def credit_card
    @credit_card ||= ActiveMerchant::Billing::CreditCard.new(
      :type               => card_type,
      :number             => card_number,
      :verification_value => card_verification,
      :month              => card_expires_on.month,
      :year               => card_expires_on.year,
      :first_name         => first_name,
      :last_name          => last_name,
      :billing_address    => billing_address,
      :billing_city       => billing_city,
      :billing_state      => billing_state,
      :billing_zip        => billing_zip
    )
  end
end