My IPN model.

ipn.rb

class Ipn < ActiveRecord::Base
  belongs_to :user
  serialize  :message_data, Hash  

  #
  # Return true if this is a payment.
  #
  def payment?
    return paypal_subscription_payment? || weblaws_payment?
  end

  #
  # Return the dollar amount of the IPN.  This makes most sense if
  # it's a payment or a subscription.
  #
  def amount
    if paypal_subscription_payment?
      return message_data['payment_gross']
    elsif weblaws_payment?
      return message_data['weblaws_payment_amt']
    else
      raise 'No amount in this IPN'
    end
  end
  
  
  #
  # Supporting the Paypal protocol
  #
  
  def paypal_subscription_payment?
    return message_data['txn_type'] == 'subscr_payment'
  end
  
  
  
  #
  # An alternate way to give a user "payment":
  # A weblaws payment consists of an arbitrary amount
  # (even zero), and an expiration date.
  #
  # weblaws_payment         - boolean
  # weblaws_payment_amt     - int
  # weblaws_expiration_date - date the payment expires
  #
  
  #
  # Is this a weblaws_payment?
  #
  def weblaws_payment?
    message_data['weblaws_payment'] == true
  end
  
  def expiration_date
    message_data['weblaws_expiration_date']
  end
  
  def has_expiration_date?
    expiration_date != nil
  end
end