Simple Banking module

outline

app/
  models/
    user.rb # ActiveRecord
    banking/
      payment_methods/
        bank_account.rb # ActiveRecord
        credit_card.rb # ActiveRecord
        registration.rb
      processing/
        base.rb
        debit.rb
        void.rb
        credit.rb
        refund.rb
      errors/
        invalid_amount.rb
        invalid_credit_card_number.rb
        invalid_routing_number.rb
        unregistered_payment_method.rb
      transaction.rb # ActiveRecord