module ActionController
  # Dispatches requests to the appropriate controller and takes care of
  # reloading the app after each request when Dependencies.load? is true.
  class Dispatcher
    @@guard = Mutex.new

    class << self
      def define_dispatcher_callbacks(cache_classes)
        unless cache_classes
          # Development mode callbacks
          before_dispatch :reload_application
          after_dispatch :cleanup_application
        end

        if defined?(ActiveRecord)
          after_dispatch :checkin_connections
          to_prepare(:activerecord_instantiate_observers) { ActiveRecord::Base.instantiate_observers }
        end

        after_dispatch :flush_logger if Base.logger && Base.logger.respond_to?(:flush)

        to_prepare do
          I18n.reload!
        end
      end

      # DEPRECATE: Remove CGI support
      def dispatch(cgi = nil, session_options = CgiRequest::DEFAULT_SESSION_OPTIONS, output = $stdout)
        new(output).dispatch_cgi(cgi, session_options)
      end

      # Add a preparation callback. Preparation callbacks are run before every
      # request in development mode, and before the first request in production
      # mode.
      #
      # An optional identifier may be supplied for the callback. If provided,
      # to_prepare may be called again with the same identifier to replace the
      # existing callback. Passing an identifier is a suggested practice if the
      # code adding a preparation block may be reloaded.
      def to_prepare(identifier = nil, &block)
        @prepare_dispatch_callbacks ||= ActiveSupport::Callbacks::CallbackChain.new
        callback = ActiveSupport::Callbacks::Callback.new(:prepare_dispatch, block, :identifier => identifier)
        @prepare_dispatch_callbacks.replace_or_append!(callback)
      end
    end

    cattr_accessor :middleware
    self.middleware = MiddlewareStack.new
    self.middleware.use "ActionController::Failsafe"

    include ActiveSupport::Callbacks
    define_callbacks :prepare_dispatch, :before_dispatch, :after_dispatch

    # DEPRECATE: Remove arguments
    def initialize(output = $stdout, request = nil, response = nil)
      @output, @request, @response = output, request, response
      @app = @@middleware.build(lambda { |env| self.dup._call(env) })
    end

    def dispatch_unlocked
      begin
        run_callbacks :before_dispatch
        handle_request
      rescue Exception => exception
        failsafe_rescue exception
      ensure
        run_callbacks :after_dispatch, :enumerator => :reverse_each
      end
    end

    def dispatch
      if ActionController::Base.allow_concurrency
        dispatch_unlocked
      else
        @@guard.synchronize do
          dispatch_unlocked
        end
      end
    end

    # DEPRECATE: Remove CGI support
    def dispatch_cgi(cgi, session_options)
      CGIHandler.dispatch_cgi(self, cgi, @output)
    end

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

    def _call(env)
      @request = RackRequest.new(env)
      @response = RackResponse.new(@request)
      dispatch
    end

    def reload_application
      # Run prepare callbacks before every request in development mode
      run_callbacks :prepare_dispatch

      Routing::Routes.reload
      ActionView::Helpers::AssetTagHelper::AssetTag::Cache.clear
    end

    # Cleanup the application by clearing out loaded classes so they can
    # be reloaded on the next request without restarting the server.
    def cleanup_application
      ActiveRecord::Base.reset_subclasses if defined?(ActiveRecord)
      ActiveSupport::Dependencies.clear
      ActiveRecord::Base.clear_reloadable_connections! if defined?(ActiveRecord)
    end

    def flush_logger
      Base.logger.flush
    end

    def checkin_connections
      # Don't return connection (and peform implicit rollback) if this request is a part of integration test
      # TODO: This callback should have direct access to env
      return if @request.key?("action_controller.test")
      ActiveRecord::Base.clear_active_connections!
    end

    protected
      def handle_request
        @controller = Routing::Routes.recognize(@request)
        @controller.process(@request, @response).out
      end

      def failsafe_rescue(exception)
        if @controller ||= (::ApplicationController rescue Base)
          @controller.process_with_exception(@request, @response, exception).out
        else
          raise exception
        end
      end
  end
end