prestashop 1.6 how i can calculate shipping cost grouping products by supplier?

[reyngod]

I need that when a client makes an order from several suppliers, the shipping costs of each supplier add up.

Example: an order for a product that weighs 1kg from the supplier Biedma Ferreteria (BF ..) charges a cost of 4.84 If the order is for a barbecue that weighs 30kg, it charges you 16.94 If the two products are from the same supplier you do not have to do anything, the price is calculated by prestashop according to the total weight that are 30 + 1 = 31kg But if they are 2 suppliers, the total size would be 4.84 + 16.94 As if it were two different orders

I have been modifying the file (classes / cart.php) and the functions (getPackageShippingCost, getTotalWeight). But I have not had any results so I left it as it was, what functions do I have to modify?, am I wrong in modifying these functions?