class Checkout
  class InvalidItem < StandardError; end

  AVAILABLE_ITEMS = {
    PI5: 60.00,
    ZERO2W: 15.00,
    PICO2: 4.00
  }

  def initialize
    @items = []
  end

  def add(item)
    raise InvalidItem unless valid_item?(item)
    @items.push item
  end

  def items
    @items
  end

  def total
    pre_discount_total - current_discount
  end

  private

  def valid_item?(item)
    return AVAILABLE_ITEMS.keys.include?(item)
  end

  def current_discount
    # BOGOF ZERO2W
    discount = (@items.count(:ZERO2W) / 2.0).floor * AVAILABLE_ITEMS[:ZERO2W]


    # TODO: Bulk PICO2

    return discount
  end

  def pre_discount_total
    @items.reduce(0.00) do |running_total, item|
      running_total + AVAILABLE_ITEMS[item]
    end
  end
end