        if($dd = opendir($dir)){
            while (($f = readdir($dd)) !== false)
                if($f != "." && $f != "..")
                    $files[] = $f;
            closedir($dd);
        } 
// sensible sort
$sortbool = rsort($files,SORT_STRING);     
 
    $n = $_GET["n"];
    $response = "";
        for($i = $n; $i<$n+12; $i++){
           $response = $response.$files[$i%count($files)].';';
        }
        echo $response;
    }
?>

Which has been working well for quite a number of years- despite the fact I think the sort is not quite right- but it seemed like a good idea at the time!
I have tried all manner of different things from web searches over the last month or so, none of which I have been able to persuade to do what I need.
It doesn't help that as I am aging I am finding it more & more difficult to wrap my brain around these things- so any assistance would be very well received!

This is one of my sstv pages-
https://sstv.vk7krj.com/40m.html
and my main web site-
https://vk7krj.com/

Thanks, Ken, vk7krj

[Barand]

See

 

[vk7krj]

Barand, thanks for taking the time to reply to my question- but after spending yet more hours trying to get this working I am giving up on this solution for now, and having a look at using python to fix the problem instead. I am not a programmer or web developer, just a retired ham trying to make things work the way I want them to. 

I think I can get the errant program to save the files in one directory, then use a python script to rename and move them to the correct directory. Again, I'm no python programmer, but with lots of reading I can usually muddle through. There's quite a bit of python behind my web pages, all of which I wrote myself, and the whole shebang is hosted right here in my radio shack. And like you, I am 75 years young! (and originally from Sheffield, but that was over 50 years ago)

Ken, vk7krj

https://vk7krj.com/index.html

Edited March 30 by vk7krj