Question regarding payment processing workflow

We have 3 states:
- Pending
- Processing
- Comleted

Pending, when user chose a payment method and was redirected to "payment gateway/bank gateway", but we dont have yet informations regarding the payment from the provider "paypal" for example order_balance > 0

Processing, user paid for his order, we got informations from our provider and order_balance = 0,
In that state the change between "Pending and Processing" should be automatic,

Completed, user already paid, and shop have sent the package
in this state admin changes manually from processing to completed

And the question is how we can make the change bettween "pending and processing" to be automatic based on the fact that order_balance = 0 trough Rules ?:( me and my friend are getting so lost in there!

here is what we have so far: http://pastebin.com/6MZjYqtu

Posted: Mar 7, 2012