Apply custom coupon discount code for products in cart

Question

I want to create rule with below requirement:

product A --- no special price ---coupon code can be use

product B --- Special price ---coupon code cannot be used

product A + product B -----no DISCOUNT on product A and DISCOUNT on product B ---- coupon is applied to product A ONLY

Please give some hint.

Thanks

Answer 1

app\code\core\Mage\Sales\Model\Quote\Address\Total

Discount.php in

  $items = $address->getAllItems();   

you can get all item and

 foreach ($items as $item) {     

in loop you can check your product condition

after that you can rewrite this model for Discount.php in your extension