I've always done it FIFO.  I think that's required somewhere but can't put my finger on a cite right now.  So start at T-30 days and apply per-share adjustments forward until you either run out of sold shares, run out of acquired shares, or pass T+30.  With my Googlers this often leads to a chain of adjustments that may or may not clear out by year-end.  Also remember the holding period gets adjusted for washed shares which could turn something that looks like short-term into long-term because of the basis adjustment.

The key to surviving this mess is focus on everything per share.

Rick

Edit: Edited to add T+30 expiration.