Discount coupon functionality in Drupal

I need a drupal expert. Make sure you are expert. You should be available for 8-10 hours/day. I need few customization done in drupal website. Please don't ask for advance payment. I want a form in the backend of drupal to set discount code form. The form should generate a quantity of codes to use with the amount of money OR the percentage off for memberships when they subscribe So for example: A member loggs in and clicks on subscription product checkout. They need to see the discount code textbox on the checkout form Ovbiously all the functionality behind is just to take the percentage off from the product ammount Let me know if u have another approach to this feature Only Drupal Experts Please.