Create sequential code in range based on value in neighboring column

I have a worksheet with two columns:

Column A - Project Name
Column B - Project Code

I need to write a script that populates Column B with a sequential project code IF the project name in Column A contains the characters 'NDA-' at the start.

The sequential code should be 'NDA-001', 'NDA-002', etc. For example:

Column A Column B
Project 1 -
Project 2 -
NDA-Project 3 NDA-0001
Project 4 -
NDA-Project 5 NDA-0002

Any help on this would be greatly appreciated

Thank you,