// wait blocks until it can receive from ctx.Done, closing, or proceed.
// If it receives from ctx.Done, it returns 0, the StreamError for ctx.Err.
// If it receives from closing, it returns 0, ErrConnClosing.
// If it receives from proceed, it returns the received integer, nil.
func wait(ctx context.Context, closing <-chan struct{}, proceed <-chan int) (int, error) {
	select {
	case <-ctx.Done():
		return 0, ContextErr(ctx.Err())
	case <-closing:
		return 0, ErrConnClosing
	case i := <-proceed:
		return i, nil
	}
}

func (mn *multiNode) step(ctx context.Context, m multiMessage) error {
	ch := mn.recvc
	if m.msg.Type == pb.MsgProp {
		ch = mn.propc
	}

	select {
	case ch <- m:
		return nil
	case <-ctx.Done():
		return ctx.Err()
	case <-mn.done:
		return ErrStopped
	}
}

func (c *httpClusterClient) AutoSync(ctx context.Context, interval time.Duration) error {
	ticker := time.NewTicker(interval)
	defer ticker.Stop()
	for {
		err := c.Sync(ctx)
		if err != nil {
			return err
		}
		select {
		case <-ctx.Done():
			return ctx.Err()
		case <-ticker.C:
		}
	}
}

func contextClient(ctx context.Context) (*http.Client, error) {
	for _, fn := range contextClientFuncs {
		c, err := fn(ctx)
		if err != nil {
			return nil, err
		}
		if c != nil {
			return c, nil
		}
	}
	if hc, ok := ctx.Value(HTTPClient).(*http.Client); ok {
		return hc, nil
	}
	return http.DefaultClient, nil
}

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()
		}
	}
}

func (s *EtcdServer) V3DemoDo(ctx context.Context, r pb.InternalRaftRequest) (proto.Message, error) {
	r.ID = s.reqIDGen.Next()

	data, err := r.Marshal()
	if err != nil {
		return &pb.EmptyResponse{}, err
	}
	ch := s.w.Register(r.ID)

	s.r.Propose(ctx, data)

	select {
	case x := <-ch:
		result := x.(*applyResult)
		return result.resp, result.err
	case <-ctx.Done():
		s.w.Trigger(r.ID, nil) // GC wait
		return &pb.EmptyResponse{}, ctx.Err()
	case <-s.done:
		return &pb.EmptyResponse{}, ErrStopped
	}
}

// FromContext returns the MD in ctx if it exists.
func FromContext(ctx context.Context) (md MD, ok bool) {
	md, ok = ctx.Value(mdKey{}).(MD)
	return
}

func (c *simpleHTTPClient) Do(ctx context.Context, act httpAction) (*http.Response, []byte, error) {
	req := act.HTTPRequest(c.endpoint)

	if err := printcURL(req); err != nil {
		return nil, nil, err
	}

	hctx, hcancel := context.WithCancel(ctx)
	if c.headerTimeout > 0 {
		hctx, hcancel = context.WithTimeout(ctx, c.headerTimeout)
	}
	defer hcancel()

	reqcancel := requestCanceler(c.transport, req)

	rtchan := make(chan roundTripResponse, 1)
	go func() {
		resp, err := c.transport.RoundTrip(req)
		rtchan <- roundTripResponse{resp: resp, err: err}
		close(rtchan)
	}()

	var resp *http.Response
	var err error

	select {
	case rtresp := <-rtchan:
		resp, err = rtresp.resp, rtresp.err
	case <-hctx.Done():
		// cancel and wait for request to actually exit before continuing
		reqcancel()
		rtresp := <-rtchan
		resp = rtresp.resp
		switch {
		case ctx.Err() != nil:
			err = ctx.Err()
		case hctx.Err() != nil:
			err = fmt.Errorf("client: endpoint %s exceeded header timeout", c.endpoint.String())
		default:
			panic("failed to get error from context")
		}
	}

	// always check for resp nil-ness to deal with possible
	// race conditions between channels above
	defer func() {
		if resp != nil {
			resp.Body.Close()
		}
	}()

	if err != nil {
		return nil, nil, err
	}

	var body []byte
	done := make(chan struct{})
	go func() {
		body, err = ioutil.ReadAll(resp.Body)
		done <- struct{}{}
	}()

	select {
	case <-ctx.Done():
		resp.Body.Close()
		<-done
		return nil, nil, ctx.Err()
	case <-done:
	}

	return resp, body, err
}

// StreamFromContext returns the stream saved in ctx.
func StreamFromContext(ctx context.Context) (s *Stream, ok bool) {
	s, ok = ctx.Value(streamKey).(*Stream)
	return
}

// cc returns the internal *cloudContext (cc) state for a context.Context.
// It panics if the user did it wrong.
func cc(ctx context.Context) *cloudContext {
	if c, ok := ctx.Value(contextKey{}).(*cloudContext); ok {
		return c
	}
	panic("invalid context.Context type; it should be created with cloud.NewContext")
}

// NewStream creates a stream and register it into the transport as "active"
// streams.
func (t *http2Client) NewStream(ctx context.Context, callHdr *CallHdr) (_ *Stream, err error) {
	// Record the timeout value on the context.
	var timeout time.Duration
	if dl, ok := ctx.Deadline(); ok {
		timeout = dl.Sub(time.Now())
		if timeout <= 0 {
			return nil, ContextErr(context.DeadlineExceeded)
		}
	}
	authData := make(map[string]string)
	for _, c := range t.authCreds {
		data, err := c.GetRequestMetadata(ctx)
		if err != nil {
			return nil, StreamErrorf(codes.InvalidArgument, "transport: %v", err)
		}
		for k, v := range data {
			authData[k] = v
		}
	}
	if _, err := wait(ctx, t.shutdownChan, t.writableChan); err != nil {
		return nil, err
	}
	t.mu.Lock()
	if t.state != reachable {
		t.mu.Unlock()
		return nil, ErrConnClosing
	}
	if uint32(len(t.activeStreams)) >= t.maxStreams {
		t.mu.Unlock()
		t.writableChan <- 0
		return nil, StreamErrorf(codes.Unavailable, "transport: failed to create new stream because the limit has been reached.")
	}
	s := t.newStream(ctx, callHdr)
	t.activeStreams[s.id] = s
	t.mu.Unlock()
	// HPACK encodes various headers. Note that once WriteField(...) is
	// called, the corresponding headers/continuation frame has to be sent
	// because hpack.Encoder is stateful.
	t.hBuf.Reset()
	t.hEnc.WriteField(hpack.HeaderField{Name: ":method", Value: "POST"})
	t.hEnc.WriteField(hpack.HeaderField{Name: ":scheme", Value: t.scheme})
	t.hEnc.WriteField(hpack.HeaderField{Name: ":path", Value: callHdr.Method})
	t.hEnc.WriteField(hpack.HeaderField{Name: ":authority", Value: callHdr.Host})
	t.hEnc.WriteField(hpack.HeaderField{Name: "content-type", Value: "application/grpc"})
	t.hEnc.WriteField(hpack.HeaderField{Name: "te", Value: "trailers"})
	if timeout > 0 {
		t.hEnc.WriteField(hpack.HeaderField{Name: "grpc-timeout", Value: timeoutEncode(timeout)})
	}
	for k, v := range authData {
		t.hEnc.WriteField(hpack.HeaderField{Name: k, Value: v})
	}
	var (
		hasMD      bool
		endHeaders bool
	)
	if md, ok := metadata.FromContext(ctx); ok {
		hasMD = true
		for k, v := range md {
			t.hEnc.WriteField(hpack.HeaderField{Name: k, Value: v})
		}
	}
	first := true
	// Sends the headers in a single batch even when they span multiple frames.
	for !endHeaders {
		size := t.hBuf.Len()
		if size > http2MaxFrameLen {
			size = http2MaxFrameLen
		} else {
			endHeaders = true
		}
		if first {
			// Sends a HeadersFrame to server to start a new stream.
			p := http2.HeadersFrameParam{
				StreamID:      s.id,
				BlockFragment: t.hBuf.Next(size),
				EndStream:     false,
				EndHeaders:    endHeaders,
			}
			// Do a force flush for the buffered frames iff it is the last headers frame
			// and there is header metadata to be sent. Otherwise, there is flushing until
			// the corresponding data frame is written.
			err = t.framer.writeHeaders(hasMD && endHeaders, p)
			first = false
		} else {
			// Sends Continuation frames for the leftover headers.
			err = t.framer.writeContinuation(hasMD && endHeaders, s.id, endHeaders, t.hBuf.Next(size))
		}
		if err != nil {
			t.notifyError(err)
			return nil, ConnectionErrorf("transport: %v", err)
		}
	}
	t.writableChan <- 0
	return s, nil
}