require 'securerandom'
require 'active_support/core_ext/string/access'
require 'active_support/core_ext/object/blank'

# Backported from Rails 3.2 (ActionDispatch::RequestId)
module MetaRequest
  module Middlewares
    # Makes a unique request id available to the action_dispatch.request_id env variable (which is then accessible through
    # ActionDispatch::Request#uuid) and sends the same id to the client via the X-Request-Id header.
    #
    # The unique request id is either based off the X-Request-Id header in the request, which would typically be generated
    # by a firewall, load balancer, or the web server, or, if this header is not available, a random uuid. If the
    # header is accepted from the outside world, we sanitize it to a max of 255 chars and alphanumeric and dashes only.
    #
    # The unique request id can be used to trace a request end-to-end and would typically end up being part of log files
    # from multiple pieces of the stack.
    class RequestId
      def initialize(app)
        @app = app
      end

      def call(env)
        env["action_dispatch.request_id"] = external_request_id(env) || internal_request_id
        status, headers, body = @app.call(env)

        headers["X-Request-Id"] = env["action_dispatch.request_id"]
        [ status, headers, body ]
      end

      private
        def external_request_id(env)
          if request_id = env["HTTP_X_REQUEST_ID"].presence
            request_id.gsub(/[^\w\-]/, "").first(255)
          end
        end

        def internal_request_id
          SecureRandom.hex(16)
        end
    end
  end
end
