Rack to serve statics files with a middleware

static_file_server_rack.rb

require 'rack/utils'
module Openair
  class MediaKitStaticRack
    def initialize
      @middlewares = [:bugsnag]
      @middlewares << :errors unless Rails.env.development?
    end

    def call(env)
      @app = load_app
      @app.call(env)
    end

    private

    def load_app
      @app ||= @middlewares.reduce(Base.new) do |app, middleware|
        app = self.send("initialize_middleware_#{middleware}", app)
      end
    end

    def initialize_middleware_bugsnag(app)
      Bugsnag::Rack.new(app)
    end

    def initialize_middleware_errors(app)
      ActionDispatch::ShowExceptions.new(app, 
                                         ActionDispatch::PublicExceptions.new("#{Rails.root}/public"))
    end

    class Base
      def call(env)
        path = env["SERVER_NAME"]
        file, headers = pick_file_and_headers_for_path(path, env)
        ::Rack::File.new(file, headers).call(env)
      end


      private

      def get_best_encoding(request)
        Rack::Utils.select_best_encoding(%w(gzip identity), request.accept_encoding)
      end

      def headers
        @headers ||= {'Content-Type' => 'text/html' }
      end

      def pick_file_and_headers_for_path(path, env)
        request = Rack::Request.new(env)
        encoding = get_best_encoding(request)
        file = "#{Rails.root.to_s}/public/media_kits/" + path + '.html'
        if File.exist?(file)
          if encoding == 'gzip'
            file = file + '.gz'
            headers['Content-Encoding'] = 'gzip'
          end
        else
          raise ActionController::RoutingError.exception("Page Not Found")
        end
        [file, headers]
      end
    end
  end
end