TextMaster's quest for global domination has prompted us to open a supermarket - we sell only three products:

+--------------|--------------|---------+ | Product Code | Name | Price | +--------------|--------------|---------+ | FR1 | Fruit tea | $3.11 | | AP1 | Apple | $5.00 | | CF1 | Coffee | $11.23 | +--------------|--------------|---------+ 

Our CEO is a big fan of buy-one-get-one-free offers and of fruit tea. He wants us to add a rule to do this.

The COO, though, likes low prices and wants people buying apple to get a price discount for bulk purchases. If you buy 3 or more apple, the price should drop to $4.50. 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 fulfils these requirements in Ruby.

Here are some test data:

Basket: FR1, AP1, FR1, CF1 Total price expected: $22.25 

Basket: FR1, FR1 Total price expected: $3.11 

Basket: AP1, AP1, FR1, AP1 Total price expected: $16.61