This is a prototype checkout system for a job application at notonthehighstreet.com programming test, according to the following description:

notonthehighstreet.com is an online marketplace, here is a sample of some of the products available on our site:

Product code  | Name                   | Price
----------------------------------------------------------
001           | Travel Card Holder     | £9.25
002           | Personalised cufflinks | £45.00
003           | Kids T-shirt           | £19.95

Our marketing team want to offer promotions as an incentive for our customers to purchase these items.

If you spend over £60, then you get 10% off your purchase If you buy 2 or more travel card holders then the price drops to £8.50.

Our check-out can scan items in any order, and because our promotions will change, it needs to be flexible regarding our promotional rules.

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

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

Implement a checkout system that fulfills these requirements.

Test data
---------
Basket: 001,002,003
Total price expected: £66.78

Basket: 001,003,001
Total price expected: £36.95

Basket: 001,002,001,003
Total price expected: £73.76

In order to instantiate a new product create a new Item object:

Item.new("001", "Travel Card Holder", 9.25)

The item is automatically added to a Class Variable (Hash) that represents the store product catalog. Items can be removed from this hash by invoking the “delete” method from the instantiated object.

Special rules (i.e. discounts) to be applied in the total price calculation can be created using the PromotionalRule constructor method. This method accepts a string with the name of the rule and a block of code, as the following example:

# If you spend over £60, then you get 10% of your purchase
PromotionalRule.new( "10% discount on buys over 60£" ) do
    if @total > 60.0
      @discount = @total * 0.10
    end
end

Important notes! Programmers must define promotional rules taking in mind that the final total price is obtained by:

@total = 0
@basket.each do |item, quant|
    @total += @price[item] * quant # quant == @basket[item]
end
@total -= @discount

Programmers must also have into account the following assumptions:

• The block of code will be executed in the context of a Checkout instance, so it must only use variables and methods that can be accessed by that object;

• The rules are executed in the same order as they are passed to the Checkout object and each rule affects the results for the next rules, so order of execution must be taken into consideration;

• The current total price can be accessed through the variable @total but, since this variable is updated after each rule being executed, any change to @total is irrelevant.