code: def timeline(self):
          
          if self.history:
              if self.history.lines:
                  try:
                      return int(self.history.lines[-1][0]) + 1
                  except Exception:
                      logger.error('Failed to parse cluster history from DCS: %s', self.history.lines)
              elif self.history.value == '[]':
                  return 1
          return 0
docs: >>> Cluster(0, 0, 0, 0, 0, 0, 0, 0).timeline
          0
          >>> Cluster(0, 0, 0, 0, 0, 0, 0, TimelineHistory.from_node(1, '[]')).timeline
          1
          >>> Cluster(0, 0, 0, 0, 0, 0, 0, TimelineHistory.from_node(1, '[["a"]]')).timeline
          0