Plugin: Set folder title from Filename start

I have some kind of easy - I think - trouble with Lightroom SDK. I am brand new to this so I figured I need some help.

I am tweaking the FTP Upload plugin that you can find here:
https://github.com/micdah/LrControl/tree/master/Docs/Lightroom%20SDK%206.0/Sample%20Plugins/ftp_upload.lrdevplugin

What I want to achieve is to set the folder title depending on witch filename I choose in the dialog window above.

I want to be able to chose filename: ABCD1234_[sequensenumber 0-99].jpg

Then I want the folder tree on my FTP to be by just adding ABCD1234 in textfield and hit Export:

ABCD1234

- ABCD1234_1.jpg

- ABCD1234_2.jpg

Anyone out the kind enough to help me?

Thanks in advance!