OSCOMMERCE ACCOUNT BALANCE SYSTEM

i want to add a new PAYMENT OPTION in oscommerce called Account Credit Note: this will be a PAYMENT MODULE / METHOD NOT an ORDER TOTAL module!! so they will choose it on the PAYMENT PAGE and if they have enough balance then the order can be confirmed and the order total will be deducted from their Balance e.g customer_account_balance (now) = 25.00 order_total (now) = 18.00 Customer Select Account Credit from the checkout_payment page The system checks to see if their balance can COVER the order total i.e if Balance now => order total then proceed else display error or popup " Sorry you have insufficent balance to cover the order, please remove some items, topup your balance or choose another payment method." Then they can decide what to do BUT the order will NOT be allowed to be CONFIRMED if Balance (now) < Order Total. So if the balance (now) >= order total customer confirms order balance (after) = balance (before) - order_total (before) in this case balance (after) = 25.00 - 18.00 = 7.00 so after the customer confirms their order their balance will be updated in the database to 7.00 next time if they place another order for say 10.00 then they will get a warning cos they are 3.00 short so not rocket science. part 2: we need to have a topup page where they can reload or topup their balance, they can select from a choice of fixed amounts e.g £5 £10 £15... up to £100 and this will be added to their TOPUP BASKET and they can pay for this the same way they pay for a normal order. please note this is not a normal order this is a balance TOPUP so the store manager will not need an email of this. only the customer and web admin but this part is easy to control so the critical part will be makign sure the balance is increased properly after a topup and reduced after an order. Note: there must be at least enough balance to cover the order total this is a PAYMENT OPTION not an order total class oscommerce knowledge needed no time wasters