pos.rb

class BulkPrice
  attr_accessor :quantity, :price
  def initialize(quantity, price)
    @quantity = quantity
    @price = price
  end
  def price_per_item
    price / quantity
  end
end

class Pricing
  def initialize(price, bulk_price=nil)
    @price = price
    @bulk_price = bulk_price
  end

  def total(quantity)
    if @bulk_price
      remainder = (quantity % @bulk_price.quantity)
      (@bulk_price.price_per_item * (quantity - remainder) + (@price * remainder))
    else
      @price * quantity
    end
  end
end

class Terminal
  PRODUCT_PRICINGS = {
    "A" => Pricing.new(2.00, BulkPrice.new(4, 7.00)),
    "B" => Pricing.new(12.00),
    "C" => Pricing.new(1.25, BulkPrice.new(6, 6.00)),
    "D" => Pricing.new(0.15)
  }

  def set_pricing(product_pricings)
    @product_pricings = product_pricings
  end

  def scan(product_code)
    quantities[product_code] = (quantities[product_code] || 0 ) + 1
  end

  def total
    total = 0
    quantities.each do |product_code, quantity|
      pricing = @product_pricings[product_code]
      total += pricing.total(quantity)
    end
    total
  end

private

  def quantities
    @quantities ||= {}
  end
end