// Copyright 2016 The etcd Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package v3rpc

import (
	"sync"
	"time"

	"github.com/coreos/etcd/etcdserver"
	"github.com/coreos/etcd/etcdserver/api"
	"github.com/coreos/etcd/etcdserver/api/v3rpc/rpctypes"
	"github.com/coreos/etcd/pkg/types"
	"github.com/coreos/etcd/raft"

	prometheus "github.com/grpc-ecosystem/go-grpc-prometheus"
	"golang.org/x/net/context"
	"google.golang.org/grpc"
	"google.golang.org/grpc/metadata"
)

const (
	maxNoLeaderCnt = 3
)

type streamsMap struct {
	mu      sync.Mutex
	streams map[grpc.ServerStream]struct{}
}

func newUnaryInterceptor(s *etcdserver.EtcdServer) grpc.UnaryServerInterceptor {
	return func(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (resp interface{}, err error) {
		if !api.IsCapabilityEnabled(api.V3rpcCapability) {
			return nil, rpctypes.ErrGRPCNotCapable
		}

		md, ok := metadata.FromContext(ctx)
		if ok {
			if ks := md[rpctypes.MetadataRequireLeaderKey]; len(ks) > 0 && ks[0] == rpctypes.MetadataHasLeader {
				if s.Leader() == types.ID(raft.None) {
					return nil, rpctypes.ErrGRPCNoLeader
				}
			}
		}

		return prometheus.UnaryServerInterceptor(ctx, req, info, handler)
	}
}

func newStreamInterceptor(s *etcdserver.EtcdServer) grpc.StreamServerInterceptor {
	smap := monitorLeader(s)

	return func(srv interface{}, ss grpc.ServerStream, info *grpc.StreamServerInfo, handler grpc.StreamHandler) error {
		if !api.IsCapabilityEnabled(api.V3rpcCapability) {
			return rpctypes.ErrGRPCNotCapable
		}

		md, ok := metadata.FromContext(ss.Context())
		if ok {
			if ks := md[rpctypes.MetadataRequireLeaderKey]; len(ks) > 0 && ks[0] == rpctypes.MetadataHasLeader {
				if s.Leader() == types.ID(raft.None) {
					return rpctypes.ErrGRPCNoLeader
				}

				cctx, cancel := context.WithCancel(ss.Context())
				ss = serverStreamWithCtx{ctx: cctx, cancel: &cancel, ServerStream: ss}

				smap.mu.Lock()
				smap.streams[ss] = struct{}{}
				smap.mu.Unlock()

				defer func() {
					smap.mu.Lock()
					delete(smap.streams, ss)
					smap.mu.Unlock()
					cancel()
				}()

			}
		}

		return prometheus.StreamServerInterceptor(srv, ss, info, handler)
	}
}

type serverStreamWithCtx struct {
	grpc.ServerStream
	ctx    context.Context
	cancel *context.CancelFunc
}

func (ssc serverStreamWithCtx) Context() context.Context { return ssc.ctx }

func monitorLeader(s *etcdserver.EtcdServer) *streamsMap {
	smap := &streamsMap{
		streams: make(map[grpc.ServerStream]struct{}),
	}

	go func() {
		election := time.Duration(s.Cfg.TickMs) * time.Duration(s.Cfg.ElectionTicks) * time.Millisecond
		noLeaderCnt := 0

		for {
			select {
			case <-s.StopNotify():
				return
			case <-time.After(election):
				if s.Leader() == types.ID(raft.None) {
					noLeaderCnt++
				} else {
					noLeaderCnt = 0
				}

				// We are more conservative on canceling existing streams. Reconnecting streams
				// cost much more than just rejecting new requests. So we wait until the member
				// cannot find a leader for maxNoLeaderCnt election timeouts to cancel existing streams.
				if noLeaderCnt >= maxNoLeaderCnt {
					smap.mu.Lock()
					for ss := range smap.streams {
						if ssWithCtx, ok := ss.(serverStreamWithCtx); ok {
							(*ssWithCtx.cancel)()
							<-ss.Context().Done()
						}
					}
					smap.streams = make(map[grpc.ServerStream]struct{})
					smap.mu.Unlock()
				}
			}
		}
	}()

	return smap
}
