Enable :background => true option for active record callbacks + "send_later"

background_callbacks.rb

ActiveRecord::Base.class_eval do
  public :callback

  def self.define_background_callback(callback_name)
    class_eval <<-RUBY
      define_callbacks :background_#{callback_name}           # define_callbacks :background_after_create
                                                              #
      #{callback_name} do |object|                            # after_create do |object|
        object.queue_background_callbacks(:#{callback_name})  #   object.queue_background_callbacks(:after_create)
      end                                                     # end
                                                              #
      def self.#{callback_name}_with_background(*methods)     # def self.after_create_with_background(*methods)
        options = methods.extract_options!                    #   options = methods.extract_options!
        methods.push(options.except(:background))             #   methods.push(options.except(:background))
                                                              #
        if options[:background]                               #   if options[:background]
          background_#{callback_name}(*methods)               #     background_after_create(*methods)
        else                                                  #   else
          #{callback_name}_without_background(*methods)       #     after_create_without_background(*methods)
        end                                                   #   end
      end                                                     # end
                                                              #
      class << self                                           # class << self
        alias_method_chain :#{callback_name}, :background     #   alias_method_chain :after_create, :background
      end                                                     # end
    RUBY
  end

  BACKGROUND_CALLBACKS = [:after_save, :after_create, :after_update]

  BACKGROUND_CALLBACKS.each do |callback_name|
    define_background_callback callback_name
  end

  def queue_background_callbacks(callback_name)
    return if self.class.send("background_#{callback_name}_callback_chain").empty?
    send_later(:run_background_callbacks, callback_name)
  end

  def run_background_callbacks(callback_name)
    ActiveRecord::Base.transaction do
      callback("background_#{callback_name}".to_sym)
    end
  end
end