easy-going-rails/lib/semantic/dev_loader.rb

module Semantic
  # use the Zeitwerk autoloader to reattach_appender for development autoreloading feature
  class DevLoader
    def initialize(session_key)
      @session_key = session_key

      force_preload_module
      RailsSemanticLogger::ActionController::LogSubscriber.logger.level = :fatal # useful for remanent Rack::Log started

      once_and_reload do
        clear_subscribers(/\.action_controller$/)
        clear_subscribers(/\.action_view$/)

        append_ansi_formatter
        reset_subscribers
        register_log_subscriber
      end
    end

    private

    def once_and_reload(&)
      yield
      Rails.autoloaders.main.on_load('ApplicationController', &)
    end

    def force_preload_module
      self.class.module_parent.constants.each { |const| self.class.module_parent.const_get(const) }
    end

    def append_ansi_formatter
      SemanticLogger.clear_appenders!
      formatter = Semantic::AnsiFormatter.new
      SemanticLogger.add_appender(io: $stdout,
                                  formatter:,
                                  filter: ->(log) { !formatter.reject(log) })
    end

    def register_log_subscriber
      register_to_action_controller(:start_processing)
      register_to_action_controller(:process_action, :finish_processing)
      register_to_action_controller(:redirect_to)
      %i[send_file send_data halted_callback unpermitted_parameters send_stream write_fragment
         read_fragment expire_fragment exist_fragment?].each do |hook|
        register_to_action_controller(hook, :any_hook)
      end
    end

    def register_to_action_controller(hook, method = hook)
      @subscribers << ActiveSupport::Notifications.subscribe("#{hook}.action_controller") do |event|
        @log_subscriber.send(method, event)
      end
    end

    def subscriber_patterns(subscriber)
      subscriber.patterns.respond_to?(:keys) ? subscriber.patterns.keys : subscriber.patterns
    end

    def unattach(subscriber, pattern)
      subscriber_patterns(subscriber).each do |sub_pattern|
        ActiveSupport::Notifications.notifier.listeners_for(sub_pattern).each do |sub|
          next unless sub.instance_variable_get(:@delegate) == subscriber
          next unless pattern.match(sub_pattern)

          puts "FOUND subscriber=#{subscriber} for sub_pattern=#{sub_pattern} with logger #{subscriber.logger.name}"
          puts subscriber.class.module_parent.const_source_location(subscriber.class.to_s)&.first

          ActiveSupport::Notifications.unsubscribe(sub)
        end
      end
      ActiveSupport::LogSubscriber.subscribers.delete(subscriber)
    end

    # pattern could be either a string 'start_processing.action_controller' or a regex /\.action_controller$/
    def clear_subscribers(pattern)
      ActiveSupport::LogSubscriber.subscribers.each { |sub| unattach(sub, pattern) }
    end

    def reset_subscribers
      if defined?(@subscribers)
        @subscribers.each do |sub|
          ActiveSupport::Notifications.unsubscribe(sub)
        end
        @subscribers.clear
      else
        @subscribers = []
      end

      @log_subscriber = Semantic::LogSubscriber.new(@session_key)
    end
  end
end