Develop a Payment Plugin

I developed the site ([login to view URL]) using Joomla 3. Also I purchased an auction solution and modified the css files. The solution comes with several payment plugin (Paypal, moneybookers, [login to view URL],...) I need to create a custom payment plugin that links the payment to our local bank. I already contacted the local bank and they gave me back all the necessary pdf documentation along with w php sample code. The sample code is a form. I want to create a new payment plugin (will be called AVPC) and install it in the site. The plugin will work ad follows: 1) in the back end, we should have the possibility to enter Merchant ID, Access Code & Secure Hash Secret. 2) Once the user clicks on "Buy Bids" from the bids packages or Click "Purchase" to purchase the winning product; the plugin should send to the local bank payment page the following: Merchant ID, Access Code, Secure Hash Code, Total Amount to be paid, Purchase Reference, Product Description Purchased. 3) On the local bank payment page, the user will enter his credit card info and the bank will do the payment process. 4) Once done, the bank will send us back the result as codes (the result could be payment succeed, not enough balance, credit card expired,...) 5) Based on the result of the payment (meaning based on the response of the bank) the operation is either done successfully or not. I attached the documents received from the bank (pdf & sample php code) + the already existing payment plugins' files that came with the solution.