Filenames are numerical code- need last four #'s to be the first four #'s

Question

How do I switch the .jpg of numbers to the beginning of filenames?
I have several hundred files whose filenames have three sets of numbers separated by underscores.
Unfortunately, the last four numbers need to be placed at the beginning of the filenames. This is to establish chronology.
The current number sequence is: site number, date, number of the jpg
The desired number sequence is: jpg number, site number, date.
".jpg" would still be the last entry.
Thanks for any help!

Answer 1

This might help:
var theFolder = Folder.selectDialog("select the folder containing the images to be renamed");
if (theFolder) {
   var theFiles = theFolder.getFiles();
   for (var m = 0; m < theFiles.length; m++) {
      var theName = theFiles[m].name;
      var theLastNumbers = theName.slice( theName.lastIndexOf("_") + 1, -4);
      var theRest = theName.slice(0, theName.lastIndexOf("_"));
      theFiles[m].rename(theLastNumbers + "_" + theRest + ".jpg")
else {
   alert ("no selection")
use it at Your own risk
Edit: Actually it should include some function to ascertain that the files are indeed jpgs or at least retain the original suffix.
Still if the folder contains only jpgs it should work.