module DoubleTrouble
  module Protection
    def self.included(base)
      base.class_eval do
        class_inheritable_accessor :allow_double_trouble_protection
        cattr_accessor             :double_trouble_nonce_store
        cattr_accessor             :double_trouble_nonce_param
        helper_method              :protect_against_double_trouble?, :double_trouble_nonce_param, :double_trouble_form_nonce

        self.allow_double_trouble_protection = true

        extend(ClassMethods)
      end
    end

    module ClassMethods
      def protect_from_double_trouble(resource_name, options = {})
        self.double_trouble_nonce_param   ||= :form_nonce
        self.double_trouble_nonce_store   ||= CachedNonce

        around_filter(options.slice(:only, :except)) do |controller, action_block|
          if controller.send(:protect_against_double_trouble?)
            nonce = controller.params[double_trouble_nonce_param]

            double_trouble_nonce_store.valid?(nonce) || raise(InvalidNonce)

            action_block.call

            controller.instance_variable_get("@#{resource_name}").tap do |resource|
              resource.present? && !resource.new_record? && double_trouble_nonce_store.store!(nonce)
            end
          else
            action_block.call
          end
        end
      end
    end

    protected

    def double_trouble_form_nonce
      ActiveSupport::SecureRandom.base64(32)
    end

    def protect_against_double_trouble?
      allow_double_trouble_protection && double_trouble_nonce_store && double_trouble_nonce_param
    end
  end
end