// Copyright (C) 2019-2020 Zilliz. All rights reserved.
//
// 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 datanode implements data persistence logic.
//
// Data node persists insert logs into persistent storage like minIO/S3.
package datanode

import (
	"context"
	"errors"
	"fmt"
	"io"
	"math/rand"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	clientv3 "go.etcd.io/etcd/client/v3"
	"go.uber.org/zap"

	"github.com/golang/protobuf/proto"
	etcdkv "github.com/milvus-io/milvus/internal/kv/etcd"
	"github.com/milvus-io/milvus/internal/log"
	"github.com/milvus-io/milvus/internal/logutil"
	"github.com/milvus-io/milvus/internal/metrics"
	"github.com/milvus-io/milvus/internal/msgstream"
	"github.com/milvus-io/milvus/internal/types"
	"github.com/milvus-io/milvus/internal/util/metricsinfo"
	"github.com/milvus-io/milvus/internal/util/retry"
	"github.com/milvus-io/milvus/internal/util/sessionutil"
	"github.com/milvus-io/milvus/internal/util/typeutil"

	"github.com/milvus-io/milvus/internal/proto/commonpb"
	"github.com/milvus-io/milvus/internal/proto/datapb"
	"github.com/milvus-io/milvus/internal/proto/internalpb"
	"github.com/milvus-io/milvus/internal/proto/milvuspb"
	"github.com/milvus-io/milvus/internal/proto/rootcoordpb"
)

const (
	RPCConnectionTimeout = 30 * time.Second

	// MetricRequestsTotal used to count the num of total requests
	MetricRequestsTotal = "total"

	// MetricRequestsSuccess used to count the num of successful requests
	MetricRequestsSuccess = "success"

	// ConnectEtcdMaxRetryTime used to limit the max retry time for connection etcd
	ConnectEtcdMaxRetryTime = 1000
)

const illegalRequestErrStr = "Illegal request"

// DataNode communicates with outside services and unioun all
// services in datanode package.
//
// DataNode implements `types.Component`, `types.DataNode` interfaces.
//  `rootCoord` is a grpc client of root coordinator.
//  `dataCoord` is a grpc client of data service.
//  `NodeID` is unique to each datanode.
//  `State` is current statement of this data node, indicating whether it's healthy.
//
//  `vchan2SyncService` is a map of vchannlName to dataSyncService, so that datanode
//  has ability to scale flowgraph.
//  `vchan2FlushCh` holds flush-signal channels for every flowgraph.

//  `clearSignal` is a signal channel for releasing the flowgraph resources.
//  `segmentCache` stores all flushing and flushed segments.
type DataNode struct {
	ctx    context.Context
	cancel context.CancelFunc
	NodeID UniqueID
	Role   string
	State  atomic.Value // internalpb.StateCode_Initializing

	chanMut           sync.RWMutex
	vchan2SyncService map[string]*dataSyncService // vchannel name
	vchan2FlushCh     map[string]chan<- *flushMsg // vchannel name
	clearSignal       chan UniqueID               // collection ID
	segmentCache      *Cache

	rootCoord types.RootCoord
	dataCoord types.DataCoord

	session  *sessionutil.Session
	kvClient *etcdkv.EtcdKV

	closer io.Closer

	msFactory msgstream.Factory
}

// NewDataNode will return a DataNode with abnormal state.
func NewDataNode(ctx context.Context, factory msgstream.Factory) *DataNode {
	rand.Seed(time.Now().UnixNano())
	ctx2, cancel2 := context.WithCancel(ctx)
	node := &DataNode{
		ctx:    ctx2,
		cancel: cancel2,
		Role:   typeutil.DataNodeRole,

		rootCoord:    nil,
		dataCoord:    nil,
		msFactory:    factory,
		segmentCache: newCache(),

		vchan2SyncService: make(map[string]*dataSyncService),
		vchan2FlushCh:     make(map[string]chan<- *flushMsg),
		clearSignal:       make(chan UniqueID, 100),
	}
	node.UpdateStateCode(internalpb.StateCode_Abnormal)
	return node
}

// SetRootCoordInterface sets RootCoord's grpc client, error is returned if repeatedly set.
func (node *DataNode) SetRootCoordInterface(rc types.RootCoord) error {
	switch {
	case rc == nil, node.rootCoord != nil:
		return errors.New("Nil parameter or repeatly set")
	default:
		node.rootCoord = rc
		return nil
	}
}

// SetDataCoordInterface sets data service's grpc client, error is returned if repeatedly set.
func (node *DataNode) SetDataCoordInterface(ds types.DataCoord) error {
	switch {
	case ds == nil, node.dataCoord != nil:
		return errors.New("Nil parameter or repeatly set")
	default:
		node.dataCoord = ds
		return nil
	}
}

// Register register datanode to etcd
func (node *DataNode) Register() error {
	node.session = sessionutil.NewSession(node.ctx, Params.MetaRootPath, Params.EtcdEndpoints)
	node.session.Init(typeutil.DataNodeRole, Params.IP+":"+strconv.Itoa(Params.Port), false)
	Params.NodeID = node.session.ServerID
	node.NodeID = node.session.ServerID
	// Start node watch node
	go node.StartWatchChannels(node.ctx)

	Params.initMsgChannelSubName()
	log.Debug("DataNode Init",
		zap.String("MsgChannelSubName", Params.MsgChannelSubName),
	)
	return nil
}

// Init function do nothing now.
func (node *DataNode) Init() error {
	log.Debug("DataNode Init",
		zap.String("SegmentStatisticsChannelName", Params.SegmentStatisticsChannelName),
		zap.String("TimeTickChannelName", Params.TimeTickChannelName),
	)

	return nil
}

// StartWatchChannels start loop to watch channel allocation status via kv(etcd for now)
func (node *DataNode) StartWatchChannels(ctx context.Context) {
	defer logutil.LogPanic()
	// REF MEP#7 watch path should be [prefix]/channel/{node_id}/{channel_name}
	watchPrefix := fmt.Sprintf("channel/%d", node.NodeID)
	evtChan := node.kvClient.WatchWithPrefix(watchPrefix)
	for {
		select {
		case <-ctx.Done():
			log.Debug("watch etcd loop quit")
			return
		case event := <-evtChan:
			if event.Canceled { // failed to watch
				log.Warn("Watch channel failed", zap.Error(event.Err()))
				// if watch loop return due to event canceled, the datanode is not functional anymore
				// stop the datanode and wait for restart
				node.Stop()
				return
			}
			for _, evt := range event.Events {
				go node.handleChannelEvt(evt)
			}
		}
	}
}

// handleChannelEvt handles event from kv watch event
func (node *DataNode) handleChannelEvt(evt *clientv3.Event) {
	switch evt.Type {
	case clientv3.EventTypePut: // datacoord shall put channels needs to be watched here
		watchInfo := datapb.ChannelWatchInfo{}
		err := proto.Unmarshal(evt.Kv.Value, &watchInfo)
		if err != nil {
			log.Warn("fail to parse ChannelWatchInfo", zap.String("key", string(evt.Kv.Key)), zap.Error(err))
			return
		}
		if watchInfo.State == datapb.ChannelWatchState_Complete {
			return
		}
		if watchInfo.Vchan == nil {
			log.Warn("found ChannelWatchInfo with nil VChannelInfo", zap.String("key", string(evt.Kv.Key)))
			return
		}
		err = node.NewDataSyncService(watchInfo.Vchan)
		if err != nil {
			log.Warn("fail to create DataSyncService", zap.String("key", string(evt.Kv.Key)), zap.Error(err))
			return
		}
		watchInfo.State = datapb.ChannelWatchState_Complete
		v, _ := proto.Marshal(&watchInfo)
		err = node.kvClient.Save(fmt.Sprintf("channel/%d/%s", node.NodeID, watchInfo.Vchan.ChannelName), string(v))
		if err != nil {
			log.Warn("fail to change WatchState to complete", zap.String("key", string(evt.Kv.Key)), zap.Error(err))
			node.ReleaseDataSyncService(string(evt.Kv.Key))
			// TODO GOOSE: maybe retry logic and exit logic
		}
	case clientv3.EventTypeDelete:
		// guaranteed there is no "/" in channel name
		parts := strings.Split(string(evt.Kv.Key), "/")
		node.ReleaseDataSyncService(parts[len(parts)-1])
	}
}

// NewDataSyncService adds a new dataSyncService for new dmlVchannel and starts dataSyncService.
func (node *DataNode) NewDataSyncService(vchan *datapb.VchannelInfo) error {
	node.chanMut.Lock()
	defer node.chanMut.Unlock()
	if _, ok := node.vchan2SyncService[vchan.GetChannelName()]; ok {
		return nil
	}

	replica := newReplica(node.rootCoord, vchan.CollectionID)

	var alloc allocatorInterface = newAllocator(node.rootCoord)

	log.Debug("Received Vchannel Info",
		zap.Int("Unflushed Segment Number", len(vchan.GetUnflushedSegments())),
		zap.Int("Flushed Segment Number", len(vchan.GetFlushedSegments())),
	)

	flushChan := make(chan *flushMsg, 100)
	dataSyncService, err := newDataSyncService(node.ctx, flushChan, replica, alloc, node.msFactory, vchan, node.clearSignal, node.dataCoord)
	if err != nil {
		return err
	}

	node.vchan2SyncService[vchan.GetChannelName()] = dataSyncService
	node.vchan2FlushCh[vchan.GetChannelName()] = flushChan

	log.Info("Start New dataSyncService",
		zap.Int64("Collection ID", vchan.GetCollectionID()),
		zap.String("Vchannel name", vchan.GetChannelName()),
	)
	go dataSyncService.start()

	return nil
}

// BackGroundGC runs in background to release datanode resources
func (node *DataNode) BackGroundGC(collIDCh <-chan UniqueID) {
	log.Info("DataNode Background GC Start")
	for {
		select {
		case collID := <-collIDCh:
			log.Info("GC collection", zap.Int64("ID", collID))
			for _, vchanName := range node.getChannelNamesbyCollectionID(collID) {
				node.ReleaseDataSyncService(vchanName)
			}
		case <-node.ctx.Done():
			log.Info("DataNode ctx done")
			return
		}
	}
}

// ReleaseDataSyncService release flowgraph resources for a vchanName
func (node *DataNode) ReleaseDataSyncService(vchanName string) {
	log.Info("Release flowgraph resources begin", zap.String("Vchannel", vchanName))

	node.chanMut.Lock()
	defer node.chanMut.Unlock()
	if dss, ok := node.vchan2SyncService[vchanName]; ok {
		dss.close()
	}

	delete(node.vchan2SyncService, vchanName)
	delete(node.vchan2FlushCh, vchanName)

	log.Debug("Release flowgraph resources end", zap.String("Vchannel", vchanName))
}

var FilterThreshold Timestamp

// Start will update DataNode state to HEALTHY
func (node *DataNode) Start() error {

	rep, err := node.rootCoord.AllocTimestamp(node.ctx, &rootcoordpb.AllocTimestampRequest{
		Base: &commonpb.MsgBase{
			MsgType:   commonpb.MsgType_RequestTSO,
			MsgID:     0,
			Timestamp: 0,
			SourceID:  node.NodeID,
		},
		Count: 1,
	})
	if err != nil {
		log.Warn("fail to alloc timestamp", zap.Error(err))
		return err
	}

	connectEtcdFn := func() error {
		etcdKV, err := etcdkv.NewEtcdKV(Params.EtcdEndpoints, Params.MetaRootPath)
		if err != nil {
			return err
		}
		node.kvClient = etcdKV
		return nil
	}
	err = retry.Do(node.ctx, connectEtcdFn, retry.Attempts(ConnectEtcdMaxRetryTime))
	if err != nil {
		return errors.New("DataNode fail to connect etcd")
	}

	if rep.Status.ErrorCode != commonpb.ErrorCode_Success || err != nil {
		return errors.New("DataNode fail to start")
	}

	FilterThreshold = rep.GetTimestamp()

	go node.BackGroundGC(node.clearSignal)
	node.UpdateStateCode(internalpb.StateCode_Healthy)
	return nil
}

// UpdateStateCode updates datanode's state code
func (node *DataNode) UpdateStateCode(code internalpb.StateCode) {
	node.State.Store(code)
}

func (node *DataNode) isHealthy() bool {
	code := node.State.Load().(internalpb.StateCode)
	return code == internalpb.StateCode_Healthy
}

// WatchDmChannels create a new dataSyncService for every unique dmlVchannel name, ignore if dmlVchannel existed.
func (node *DataNode) WatchDmChannels(ctx context.Context, in *datapb.WatchDmChannelsRequest) (*commonpb.Status, error) {
	metrics.DataNodeWatchDmChannelsCounter.WithLabelValues(MetricRequestsTotal).Inc()
	status := &commonpb.Status{
		ErrorCode: commonpb.ErrorCode_UnexpectedError,
	}

	switch {
	case !node.isHealthy():
		status.Reason = msgDataNodeIsUnhealthy(node.NodeID)
		return status, nil

	case len(in.GetVchannels()) == 0:
		status.Reason = illegalRequestErrStr
		return status, nil

	default:
		for _, chanInfo := range in.GetVchannels() {
			log.Info("DataNode new dataSyncService",
				zap.String("channel name", chanInfo.ChannelName),
				zap.Any("channal Info", chanInfo),
			)
			if err := node.NewDataSyncService(chanInfo); err != nil {
				log.Warn("Failed to new data sync service", zap.Any("channel", chanInfo))
			}
		}

		status.ErrorCode = commonpb.ErrorCode_Success
		log.Debug("DataNode WatchDmChannels Done")
		metrics.DataNodeWatchDmChannelsCounter.WithLabelValues(MetricRequestsSuccess).Inc()
		return status, nil
	}
}

// GetComponentStates will return current state of DataNode
func (node *DataNode) GetComponentStates(ctx context.Context) (*internalpb.ComponentStates, error) {
	log.Debug("DataNode current state", zap.Any("State", node.State.Load()))
	states := &internalpb.ComponentStates{
		State: &internalpb.ComponentInfo{
			NodeID:    Params.NodeID,
			Role:      node.Role,
			StateCode: node.State.Load().(internalpb.StateCode),
		},
		SubcomponentStates: make([]*internalpb.ComponentInfo, 0),
		Status:             &commonpb.Status{ErrorCode: commonpb.ErrorCode_Success},
	}
	return states, nil
}

func (node *DataNode) getChannelNamebySegmentID(segID UniqueID) string {
	node.chanMut.RLock()
	defer node.chanMut.RUnlock()
	for name, dataSync := range node.vchan2SyncService {
		if dataSync.replica.hasSegment(segID, false) {
			return name
		}
	}
	return ""
}

func (node *DataNode) getChannelNamesbyCollectionID(collID UniqueID) []string {
	node.chanMut.RLock()
	defer node.chanMut.RUnlock()

	channels := make([]string, 0, len(node.vchan2SyncService))
	for name, dataSync := range node.vchan2SyncService {
		if dataSync.collectionID == collID {
			channels = append(channels, name)
		}
	}
	return channels
}

// ReadyToFlush tells wether DataNode is ready for flushing
func (node *DataNode) ReadyToFlush() error {
	if node.State.Load().(internalpb.StateCode) != internalpb.StateCode_Healthy {
		return errors.New("DataNode not in HEALTHY state")
	}

	node.chanMut.RLock()
	defer node.chanMut.RUnlock()
	if len(node.vchan2SyncService) == 0 && len(node.vchan2FlushCh) == 0 {
		// Healthy but Idle
		msg := "DataNode HEALTHY but IDLE, please try WatchDmChannels to make it work"
		log.Warn(msg)
		return errors.New(msg)
	}

	if len(node.vchan2SyncService) != len(node.vchan2FlushCh) {
		// TODO restart
		msg := "DataNode HEALTHY but abnormal inside, restarting..."
		log.Warn(msg)
		return errors.New(msg)
	}
	return nil
}

// FlushSegments packs flush messages into flowgraph through flushChan.
//   If DataNode receives a valid segment to flush, new flush message for the segment should be ignored.
//   So if receiving calls to flush segment A, DataNode should guarantee the segment to be flushed.
//
//   There are 1 precondition: The segmentID in req is in ascending order.
func (node *DataNode) FlushSegments(ctx context.Context, req *datapb.FlushSegmentsRequest) (*commonpb.Status, error) {
	metrics.DataNodeFlushSegmentsCounter.WithLabelValues(MetricRequestsTotal).Inc()
	status := &commonpb.Status{
		ErrorCode: commonpb.ErrorCode_UnexpectedError,
	}

	if err := node.ReadyToFlush(); err != nil {
		status.Reason = err.Error()
		return status, nil
	}

	numOfFlushingSeg := len(req.SegmentIDs)
	log.Debug("FlushSegments ...",
		zap.Int("num", len(req.SegmentIDs)),
		zap.Int64s("segments", req.SegmentIDs),
	)

	dmlFlushedCh := make(chan []*datapb.FieldBinlog, len(req.SegmentIDs))
	for _, id := range req.SegmentIDs {
		chanName := node.getChannelNamebySegmentID(id)
		log.Debug("vchannel",
			zap.String("name", chanName),
			zap.Int64("SegmentID", id))

		if len(chanName) == 0 {
			status.Reason = fmt.Sprintf("DataNode not find segment %d!", id)
			return status, nil
		}

		if node.segmentCache.checkIfCached(id) {
			// Segment in flushing or flushed, ignore
			log.Info("Segment in flushing, ignore it", zap.Int64("ID", id))
			numOfFlushingSeg--
			continue
		}

		node.segmentCache.Cache(id)

		node.chanMut.RLock()
		flushCh, ok := node.vchan2FlushCh[chanName]
		node.chanMut.RUnlock()
		if !ok {
			// TODO restart DataNode or reshape vchan2FlushCh and vchan2SyncService
			status.Reason = "DataNode abnormal, restarting"
			return status, nil
		}

		flushmsg := &flushMsg{
			msgID:        req.Base.MsgID,
			timestamp:    req.Base.Timestamp,
			segmentID:    id,
			collectionID: req.CollectionID,
			dmlFlushedCh: dmlFlushedCh,
		}
		flushCh <- flushmsg

	}

	failedSegments := ""
	for i := 0; i < numOfFlushingSeg; i++ {
		msg := <-dmlFlushedCh
		if len(msg) != 1 {
			panic("flush size expect to 1")
		}
		if msg[0].Binlogs == nil {
			failedSegments += fmt.Sprintf(" %d", msg[0].FieldID)
		}
	}
	if len(failedSegments) != 0 {
		status.Reason = fmt.Sprintf("flush failed segment list = %s", failedSegments)
		return status, nil
	}

	node.segmentCache.Remove(req.SegmentIDs...)
	log.Debug("FlushSegments Done",
		zap.Int64s("segments", req.SegmentIDs))

	status.ErrorCode = commonpb.ErrorCode_Success
	metrics.DataNodeFlushSegmentsCounter.WithLabelValues(MetricRequestsSuccess).Inc()
	return status, nil
}

func (node *DataNode) Stop() error {
	node.cancel()

	node.chanMut.RLock()
	defer node.chanMut.RUnlock()
	// close services
	for _, syncService := range node.vchan2SyncService {
		if syncService != nil {
			(*syncService).close()
		}
	}

	if node.closer != nil {
		node.closer.Close()
	}
	return nil
}

func (node *DataNode) GetTimeTickChannel(ctx context.Context) (*milvuspb.StringResponse, error) {
	return &milvuspb.StringResponse{
		Status: &commonpb.Status{
			ErrorCode: commonpb.ErrorCode_Success,
			Reason:    "",
		},
		Value: "",
	}, nil
}

func (node *DataNode) GetStatisticsChannel(ctx context.Context) (*milvuspb.StringResponse, error) {
	return &milvuspb.StringResponse{
		Status: &commonpb.Status{
			ErrorCode: commonpb.ErrorCode_Success,
			Reason:    "",
		},
		Value: "",
	}, nil
}

// TODO(dragondriver): cache the Metrics and set a retention to the cache
func (node *DataNode) GetMetrics(ctx context.Context, req *milvuspb.GetMetricsRequest) (*milvuspb.GetMetricsResponse, error) {
	log.Debug("DataNode.GetMetrics",
		zap.Int64("node_id", Params.NodeID),
		zap.String("req", req.Request))

	if !node.isHealthy() {
		log.Warn("DataNode.GetMetrics failed",
			zap.Int64("node_id", Params.NodeID),
			zap.String("req", req.Request),
			zap.Error(errDataNodeIsUnhealthy(Params.NodeID)))

		return &milvuspb.GetMetricsResponse{
			Status: &commonpb.Status{
				ErrorCode: commonpb.ErrorCode_UnexpectedError,
				Reason:    msgDataNodeIsUnhealthy(Params.NodeID),
			},
			Response: "",
		}, nil
	}

	metricType, err := metricsinfo.ParseMetricType(req.Request)
	if err != nil {
		log.Warn("DataNode.GetMetrics failed to parse metric type",
			zap.Int64("node_id", Params.NodeID),
			zap.String("req", req.Request),
			zap.Error(err))

		return &milvuspb.GetMetricsResponse{
			Status: &commonpb.Status{
				ErrorCode: commonpb.ErrorCode_UnexpectedError,
				Reason:    err.Error(),
			},
			Response: "",
		}, nil
	}

	log.Debug("DataNode.GetMetrics",
		zap.String("metric_type", metricType))

	if metricType == metricsinfo.SystemInfoMetrics {
		systemInfoMetrics, err := node.getSystemInfoMetrics(ctx, req)

		log.Debug("DataNode.GetMetrics",
			zap.Int64("node_id", Params.NodeID),
			zap.String("req", req.Request),
			zap.String("metric_type", metricType),
			zap.Any("systemInfoMetrics", systemInfoMetrics), // TODO(dragondriver): necessary? may be very large
			zap.Error(err))

		return systemInfoMetrics, err
	}

	log.Debug("DataNode.GetMetrics failed, request metric type is not implemented yet",
		zap.Int64("node_id", Params.NodeID),
		zap.String("req", req.Request),
		zap.String("metric_type", metricType))

	return &milvuspb.GetMetricsResponse{
		Status: &commonpb.Status{
			ErrorCode: commonpb.ErrorCode_UnexpectedError,
			Reason:    metricsinfo.MsgUnimplementedMetric,
		},
		Response: "",
	}, nil
}