Supplier Purchase Limit (Credit Limit)

All our suppliers work on a 30 day account, with each we have a specific credit limit. The feature I would like is for each supplier to have a field specifically for having a credit limit value and credit available.

The available field would take into account the total amount of outstanding purchase orders have been raised for that supplier. When raising a new purchase order, the system should disallow/warn when the order value is higher than the remaining credit.

Once PO's are received and marked as paid, the remaining credit value should adjust accordingly.