jQuery ajax php rename part of a file name

In the frontend i offer the user to rename any of his images. This is done via javascript prompt to get the new name, jQuery ajax and php. When file is renamed it must take effect on 2 files as you see in the links below. 1 in the url is dynamic. It's开发者_JAVA百科 the user id. The thing is i only want to replace the product in the filename and not the _1317804260 that comes after it. In the second link we have thumb_ in front of the file name. So again we only want to replace the product with the new rename. Working on this, it Seems like i need to use explode() many times to get the job done. Is there an easier way to do this.

http://domain.com/userfiles/1/images/product_1317804260.gif
http://domain.com/userfiles/1/images/thumbnails/thumb_product_1317804260.gif

So basically if a new name is newname the final output of the file should be

newname_1317804260.gif
thumb_newname_1317804260.gif

$oldName = "http://domain...product_userid.gif";

$newName = "what the user entered";

$parts = explode('/', $oldName);
$user_path = $parts[3] . '/' . $parts[4]; // it will contain userfiles/1

$parts = explode("_", $oldName);

$product_name = $new_name . "_" . end($parts);
$thumb_name   = "thumb_" . $product_name;

JS:

var tmpName = "product_1317804260.gif".split("_")
var newName = "newname" + "_" + tmpName[1]

PHP:

$tmpName = explode("_", "product_1317804260.gif");
$newName = "newname" . "_" . $tmpName[1];