so one idea is to fully expand it first and then parse it.

Of course, you need to handle things like

e2e4 and Rad4 and so on.

I am also certain that if the first letter is not upper case then it is a pawn move(i.e. all the other moves must give the name of the piece that is moving)

so you could change e2e4 to Pe2e4 or Pe2Pe4