I've found where order discount is calculated On cart.php (lines 1525-1551) and on cart_rule.php (line 841-850) For every rule, prestashop calculate % reduction on total order price reading this value from
$order_total = $context->cart->getOrderTotal($use_tax, Cart::ONLY_PRODUCTS, $package_products);
Now i think i need to decrease this value everytime a % reduction is calculated Someone can help me? Thanks Ramio