text: from collections import defaultdict
  from enum import Enum
  import logging
  import threading
  from logging.handlers import TimedRotatingFileHandler
  
  import torch.multiprocessing as mp
  from .errors import NoRunnerException
  import time
  
  
  class Events(Enum):
      """
      Events that are fired by the :class:`~core.RoutineInterface` during
      execution."""
      BEFORE_LOGIC = "before_logic"
      AFTER_LOGIC = "after_logic"
      EXCEPTION_RAISED = "exception_raised"
  
  
  class State(object):
      """
      An object that is used to pass internal and user-defined state between
      event handlers."""
  
      def __init__(self):
          self.count = 0
          self.success = 0
          self.output = None
  
  
  class Routine:
  
      def __init__(self, name="", component_name=""):
  
          self.name = name
  
          # name of the component that instantiated the routine
          self.component_name = component_name
  
          self.stop_event: mp.Event = None
          self._event_handlers = defaultdict(list)
          self.state = None
          self._allowed_events = []
          self.register_events(*Events)
          self.runner = None
          self._setup_logger()
  
      def _setup_logger(self):
          # setting up the routine's logger
          self.logger = logging.getLogger(self.component_name + "." +
                                          self.name)
          self.logger.setLevel(logging.DEBUG)
          self.logger.propagate = False
          log_file = "pipeline.log"
          file_handler = TimedRotatingFileHandler(log_file, when='midnight')
          file_handler.setFormatter(logging.Formatter(
              "%(asctime)s — %(name)s — %(levelname)s — %(message)s"))
          self.logger.addHandler(file_handler)
  
      def register_events(self, *event_names):
          """
          Add events that can be fired.
  
          Registering an event will let the user fire these events at any point.
          This opens the door to make the :meth:`~ignite.engine.Engine.run` loop
          even more configurable.
  
          By default, the events from :class:`~ignite.engine.Events` are
          registerd.
  
          Args:
              *event_names: An object (ideally a string or int) to define the
                  name of the event being supported.
  
          Example usage:
  
          .. code-block:: python
  
              from enum import Enum
  
              class Custom_Events(Enum):
                  FOO_EVENT = "foo_event"
                  BAR_EVENT = "bar_event"
  
              engine = Engine(process_function)
              engine.register_events(*Custom_Events)
  
          """
          for name in event_names:
              self._allowed_events.append(name)
  
      def add_event_handler(self, event_name, handler, first=False,
                            last=False, *args, **kwargs):
          """
          Add an event handler to be executed when the specified event is
          fired.
  
          Args:
              event_name: An event to attach the handler to. Valid events are
              from :class:`~ignite.engine.Events` or any `event_name` added by
               :meth:`~ignite.engine.Engine.register_events`.
              handler (callable): the callable event handler that
              should be invoked
              first: specify 'true' if the event handler should be called first
              last: specify 'true' if the event handler should be called last
              *args: argsional args to be passed to `handler`.
              **kwargs: argsional keyword args to be passed to `handler`.
  
          Notes:
                The handler function's first argument will be `self`, the
                :class:`~ignite.engine.Engine` object it was bound to.
  
                Note that other arguments can be passed to the handler in
                addition to the `*args` and  `**kwargs` passed here, for example
                 during :attr:`~ignite.engine.Events.EXCEPTION_RAISED`.
  
          Example usage:
  
          .. code-block:: python
  
              engine = Engine(process_function)
  
              def print_epoch(engine):
                  print("Epoch: {}".format(engine.state.epoch))
  
              engine.add_event_handler(Events.EPOCH_COMPLETED, print_epoch)
  
          """
          if event_name not in self._allowed_events:
              self.logger.error("attempt to add event handler to an invalid "
                                "event %s.", event_name)
              raise ValueError("Event {} is not a valid event for this "
                               "Engine.".format(event_name))
  
          if first:
              self._event_handlers[event_name].append((0,
                                                       (handler, args, kwargs)))
          elif last:
              self._event_handlers[event_name].append((2,
                                                       (handler, args, kwargs)))
          else:
              self._event_handlers[event_name].append((1,
                                                       (handler, args, kwargs)))
  
          # Sort the event handler list in an ascending order by the priority
          # in order to guarantee an execution order of the handlers.
          self._event_handlers[event_name] = \
              sorted(self._event_handlers[event_name], key=lambda x: x[0])
          self.logger.debug("added handler for event %s.", event_name)
  
      def has_event_handler(self, handler, event_name=None):
          """
          Check if the specified event has the specified handler.
  
          Args:
              handler (callable): the callable event handler.
              event_name: The event the handler attached to. Set this
                  to ``None`` to search all events.
          """
          if event_name is not None:
              if event_name not in self._event_handlers:
                  return False
              events = [event_name]
          else:
              events = self._event_handlers
          for e in events:
              for priority, (h, _, _) in self._event_handlers[e]:
                  if h == handler:
                      return True
          return False
  
      def remove_event_handler(self, handler, event_name):
          """
          Remove event handler `handler` from registered handlers of the
          engine
  
          Args:
              handler (callable): the callable event handler that should
              be removed
              event_name: The event the handler attached to.
  
          """
          if event_name not in self._event_handlers:
              raise ValueError(f"Input event name '{event_name}' does not exist")
  
          current_event_handlers = self._event_handlers[event_name]
          new_event_handlers = [(priority, h) for priority, h in
                                current_event_handlers if h[0] != handler]
          if len(new_event_handlers) == len(current_event_handlers):
              raise ValueError("Input handler '{}' is not found among registered"
                               " event handlers".format(handler))
          self._event_handlers[event_name] = new_event_handlers
  
      def pace(self, fps):
          """
          Pace the routine to work at a wanted fps
  
          Args:
              fps: The wanted fps for the routine
          """
          def start_time(routine: Routine):
              routine.state.start_time = time.time()
  
          def start_pacing(routine: Routine, required_fps=0):
              if routine.state.output:
                  elapsed_time = (time.time() - routine.state.start_time)
                  excess_time = (1 / required_fps) - elapsed_time
                  if excess_time > 0:
                      time.sleep(excess_time)
  
          self.add_event_handler(Events.BEFORE_LOGIC, start_time, first=True)
          self.add_event_handler(Events.AFTER_LOGIC,
                                 start_pacing,
                                 last=True,
                                 required_fps=fps)
  
      def on(self, event_name, *args, **kwargs):
          """
          Decorator shortcut for add_event_handler.
  
          Args:
              event_name: An event to attach the handler to. Valid events are
              from :class:`~ignite.engine.Events` or any `event_name` added by
               :meth:`~ignite.engine.Engine.register_events`.
              *args: argsional args to be passed to `handler`.
              **kwargs: argsional keyword args to be passed to `handler`.
  
          """
          def decorator(f):
              self.add_event_handler(event_name, f, *args, **kwargs)
              return f
          return decorator
  
      def _fire_event(self, event_name, *event_args, **event_kwargs):
          """
          Execute all the handlers associated with given event.
  
          This method executes all handlers associated with the event
          `event_name`. Optional positional and keyword arguments can be used to
          pass arguments to **all** handlers added with this event. These
          aguments updates arguments passed using
          :meth:`~ignite.engine.Engine.add_event_handler`.
  
          Args:
              event_name: event for which the handlers should be executed. Valid
                  events are from :class:`~ignite.engine.Events` or any
                  `event_name` added by
                   :meth:`~ignite.engine.Engine.register_events`.
              *event_args: argsional args to be passed to all handlers.
              **event_kwargs: argsional keyword args to be passed to
              all handlers.
  
          """
          if event_name in self._allowed_events:
              # self.logger.debug("firing handlers for event %s ", event_name)
              for p, (func, args, kwargs) in self._event_handlers[event_name]:
                  kwargs.update(event_kwargs)
                  func(self, *(event_args + args), **kwargs)
  
      def main_logic(self, *args, **kwargs):
          raise NotImplementedError
  
      def setup(self, *args, **kwargs):
          raise NotImplementedError
  
      def cleanup(self, *args, **kwargs):
          raise NotImplementedError
  
      # TODO - replace plain 'setup()' and 'cleanup()' with context manager
      def _extended_run(self):
          """
  
          Returns:
  
          """
          self.state = State()
          # TODO - how to pass different args to setup/cleanup/main_logic?
          self.setup()
          # TODO - maybe add _fire_event before and after the while loop?
          while not self.stop_event.is_set():
              self._fire_event(Events.BEFORE_LOGIC)
              self.state.output = self.main_logic()
              self.state.count += 1
              if self.state.output:
                  self.state.success += 1
              self._fire_event(Events.AFTER_LOGIC)
  
          self.cleanup()
  
      def as_thread(self):
          self.runner = threading.Thread(target=self._extended_run)
          return self
  
      def as_process(self):
          self.runner = mp.Process(target=self._extended_run)
          return self
  
      def start(self):
          if self.runner is None:
              # TODO - create better errors
              raise NoRunnerException("Runner not configured for routine")
          self.runner.start()
  