[ic] custom payment module

[Glenn McCalley]

Here's the situation:

We've got several stores running Interchange V5.2.0  It does the job!  Been 
using it for years.

A new client (big one, of course) wants us to process the charges for their 
store through their own credit card system that they already use for 
contributions.  They also want us to pass order item detail to them in an 
XML type structure so they can maintain their own merged database when 
people have both made a contribution and a store purchase.  The sequence 
would be
- we take the order using the IC checkout page
-- send the charge/item info to our client
-- get their response on the charge
- we show the customer receipt.

They have provided a Perl routine that works, meaning I can run it from the 
command line with a $1.00 amount and the charge gets processed by them OK.

SO!
How do you turn this into a payment module?  I've perused the Payment.pm and 
Payment module directory and am having trouble seeing how they interact, how 
it gets called, where the "OK" or "refused" is returned to the checkout 
process, etc.  It looks like things get mapped/translated into things which 
get mapped/translated into other things where they get mapped once again, 
and somehow somewhere an "OK" signal is returned.  Is there a HowTo or a 
reference on this somewhere?

Thanks!
Glenn.