Make Paypal PDF invoices with Payday

A lot of small web applications use Paypal as their primary gateway for accepting payments. Paypal takes care of the payment transactions for your application and sends the customer back to your site once the payment done. The only thing Paypal doesn’t do is proper invoicing. It sends confirmation emails with the transaction details but many corporate customers require a well-formatted PDF invoice as a proof or purchase.

Payday is a Ruby gem that will help you create simple invoices. It’s a generic PDF invoicing library and as I will show you in this tutorial, it can be easily used to help you create invoices from Paypal transactions.

First thing to do, add the gem to your Gemfile :

gem "payday"

Next, you can create a rails initializer file with your company infos :

# /config/initializers/payday.rb
Payday::Config.default.invoice_logo = "#{Rails.root}/public/images/logo.png"
Payday::Config.default.company_name = "My Company inc."
Payday::Config.default.company_details = "100 Sunset Blvd\nHollywood\nUnited States\ninfo@mycompany.com"

When a client makes a purchase on Paypal, you can configure your account to receive Instant Payment Notifications (IPN). I save each transaction in a Payment model and dump the paypal IPN request params in a serialized hash called paypal_params. This is the method from my model class I use to generate the invoice :

# app/models/payment.rb
serialize :paypal_params

def generate_pdf_invoice
  invoice = Payday::Invoice.new(
    :invoice_number => paypal_params['invoice'],
    :currency => paypal_params['mc_currency'])
  invoice.paid_at = invoice.due_at = created_at.to_date
  invoice.bill_to = invoice.ship_to = paypal_params.slice(
    'address_name', 'address_street', 'address_city',
    'address_zip', 'address_country').values.join("\n")
  invoice.line_items << Payday::LineItem.new(
    :price => paypal_params['mc_gross'],
    :quantity => 1,
    :description => paypal_params['item_name'])
  invoice.notes = "Thank you for your purchase!"
  invoice.render_pdf
end

Obviously, you will want to adjust this code to fit what you are selling. In my case, there is always only one line item in my transactions.

Finally, I make the invoice downloadable from the user account page. The controller method works like this :

# app/controllers/payments_controller.rb
def pdf_invoice
  payment = Payment.find_by_tx_id! params[:id]
  respond_to do |format|
    format.pdf do
      send_data payment.generate_pdf_invoice,
        :filename => payment.invoice_filename,
        :type => "application/pdf"  , :disposition => "inline"
    end
  end
end

Again, you will probably have to adjust this method for your own needs. Don’t forget to add the pdf mime type to the mime_types.rb initializer :

# /config/initializers/mime_types.rb
Mime::Type.register 'application/pdf', :pdf

There’s a lot more you can do with Payday. It supports I18n and it integrates well with ActiveRecord. I encourage you to take a look at the readme on github.