Checkout

Technical Evaluation

Assignment

You are the lead programmer for a small chain of supermarkets. You are required to make a simple cashier function that adds products to a cart and displays the total price. You have the following test products registered:

Product code	Name	Price
GR1	Green tea	£3.11
SR1	Strawberries	£5.00
CF1	Coffee	£11.23

Special conditions:

• The CEO is a big fan of buy-one-get-one-free offers and of green tea. He wants us to add a rule to do this.
• The COO, though, likes low prices and wants people buying strawberries to get a price discount for bulk purchases. If you buy 3 or more strawberries, the price should drop to £4.50
• The CTO is a coffee addict. If you buy 3 or more coffees, the price of all coffees should drop to two thirds of the original price.

Our check-out can scan items in any order, and because the CEO and COO change their minds often, it needs to be flexible regarding our pricing rules.

The interface to our checkout looks like this (shown in ruby):

co = Checkout.new(pricing_rules)
co.scan(item)
co.scan(item)
price = co.total

Implement a checkout system that fulfills these requirements.

Test data:

Basket: GR1,SR1,GR1,GR1,CF1 Total price expected: £22.45

Basket: GR1,GR1 Total price expected: £3.11

Basket: SR1,SR1,GR1,SR1 Total price expected: £16.61

Basket: GR1,CF1,SR1,CF1,CF1 Total price expected: £30.57

Running Instructions

Be sure to have Elixir and Erlang installed. Then run:

$ iex -S mix
iex(1)> pr = %PricingRules{
            discount_type: :buy_n_get_x_free,
            threshold: 2,
            operand: 1,
            product_codes: ["GR1"]
            }
iex(2)> pid = Checkout.new(pr)
iex(3)> Checkout.scan(pid, "GR1")
iex(4)> Checkout.scan(pid, "GR1")
iex(5)> Checkout.total(pid)