module CartHelper
    
  def get_cart_info
    # retrieve cart info from session
    cart = session[:cart] 
    item_on_cart = session[:item_on_cart]
    return cart, item_on_cart
  end  
  
  
  # save the cart info into session
  def save_cart_info (cart, item_on_cart)
    session[:cart] = cart 
    session[:item_on_cart] = item_on_cart
  end  
  
  
  # clear the current shopping cart
  def clear_cart
  
    # TODO: Clear the current cart by remove its information 
    # from the session
    
  end
  
  
  
  # add a new product to cart
  def add_product_to_cart (product_id)
    
    # retrieve cart info from session
    cart, item_on_cart = get_cart_info 
    
    if item_on_cart.nil?
      item_on_cart = 0
    end 
    if cart.nil?
      cart = Hash.new(0)
    end 
    
    # get the quatity of the product
    quatity = cart[product_id.to_s];
    if quatity.nil?
      cart[product_id] = 1;
    else
      cart[product_id] = quatity + 1;
    end  
    item_on_cart = item_on_cart + 1
    
    # write back to session
    save_cart_info cart, item_on_cart
  end
  
  
  
  
  # remove a product from the cart
  def remove_product_from_cart (product_id)
  
    # TODO: Remove a product from the shopping cart
    # after removing the product, don't forget to update the
    # item_on_cart information
    # Hints: Hash.delete is a function to remove a key from
    #       a hash object
  end
  
  
end