func activate(st *store.Store, self string, c *doozer.Client) int64 {
	w := store.NewWatch(st, calGlob)

	for _, base := range store.Getdir(st, calDir) {
		p := calDir + "/" + base
		v, rev := st.Get(p)
		if rev != store.Dir && v[0] == "" {
			seqn, err := c.Set(p, rev, []byte(self))
			if err != nil {
				log.Println(err)
				continue
			}

			w.Stop()
			return seqn
		}
	}

	for ev := range w.C {
		// TODO ev.IsEmpty()
		if ev.IsSet() && ev.Body == "" {
			seqn, err := c.Set(ev.Path, ev.Rev, []byte(self))
			if err != nil {
				log.Println(err)
				continue
			}
			w.Stop()
			return seqn
		}
	}

	return 0
}

func mustWait(s *store.Store, n int64) <-chan store.Event {
	c, err := s.Wait(store.Any, n)
	if err != nil {
		panic(err)
	}
	return c
}

func Clean(s *store.Store, p paxos.Proposer) {
	timer := timer.New("/session/**", timer.OneSecond, s)
	for tick := range timer.C {
		_, cas := s.Get(tick.Path)
		paxos.Del(p, tick.Path, cas)
	}
}

// This thing keeps track of who is supposed to be in the cluster for every
// seqn. It also remembers the network address of every member.
// TODO remove the `start` param when store.Get provides a version
func NewRegistrar(st *store.Store, start uint64, alpha int) *Registrar {
	rg := &Registrar{
		alpha:    alpha,
		st:       st,
		evs:      st.Watch("**"), // watch absolutely everything
		lookupCh: make(chan *lookup),
		lookups:  new(lookupQueue),
	}
	go rg.process(start, readdirMap(st, membersKey), readdirMap(st, slotKey))
	return rg
}

func Clean(st *store.Store) {
	cl := &cleaner{
		st:     st,
		table:  make(map[string]uint64),
		logger: util.NewLogger("clean"),
	}

	for ev := range st.Watch("/doozer/info/*/applied") {
		cl.update(ev)
		cl.check()
	}
}

func Clean(c chan string, st *store.Store, p consensus.Proposer) {
	for addr := range c {
		_, g := st.Snap()
		name := getName(addr, g)
		if name != "" {
			go func() {
				clearSlot(p, g, name)
				removeInfo(p, g, name)
			}()
		}
	}
}

func readdirMap(st *store.Store, path string) map[string]string {
	m := map[string]string{}
	keys, cas := st.Get(path)
	if cas != store.Dir {
		return map[string]string{}
	}
	for _, key := range keys {
		v, cas := st.Get(path + "/" + key)
		if cas != store.Dir && cas != store.Missing {
			m[key] = v[0]
		}
	}
	return m
}

func Clean(st *store.Store, p paxos.Proposer) {
	logger := util.NewLogger("member")
	for ev := range st.Watch("/session/*") {
		if !ev.IsDel() {
			continue
		}

		parts := strings.Split(ev.Path, "/", 3)
		name := parts[2]
		logger.Printf("lost session %s", name)

		clearSlot(p, ev, name)
		removeMember(p, ev, name)
		removeInfo(p, ev, name)
	}
}

func walk(path string, st *store.Store, ch chan store.Event) {
	for path != "/" && strings.HasSuffix(path, "/") {
		// TODO generalize and factor this into pkg store.
		path = path[0 : len(path)-1]
	}
	v, rev := st.Get(path)
	if rev != store.Dir {
		ch <- store.Event{0, path, v[0], rev, "", nil, nil}
		return
	}
	if path == "/" {
		path = ""
	}
	for _, ent := range v {
		walk(path+"/"+ent, st, ch)
	}
}

func activate(st *store.Store, self string, c *client.Client, cal chan int) {
	logger := util.NewLogger("activate")
	ch := make(chan store.Event)
	st.GetDirAndWatch("/doozer/slot", ch)
	for ev := range ch {
		// TODO ev.IsEmpty()
		if ev.IsSet() && ev.Body == "" {
			_, err := c.Set(ev.Path, self, ev.Cas)
			if err != nil {
				logger.Println(err)
				continue
			}
			close(cal)
			close(ch)
		}
	}
}

func sendLearn(out chan<- Packet, p *packet, st *store.Store) {
	if p.msg.Cmd != nil && *p.msg.Cmd == msg_INVITE {
		ch, err := st.Wait(store.Any, *p.Seqn)

		if err == store.ErrTooLate {
			log.Println(err)
		} else {
			e := <-ch
			m := msg{
				Seqn:  &e.Seqn,
				Cmd:   learn,
				Value: []byte(e.Mut),
			}
			buf, _ := proto.Marshal(&m)
			out <- Packet{p.Addr, buf}
		}
	}
}

func Clean(st *store.Store, pp paxos.Proposer) {
	logger := util.NewLogger("lock")
	for ev := range st.Watch("/session/*") {
		if !ev.IsDel() {
			continue
		}

		parts := strings.Split(ev.Path, "/", 3)
		name := parts[2]
		logger.Printf("lost session %s", name)

		ch, err := store.Walk(ev, "/lock/**")
		if err != nil {
			continue
		}

		for ev := range ch {
			if ev.Body == name {
				paxos.Del(pp, ev.Path, ev.Cas)
			}
		}
	}
}

func generateRuns(rev, alpha int64, st *store.Store, runs chan<- *run, t run) {
	for {
		ch, err := st.Wait(store.Any, rev)
		if err != nil {
			panic(err) // can't happen
		}

		e := <-ch
		if closed(ch) {
			break
		}
		rev = e.Seqn + 1

		r := t
		r.seqn = e.Seqn + alpha
		r.cals = getCals(e)
		r.addrs = getAddrs(e)
		r.c.size = len(r.cals)
		r.c.quor = r.quorum()
		r.c.crnd = r.indexOf(r.self) + int64(len(r.cals))
		r.l.init(int64(r.quorum()))
		runs <- &r
	}
}

func activate(st *store.Store, self string, c *doozer.Conn) int64 {
	rev, _ := st.Snap()

	for _, base := range store.Getdir(st, calDir) {
		p := calDir + "/" + base
		v, rev := st.Get(p)
		if rev != store.Dir && v[0] == "" {
			seqn, err := c.Set(p, rev, []byte(self))
			if err != nil {
				log.Println(err)
				continue
			}

			return seqn
		}
	}

	for {
		ch, err := st.Wait(calGlob, rev+1)
		if err != nil {
			panic(err)
		}
		ev, ok := <-ch
		if !ok {
			panic(os.EOF)
		}
		rev = ev.Rev
		// TODO ev.IsEmpty()
		if ev.IsSet() && ev.Body == "" {
			seqn, err := c.Set(ev.Path, ev.Rev, []byte(self))
			if err != nil {
				log.Println(err)
				continue
			}
			return seqn
		} else if ev.IsSet() && ev.Body == self {
			return ev.Seqn
		}
	}

	return 0
}

func Monitor(self string, st *store.Store, cl SetDeler) os.Error {

	mon := &monitor{
		self:    self,
		st:      st,
		cl:      cl,
		clock:   make(chan ticker),
		units:   make(map[string]unit),
		refs:    make(map[string]int),
		exitCh:  make(chan exit),
		readyCh: make(chan ready),
		logger:  util.NewLogger("monitor"),
	}

	mon.logger.Println("reading units")
	evs := make(chan store.Event)
	st.GetDirAndWatch(ctlKey, evs)
	go func(c <-chan store.Event) {
		for e := range c {
			evs <- e
		}
		close(evs)
	}(st.Watch(lockKey + "/*"))

	for {
		select {
		case t := <-mon.clock:
			t.tick()
		case ev := <-evs:
			prefix, id := path.Split(ev.Path)
			switch prefix {
			case ctlDir:
				if ev.IsDel() {
					mon.logger.Println("\n\n\ndel", id)
					mon.decrefUnit(id)
					break
				}

				ut := mon.increfUnit(id)
				if ut == nil {
					break
				}

				switch ev.Body {
				case "start":
					ut.start()
				case "stop":
					ut.stop()
				case "auto", "":
					fallthrough
				default:
					// nothing
				}

			case lockDir:
				ut := mon.units[id]
				if ut == nil {
					break
				}

				ut.dispatchLockEvent(ev)
			}
		case e := <-mon.exitCh:
			e.e.exited(e.w)
		case r := <-mon.readyCh:
			r.r.ready(r.f)
		}
	}
	panic("unreachable")
}

func Clean(st *store.Store, keep int64, ticker <-chan time.Time) {
	for _ = range ticker {
		last := (<-st.Seqns) - keep
		st.Clean(last)
	}
}