// raftEventLogger converts events from the Raft server into log messages.
func (s *PeerServer) raftEventLogger(event raft.Event) {
	value := event.Value()
	prevValue := event.PrevValue()
	if value == nil {
		value = "<nil>"
	}
	if prevValue == nil {
		prevValue = "<nil>"
	}

	switch event.Type() {
	case raft.StateChangeEventType:
		log.Infof("%s: state changed from '%v' to '%v'.", s.Config.Name, prevValue, value)
	case raft.TermChangeEventType:
		log.Infof("%s: term #%v started.", s.Config.Name, value)
	case raft.LeaderChangeEventType:
		log.Infof("%s: leader changed from '%v' to '%v'.", s.Config.Name, prevValue, value)
	case raft.AddPeerEventType:
		log.Infof("%s: peer added: '%v'", s.Config.Name, value)
	case raft.RemovePeerEventType:
		log.Infof("%s: peer removed: '%v'", s.Config.Name, value)
	case raft.HeartbeatIntervalEventType:
		var name = "<unknown>"
		if peer, ok := value.(*raft.Peer); ok {
			name = peer.Name
		}
		log.Infof("%s: warning: heartbeat timed out: '%v'", s.Config.Name, name)
	case raft.ElectionTimeoutThresholdEventType:
		select {
		case s.timeoutThresholdChan <- value:
		default:
		}

	}
}
func (s *PeerServer) recordMetricEvent(event raft.Event) {
	name := fmt.Sprintf("raft.event.%s", event.Type())
	value := event.Value().(time.Duration)
	(*s.metrics).Timer(name).Update(value)
}