class ProductInCheckout
  def initialize(product:, quantity: 0)
    @product = product
    @quantity = quantity
  end

  def product_id
    @product.id
  end

  def quantity
    @quantity
  end

  def add_quantity(quantity)
    @quantity += quantity
  end

  def remove_quantity(quantity)
    @quantity = [@quantity - quantity, 0].max
  end

  def total
    (@product.price * quantity) - @product.discount.discount_for_quantity(@quantity)
  end
end