How to Create credit memo for draft invoices based on events ?

Hi,

I have a requirement to create credit memo for invoices that are based on event PROGRAMATICALLY.  Here is what I am doing

Create event

Generate Draft Invoice

Transfer Invoice

Import Invoice

Tie back invoice.

Now for credit memo,  there is a button on the draft invoice to create it ( write -off) .  When you click on that and enter amount it will create a draft invoice and when you transfer it, it will transferred as credi memo to AR.

I want to do the same thing programatically. I tried to create events of event type "Invoice Adjustment " and "Manual"  with -ve invoice amount.