Shopping RUs computer store

Description

ShopeOz is starting a computer store. You have been engaged to build the checkout system. We will start with the following products in our catalogue

SKU	Name	Price
ipd	Super iPad	$549.99
mbp	MacBook Pro	$1399.99
atv	Apple TV	$109.50
vga	VGA adapter	$30.00

As we're launching our new computer store, we would like to have a few opening day specials.

We're going to have a 3 for 2 deal on Apple TVs. For example, if you buy 3 Apple TVs, you will pay the price of 2 only
The brand new Super iPad will have a bulk discounted applied, where the price will drop to $499.99 each, if someone buys more than 4
We will bundle in a free VGA adapter free of charge with every MacBook Pro sold

As our Sales manager is quite indecisive, we want the pricing rules to be as flexible as possible as they can change in the future with little notice.

Implementation Details

Services:

Product
Offers
Checkout
Offer Resolution

Logic:

A checkout service input will look like: { atv: 3, vga: 1 } The checkout service queries the product service and creates a detailed map and passes it to offer service.
An offer looks like: { id: 'offerId', productTags: [ 'productA', 'productC' ], OfferFunction : function }
The productTags is an optimization. Not all offers are tried. Only offers which are tagged for the products present in the checkoutMap are tried. Also the entire checkoutMap is sent to the offerFunction because there might be very complicated calculations involved. The offerService returns something like: { offerA : { totalPrice: X, extraOffer: { productFree: { productName: 'productFree', quantity: y, price: Z } } } }

So in the returned map keys are the names of the offers applied. Inside each value, the totalPrice is the new price after application of that offer. extraOffer is to handle cases when a offer is like: you can get productX for free (price will be 0) or you can buy productX for reduced price of Z because of offerA.

Offer resolution service now blindly chooses the first offer.

General

Most of the places maps has been used instead of arrays for optimization.
The src/__tests__/integ.spec.ts has the full test.
The src/offers/ contains the actual offer implementation.

matthew-0x / shopping_cart