Cart model

gistfile1.rb

class Cart
  def initialize
    @products = []
    @rules = []
  end

  def regular_total
    @products.map { |p| p.price }.inject(&:+)
  end

  def benefits
    @rules.map { |rule| rule.apply_for(@products) }.inject(&:+)
  end

  def total
    regular_total - benefits
  end

  def <<(product)
    @products << product
  end

  def when_buying(product)
    rule = Rule.new(product)
    @rules << rule
    rule
  end
end