Custom redirect after ordering, depending on product

[nightkingdoms]

OK, kind of a weird thing, but I'm trying to think of how to do this effectively.

 

I'm creating a SAAS (Software As A Service) site and already have all my clients and everything fully invested in WHMCS. What I want to do is:

 

a) customer clicks on link at SAAS site to order the service;

b) customer taken to WHMCS site with service added to cart;

c) customer fills out all the info and makes payment;

d) customer is sent back to SAAS site to create their account.

 

I've looked at the completed order hook but it doesn't provide a way to check which product/service was bought nor any info on whether or not you could redirect someone at that junction anyway. I've thought about editing the completed page template but again, I'm not seeing if you can see which product/service they bought.

 

Ideally I'd like WHMCS to basically act like the payment provider for the SAAS site. WHMCS would handle ordering info, customer info, payment taking, monthly invoices and their payment taking, but the SAAS would handle their actual service.

 

Any ideas? I need a way to check for a completed order, check the product ID to see if it's the SAAS product, then interrupt the process after that to send customer back to SAAS with their order ID.

 

Thanks everybody!