creation of a simple payment plugin

[smalldragoon]

Hi,
For an old school RPG game ( dice, pen and paper ) , I would like to setup a shop to buy some items.
To do so, I installed a Virtuemart. so far, so good.
as it fake, I can not user real baning data. I created an basic API for the payment in PHP which colelct parameters from POST   myniste.com/API.php?CC=234567&amount=2355&exp_date=012018 .etc..

If all parameters are ok then transaction is validated, otherwise -> KO.

I was looking for a template of a payment plugin  but impossible to find one.
I had a look to the authorize.net which could match pretty well my need I think ( Credit card validation ? )

Workflow is pretty simple

Payment OK -> order status changed to shipping with comment : ok , payment approved
KO -> order stays in pending , comment " paiement refused"

Anyone an idea ? suggestion ?