spree_paypal_express/app/controllers/paypal_express_callbacks_controller.rb

class PaypalExpressCallbacksController < Spree::BaseController
  include ActiveMerchant::Billing::Integrations
  skip_before_filter :verify_authenticity_token

  ssl_required

  def notify
    retrieve_details #need to retreive details first to ensure ActiveMerchant gets configured correctly.


    @notification = Paypal::Notification.new(request.raw_post)

    # we only care about eChecks (for now?)
    if @notification.params["payment_type"] == "echeck" && @notification.acknowledge && @payment && @order.total >= @payment.amount
      @payment.started_processing!
      @payment.log_entries.create(:details => @notification.to_yaml)

      case @notification.params["payment_status"]
        when "Denied"
          @payment.fail!

        when "Completed"
          @payment.complete!
      end

    end

    render :nothing => true
  end

  private
    def retrieve_details
      @order = Order.find_by_number(params["invoice"])

      if @order
        @payment = @order.payments.where(:state => "pending", :source_type => "PaypalAccount").try(:first)

        @payment.try(:payment_method).try(:provider) #configures ActiveMerchant
      end
    end

end