Gateway::UsaEpay

application.rb

# config/application.rb

module YourApp
  class Application < Rails::Application
    
    require 'spree_site'

    # ...

  end
end

spree_site.rb

# lib/spree_site.rb

module SpreeSite
  class Engine < Rails::Engine
       
    def self.activate
      Gateway::UsaEpay.register      
    end
    
    config.to_prepare &method(:activate).to_proc
  end
end

usa_epay.rb

# app/models/gateway/usa_epay.rb

class Gateway::UsaEpay < Gateway
  
  preference :login, :string

  def provider_class
    ActiveMerchant::Billing::UsaEpayGateway
  end
    
end