PaypalExpressHelper#get_purchase_params

paypal_express_helper.rb

module PaypalExpressHelper
  # ... other methods were implemented in the previous blog posts

  def get_totals(cart)
    # implemented in the previous blog posts
  end

  def to_cents(total)
    # implemented in the previous blog posts
  end 

  def get_items(cart)
    # implemented in the previous blog posts
  end

  def get_purchase_params(cart, request, params)
    subtotal, shipping, total = get_totals(cart)
    return to_cents(total), {
      :ip => request.remote_ip,
      :token => params[:token],
      :payer_id => params[:payer_id],
      :subtotal => to_cents(subtotal),
      :shipping => to_cents(shipping),
      :handling => 0,
      :tax =>      0,
      :items =>    get_items(cart),
    }
  end
end