Hello Cabify team, this is my solution for the rubyChallenge, the architecture was designed with an OPP approach so that new functionalities can be easily added. Below some notes explaining what does each class, how they interact with each other and some additional considerations.

Product class allows create individual instances with the attributes code, name and price, all the the info necessary to add a new product to the Store class.

This class groups instances of Product class, with two private methods, add_product method that receives code, name and price like parameters and load_products method, to create all products inside the Store instance. For a future improve, load_products method could receive a external file like a data base to load a big quantity of products.

Instances of OrderItem class contain the following attributes: code to identify the product associated, it's a reader attribute that can't change after created, and quantity, unit_price and discount like attributes accessor , which change according to the number of scanned products and discounts available.

Order class stores instances of OrderItem in the items variable, through the add_item method, each item has an attribute quantity to accumulate the same kind of products, this design facilitates later calculations in Checkout.

This class allows instantiate all available rules at the same time with the load_rules method (for future improvements, these rules could come from an external file to load a large number of rules). It also has the apply_rules method that receives a hash of items to apply the available rules.

Currently there are two rules, both receives a code attribute to relate the instance with the product, and each rule has the apply method that is different depending on the rule. Following this pattern is pretty easy add future rules.

These are the available rules:

• BuyTwoGetOneFreeRule: This rule apply a discount equivalent to one free by each two units.
• BulkPurchasesRule: In addition to the code this rule receives quantity and discount_rate, that allows apply a bulk discount, where by each X units(quantity) receives a Y% (discont_rate) of discount on the unit_price.

This is the Main Class to interact with the app, a new Checkout instance receive pricing_rules like parameter that contents all the discount available rules. Also has two main methods, the first one is scan, that allows register a new product in in the order, the second one is total to get the total to pay on your order, also the class allows call two instance variables , store to know the available products and order to check the items scanned.

Each class is tested with unit tests using Rspec like testing framework, to run the tests, first remember install the gem from your terminal with gem install rspec, then from Project's root run rspec spec to run all the tests at same time, or rspec spec/name_class_spec.rb to run a specific test.

To interact with the app, run ruby co_cli.rb.