docs: def current_sleep_stage(self):
          """Return sleep stage for in-progress session."""
          try:
              stages = self.intervals[0]['stages']
              num_stages = len(stages)
  
              if num_stages == 0:
                  return None
  
              # API now always has an awake state last in the dict
              # so always pull the second to last stage while we are
              # in a processing state
              if self.current_session_processing:
                  stage = stages[num_stages-2]['stage']
              else:
                  stage = stages[num_stages-1]['stage']
  
              # UNRELIABLE... Removing for now.
              # Check sleep stage against last_seen time to make
              # sure we don't get stuck in a non-awake state.
              #delta_elap = datetime.fromtimestamp(time.time()) \
              #    - datetime.strptime(self.last_seen, '%Y-%m-%dT%H:%M:%S')
              #_LOGGER.debug('User elap: %s', delta_elap.total_seconds())
              #if stage != 'awake' and delta_elap.total_seconds() > 1800:
                  # Bed hasn't seen us for 30min so set awake.
              #    stage = 'awake'
          except KeyError:
              stage = None
          return stage