What Function Adds All The Store Details To Cart In The Stores & Pickup Points Addon?

Hi, so I know that when configured correctly, a customer can select a certain store/pickup point at checkout and that it changes the data in the cart, specifically the 'chosen_shipping' array in $cart['product_groups']. The addon adds the store_location_id and store_data of the selected pickup point.

I want to know how it does that, are there specific hooks and core functions that I should be looking at?

I already know that for normal shipping methods, the system just runs fn_checkout_update_shipping($cart, $shipping_ids) and then runs fn_calculate_cart_content() to add the newly selected shipping ids as the 'chosen_shipping' in $cart['product_groups']. Is there a hook somewhere in fn_calculate_cart_content() that inputs the other store details?

Any help would be greatly appreciated, thanks.