Simple written "Model Concern" for adding active merchant

as_active_merchant.rb

# Integrate with ActiveMerchant and Expose active merchant related methods.
#
# This module also includes Validator for ActiveMerchant.
module Concerns::AsActiveMerchant
  extend ActiveSupport::Concern

  included do
    validates_with Validators::ActiveMerchant, if: :cc_number_is_changed?
  end

  def cc_number_is_changed?
    new_record? || changed_attributes['number'].present?
  end

  # Create ActiveMerchant::Billing::CreditCard object instance from the instance
  # data.
  #
  # Returns ActiveMerchant::Billing::CreditCard instance
  def as_active_merchant
    attrs = { brand:      self.brand,
              first_name: self.first_name,
              last_name:  self.last_name,
              number:     self.number,
              month:      self.month,
              year:       self.year }

    if self.verification_value.present?
      attrs[:verification_value] = self.verification_value
    end

    ActiveMerchant::Billing::CreditCard.new attrs
  end

  def display_number
    as_active_merchant.display_number
  end

  module ClassMethods
    # Return list of credit card brand names
    def brands
      ActiveMerchant::Billing::CreditCard.card_companies.keys
    end
  end

  module Validators
    class ActiveMerchant < ActiveModel::Validator

      def validate(record)
        am_cc = record.as_active_merchant

        unless am_cc.valid?
          record.errors[:base] << 'Invalid Credit Card Information'
          am_cc.errors.each do |k, v|
            record.errors[k] = v.join(', ')
          end
        end
      end
    end
  end
end