middleware.rb

# frozen_string_literal: true

require "active_support/core_ext/string/strip"
require "json"

module WebConsole
  class Middleware
    TEMPLATES_PATH = File.expand_path("../templates", __FILE__)

    cattr_accessor :mount_point, default: "/__web_console"
    cattr_accessor :whiny_requests, default: true

    def initialize(app)
      @app = app
    end

    def call(env)
      app_exception = catch :app_exception do
        request = create_regular_or_whiny_request(env)
        return call_app(env) unless request.permitted?

        if id = id_for_repl_session_update(request)
          return update_repl_session(id, request)
        elsif id = id_for_repl_session_stack_frame_change(request)
          return change_stack_trace(id, request)
        end


        status, headers, body = call_app(env)

        if (session = Session.from(Thread.current)) && acceptable_content_type?(headers)
          headers["x-web-console-session-id"] = session.id
          headers["x-web-console-mount-point"] = mount_point

          template = Template.new(env, session)
          body, headers = Injector.new(body, headers).inject(template.render("index"))
        end

        [ status, headers, body ]
      end
    rescue => e
      WebConsole.logger.error("\n#{e.class}: #{e}\n\tfrom #{e.backtrace.join("\n\tfrom ")}")
      raise e
    ensure
      # Clean up the fiber locals after the session creation. Object#console
      # uses those to communicate the current binding or exception to the middleware.
      Thread.current[:__web_console_exception] = nil
      Thread.current[:__web_console_binding] = nil

      raise app_exception if Exception === app_exception
    end

    private

      def acceptable_content_type?(headers)
        headers["content-type"].to_s.include?("html")
      end

      def json_response(opts = {})
        status  = opts.fetch(:status, 200)
        headers = { "content-type" => "application/json; charset = utf-8" }
        body    = yield.to_json

        [ status, headers, [ body ] ]
      end

      def json_response_with_session(id, request, opts = {})
        return respond_with_unavailable_session(id) unless session = Session.find(id)

        json_response(opts) { yield session }
      end

      def create_regular_or_whiny_request(env)
        request = Request.new(env)
        whiny_requests ? WhinyRequest.new(request) : request
      end

      def repl_sessions_re
        @_repl_sessions_re ||= %r{#{mount_point}/repl_sessions/(?<id>[^/]+)}
      end

      def update_re
        @_update_re ||= %r{#{repl_sessions_re}\z}
      end

      def binding_change_re
        @_binding_change_re ||= %r{#{repl_sessions_re}/trace\z}
      end

      def id_for_repl_session_update(request)
        if request.xhr? && request.put?
          update_re.match(request.path) { |m| m[:id] }
        end
      end

      def id_for_repl_session_stack_frame_change(request)
        if request.xhr? && request.post?
          binding_change_re.match(request.path) { |m| m[:id] }
        end
      end

      def update_repl_session(id, request)
        json_response_with_session(id, request) do |session|
          if input = request.params[:input]
            { output: session.eval(input) }
          elsif input = request.params[:context]
            { context: session.context(input) }
          end
        end
      end

      def change_stack_trace(id, request)
        json_response_with_session(id, request) do |session|
          session.switch_binding_to(request.params[:frame_id], request.params[:exception_object_id])

          { ok: true }
        end
      end

      def respond_with_unavailable_session(id)
        json_response(status: 404) do
          { output: format(I18n.t("errors.unavailable_session"), id: id) }
        end
      end

      def respond_with_unacceptable_request
        json_response(status: 406) do
          { output: I18n.t("errors.unacceptable_request") }
        end
      end

      def call_app(env)
        @app.call(env)
      rescue => e
        throw :app_exception, e
      end
  end
end