app/models/cart.rb

   1 class Cart
   2   attr_reader :items
   3
   4   def initialize
   5     @items = []
   6   end
   7
   8   def add_product(product)
   9     current_item = @items.find {|item| item.product == product}
  10     if current_item
  11       current_item.increment_quantity
  12     else
  13       current_item = CartItem.new(product)
  14       @items << current_item
  15     end
  16     current_item
  17   end
  18
  19   def total_price
  20     @items.sum {|item| item.price}
  21   end
  22
  23 end