// writeEvent serializes a single Event and writes the resulting
// JSON to the given ResponseWriter, along with the appropriate
// headers
func writeEvent(w http.ResponseWriter, ev *store.Event, rt etcdserver.RaftTimer) error {
	if ev == nil {
		return errors.New("cannot write empty Event!")
	}
	w.Header().Set("Content-Type", "application/json")
	w.Header().Set("X-Etcd-Index", fmt.Sprint(ev.EtcdIndex))
	w.Header().Set("X-Raft-Index", fmt.Sprint(rt.Index()))
	w.Header().Set("X-Raft-Term", fmt.Sprint(rt.Term()))

	if ev.IsCreated() {
		w.WriteHeader(http.StatusCreated)
	}

	return json.NewEncoder(w).Encode(ev)
}

func handleKeyWatch(ctx context.Context, w http.ResponseWriter, wa store.Watcher, stream bool, rt etcdserver.RaftTimer) {
	defer wa.Remove()
	ech := wa.EventChan()
	var nch <-chan bool
	if x, ok := w.(http.CloseNotifier); ok {
		nch = x.CloseNotify()
	}

	w.Header().Set("Content-Type", "application/json")
	w.Header().Set("X-Etcd-Index", fmt.Sprint(wa.StartIndex()))
	w.Header().Set("X-Raft-Index", fmt.Sprint(rt.Index()))
	w.Header().Set("X-Raft-Term", fmt.Sprint(rt.Term()))
	w.WriteHeader(http.StatusOK)

	// Ensure headers are flushed early, in case of long polling
	w.(http.Flusher).Flush()

	for {
		select {
		case <-nch:
			// Client closed connection. Nothing to do.
			return
		case <-ctx.Done():
			// Timed out. net/http will close the connection for us, so nothing to do.
			return
		case ev, ok := <-ech:
			if !ok {
				// If the channel is closed this may be an indication of
				// that notifications are much more than we are able to
				// send to the client in time. Then we simply end streaming.
				return
			}
			ev = trimEventPrefix(ev, etcdserver.StoreKeysPrefix)
			if err := json.NewEncoder(w).Encode(ev); err != nil {
				// Should never be reached
				plog.Warningf("error writing event (%v)", err)
				return
			}
			if !stream {
				return
			}
			w.(http.Flusher).Flush()
		}
	}
}

// writeKeyEvent trims the prefix of key path in a single Event under
// StoreKeysPrefix, serializes it and writes the resulting JSON to the given
// ResponseWriter, along with the appropriate headers.
func writeKeyEvent(w http.ResponseWriter, ev *store.Event, noValueOnSuccess bool, rt etcdserver.RaftTimer) error {
	if ev == nil {
		return errors.New("cannot write empty Event!")
	}
	w.Header().Set("Content-Type", "application/json")
	w.Header().Set("X-Etcd-Index", fmt.Sprint(ev.EtcdIndex))
	w.Header().Set("X-Raft-Index", fmt.Sprint(rt.Index()))
	w.Header().Set("X-Raft-Term", fmt.Sprint(rt.Term()))

	if ev.IsCreated() {
		w.WriteHeader(http.StatusCreated)
	}

	ev = trimEventPrefix(ev, etcdserver.StoreKeysPrefix)
	if noValueOnSuccess &&
		(ev.Action == store.Set || ev.Action == store.CompareAndSwap ||
			ev.Action == store.Create || ev.Action == store.Update) {
		ev.Node = nil
		ev.PrevNode = nil
	}
	return json.NewEncoder(w).Encode(ev)
}