Integration between Drupal Commerce and BillysBilling

In discimport.dk we are using Drupal Commerce Kickstart and we just recently started using BillysBilling.dk as our accounting solution. Therefore we just started to code on a Drupal integration between the two systems in a dedicated module on drupal.org.

If you want any say in how the module evolves, you are more than welcome to come to the issue queue and express your opinion. I am using the official php-sdk for BIllysBilling, which is available from github.com.

Right now we are thinking about two different integrations:

• Rules - create custom actions and events which could pass the objects to the api. I would then need to impleent hook_rules_event_info() and hook_rules_action_info().
• Implement a hook_post_save() which responds to checkout complete or order save - or maybe even better make a new status on an order after executed, namely invoiced.

What would you do?