gistfile1.rb

module PerActionMiddleware
  # DUMMY MODULE, just to get the file loaded. 
end

module ActionController
  class Base
    class << self

      alias _call call
      def call(env)
        action = env["rack.routing_args"]["action"]
        @@app ||= prepare_mw_stack(action)
        @@middle_stack ||= {}
        @@app.call(env)
      end

      def middles
        @middles ||= []
      end

      def middle(app, *options)
        options = options.pop || {}
        middles.push(app)
        Array(options[:only]).each {|action| middleware_whitelist[app] << action.to_sym }
        Array(options[:except]).each {|action| middleware_blacklist[app] << action.to_sym }
      end

      def middleware_whitelist
        @middleware_whitelist ||= Hash.new {|h,k| h[k] = [] }
      end

      def middleware_blacklist
        @middleware_blacklist ||= Hash.new {|h,k| h[k] = [] }
      end

      def can_use_middleware?(mw, action)
        return true if middleware_whitelist[mw].include?(action.to_sym)
        return false if middleware_blacklist[mw].include?(action.to_sym)
        return true if middleware_whitelist[mw].empty?
      end

      def prepare_mw_stack(action)
        @@middle_stack ||= {}
        @@middle_stack[action] ||= MiddlewareStack.new do |middleware|
          self.middles.each do |mw|
            middleware.use(mw) if  can_use_middleware?(mw, action)
          end
        end
        @@middle_stack[action].build(lambda {|env| _call(env)})
      end
    end
  end
end