Script for automating t shirt mockup

Hi guys,

I've read and tried some pretty similar posts from others about this problem but failed, so I created this post and hope that some one can help me out.
I have 3 folders:
- PNG: I saved my designs in PNG format in this folder (let's say I have 500PNG designs in this folder)
- PSD: where I saved PSD mockup files (5PSD mockups)
- JPG: the folder where I will save exported files with JPG format

I need a script that:
- Allows me to choose the design/mockup/export folders (PNG/PSD/JPG in this case).
- Replaces Smart Object layer in each PSD files (in PSD folder) by a PNG file (in PNG folder) then save as a JPG file (to JPG folder).
(in the end I'll have 5PSD x 500PNG ====>>> 2500JPG files in JPG folder)

Any kind of help will be extremely appreciated. Thank you in advance!