coupon discount improvements

i suggest:

1) limit coupon to one or more products

2) limit coupon to one or more category

3) limit coupon to one or more brands

i know this could be similar to ON Sale...

4) add the option to choose if the coupon applies only to elegible product/s or to all the cart

5) add "free shipping" as discount option

6) creation of x random coupon codes with an option to save them on a file, for example to print each of them on flyers for a "one time" use

The coupon module is intended to make coupons quickly and easily, without needing to enter a lot of parameters.  #1 - #5 can be accomplished with the On Sale module, which is intended for detailed coupons where there are more conditions.  The function is already in the Gahela system, just in a different module.

As for #6, the coupon module already has the ability to have multiple different coupon codes for a single coupon.  I will add an option to generate a group of random coupons to the development list.

if i have understood well, on sale coupon generation needs a previous order made to generate a coupon

On Sale doesn't require a previous order, that is just one of the options to create a coupon.  In each sale there is an option to add a coupon code, and when this coupon field is filled a coupon will be required to activate the sale: