module MyFeeds
  module Identity
    extend ActiveSupport::Concern

    included do
      before_save :save_feed_identity
      init_feeds_polymorphic :source if self == Feed
      delegate :polymorphic_identity_column, :polymorphic_id_column, :polymorphic_type_column, to: :"self.class"
    end

    module ClassMethods
      def feed_polymorphic
        @_feed_polymorphic
      end

      def init_feeds_polymorphic polymorphic
        @_feed_polymorphic = polymorphic
        class_eval %Q{
          def save_feed_identity
            self.#{polymorphic_identity_column} = "#\{#{polymorphic_id_column}.to_s\}:#\{#{polymorphic_type_column}.to_s.underscore\}"
          end
          protected :save_feed_identity
        }
      end

      def polymorphic_identity_column
        :"#{feed_polymorphic}_identity"
      end

      def polymorphic_id_column
        :"#{feed_polymorphic}_id"
      end

      def polymorphic_type_column
        :"#{feed_polymorphic}_type"
      end
    end
  end
end