Optionally add free items to cart automatically when condition met

Phew! That was a doozy, but I got it working. Discounts are applied to the product being discounted, which is why there's a lot of hocus pocus in this patch. I am aware of its imperfections but figured I'd contribute something back and see if anyone cared. Let's work together to improve it.

Disclosure: I coded this to work for free item discounts that require one product to be added to the cart and that are applied to specific products (filter_type = FILTER_TYPE_PRODUCTS). I am certain there are lots of use cases it doesn't work properly for, but it works pretty well for mine. It even respects max_times_applied! I've figured out some pretty robust math that makes sure the right amount of free items are added, but it could probably be simplified. It probably doesn't work too well with attributes or anything, but it'll work with base models.

Anyway, I hope this feature can make it into this module or at least inspire something. This module needs a good amount of refactoring, really - tons of code repeat could be avoided. I will try to do so next time I work with it, but in a separate issue.

Patch attached.

Detailed current state of patch.

The previous patch contained an issue with Maximum Applications; it did not respect a setting of 0. Now it should. Patch attached.

Thanks for "blessing" the patch! I hope it gets reviewed and improved too.

Excellent question. With my session var + hook_init trick I can simulate an *after* add to cart hook, which lets me work with a cart already containing data instead of having to fake said data myself. With the discount-retrieving functions available to me, that was easiest.

@jrust: Yeah, the data about is being added to the cart is there, but it is not formatted the same way as it is after add_to_cart as run and you subsequently call uc_cart_get_contents(). I would have to massage it to that format if I wanted to call whichever function I'm calling (get_codeless_discounts or something) and not write a new function. Doing it in hook_add_to_cart, if it can be done in a coherent way, is better in my opinion, but I didn't have the time to go down that path, so I went with a reasonably clean solution that I knew wouldn't introduce strange issues (faking a data structure can never be good).
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OK, I just looked at the patch. I think one big drive was to have all the cart data (especially quantity) in one place. I do some hocus pocus to make sure the right quantity of free items is added, and to do this I need to know both how many of the required_product items are in the cart and how many Free items products are in the cart. This data could be calculated, yeah, but it's easier to work with it when it's already there.

I actually just noticed an issue with my approach. It is possible to stop cart adding in hook_add_to_cart, but my approach always assumes it is successful. A simple before-and-after quantity check could get around that, though. A bit of an edge case, but worth thinking about.

All in all, though, improvements could be made to my patch, and I contributed it knowing that. So if something seems weird, keep asking me as you're doing. It might actually just be kinda weird. The whole thing for me still has a bit of a hackish feel to it, and it's partially because I was working with the module understanding I had and didn't want to write new discount-retrieval functions, but doing so would probably make the code cleaner and more understandable.

Hope this explains.

Well, as mentioned, this only works with the Free items type of discount, and it was built specifically to depend on a required product being set. It wouldn't be that hard to extend, though I don't foresee myself being the one to enhance the patch. One would basically just check the code and make sure the information that the discount-handling function needs is there (e.g. the current order total) and that it is fed the correct data (e.g. things were a bit backwards with required_product, but for total price that wouldn't be necessary). Then the discount-calculation functions in the module itself should be able to take over from there. The code that adds the free items is pretty simple, and as long as it gets the right data, it would also work.

Thanks for the attribution!

hockey2112: The maintainer already committed the functionality in this issue. If the official version of the module is dated before when he said he did that, then download the development version. I didn't see any patches in the other issue queue.

Also: http://drupal.org/patch/apply details the process.

Tweaked text a bit more, removed some extra text.