Max quantity for bulk buy implementation is too complicated

[mkllnk]

Description

Reviewing openfoodfoundation/openfoodnetwork#2880 (comment) I noticed that our bulk buy implementation is overly complicated and confusing. The idea of bulk buy is that the shop orders in bulk, which is cheaper. For example 50 kg bags of potatoes have better value (per kg) than 5 kg bags. The big bag gets split up for customers, depending how much they want. Customers order the desired quantity of a product, for example 3 kg of potatoes. But they can also indicate that they would take up to 5 kg of potatoes if it's necessary to make bulk buy work.

In the current code we modified the Spree::LineItem model and added another field called max_quantity. It is optional and can be activated on product level (field group_buy). In order to make this work, we had to override a lot of Spree logic to pass the max_quantity through any stock logic.

Expected Behavior

The implementation is small and easy to understand. It is separate from Spree's logic and behaves like an optional add-on.

Actual Behavior

We modified a lot of Spree logic which makes upgrades difficult.

Steps to Reproduce

Some of the affected code:

• app/controllers/cart_controller.rb
• app/models/spree/line_item_decorator.rb
• app/models/spree/order_decorator.rb
• app/serializers/api/admin/line_item_serializer.rb
• app/serializers/api/line_item_serializer.rb
• app/services/cart_service.rb
• app/views/spree/admin/orders/bulk_management.html.haml
• app/views/spree/products/_add_to_cart_quantity_fields.html.haml
• db/migrate/20120802031147_add_group_buy_fields.rb
• several reports and specs

Context

We are working on the Spree upgrade and decided that we should not include this in the current upgrade. This can be done separately and it shouldn't delay the upgrade. It's tech debt to be paid after the Spree upgrade.

Possible Fix

Implement a new model called QuantityRange which belongs to a LineItem. It would also allow us to set a minimum quantity if that feature is requested.

[kirstenalarsen]

A note that I would expect this to be completely redone when we implement the new network structure as the bulk buy variant will become the base of other combination / split variants. So definitely the way it is done now can be done away with. Could this be a case of a good first implementation of new network structure (alongside the customer prices)? We need to keep this functionality as we have people using it, but it we need to pull out out / redo to enable spree upgrade then we should think through and create the new architecture that we ultimately want? @myriamboure @luisramos0 @sauloperez @HugsDaniel

[luisramos0]

This is not required for the spree upgrade.
anyway, I am looking forward getting into "the network" story :-D

[myriamboure]

Count on us to tell you the story whenever you want @luisramos0 we love telling those kind of stories :-) Agree with you on principle @kirstenalarsen even thought I think we will need to implement first some product chain basic features before we touch this so it might be something that happen a bit later in the process... without the backbone of new product chain not sure we can redo this, but we can think about it ! If not touched by Spree upgrade no hurry :-)