// Copyright 2017 PingCAP, Inc.
//
// 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,
// See the License for the specific language governing permissions and
// limitations under the License.

package executor

import (
	"context"
	"runtime"
	"strconv"

	"github.com/pingcap/errors"
	"github.com/pingcap/parser/model"
	"github.com/pingcap/parser/mysql"
	"github.com/pingcap/tidb/distsql"
	"github.com/pingcap/tidb/domain"
	"github.com/pingcap/tidb/metrics"
	"github.com/pingcap/tidb/sessionctx"
	"github.com/pingcap/tidb/sessionctx/variable"
	"github.com/pingcap/tidb/statistics"
	"github.com/pingcap/tidb/tablecodec"
	"github.com/pingcap/tidb/util/chunk"
	"github.com/pingcap/tidb/util/ranger"
	"github.com/pingcap/tipb/go-tipb"
	log "github.com/sirupsen/logrus"
)

var _ Executor = &AnalyzeExec{}

// AnalyzeExec represents Analyze executor.
type AnalyzeExec struct {
	baseExecutor
	tasks []*analyzeTask
}

const (
	maxSampleSize        = 10000
	maxRegionSampleSize  = 1000
	maxSketchSize        = 10000
	defaultCMSketchDepth = 5
	defaultCMSketchWidth = 2048
)

// Next implements the Executor Next interface.
func (e *AnalyzeExec) Next(ctx context.Context, req *chunk.RecordBatch) error {
	concurrency, err := getBuildStatsConcurrency(e.ctx)
	if err != nil {
		return errors.Trace(err)
	}
	taskCh := make(chan *analyzeTask, len(e.tasks))
	resultCh := make(chan statistics.AnalyzeResult, len(e.tasks))
	for i := 0; i < concurrency; i++ {
		go e.analyzeWorker(taskCh, resultCh)
	}
	for _, task := range e.tasks {
		taskCh <- task
	}
	close(taskCh)
	statsHandle := domain.GetDomain(e.ctx).StatsHandle()
	for i, panicCnt := 0, 0; i < len(e.tasks) && panicCnt < concurrency; i++ {
		result := <-resultCh
		if result.Err != nil {
			err = result.Err
			if errors.Trace(err) == errAnalyzeWorkerPanic {
				panicCnt++
			}
			log.Error(errors.ErrorStack(err))
			continue
		}
		for i, hg := range result.Hist {
			err1 := statsHandle.SaveStatsToStorage(result.PhysicalTableID, result.Count, result.IsIndex, hg, result.Cms[i], 1)
			if err1 != nil {
				err = err1
				log.Error(errors.ErrorStack(err))
				continue
			}
		}
	}
	if err != nil {
		return errors.Trace(err)
	}
	return errors.Trace(statsHandle.Update(GetInfoSchema(e.ctx)))
}

func getBuildStatsConcurrency(ctx sessionctx.Context) (int, error) {
	sessionVars := ctx.GetSessionVars()
	concurrency, err := variable.GetSessionSystemVar(sessionVars, variable.TiDBBuildStatsConcurrency)
	if err != nil {
		return 0, errors.Trace(err)
	}
	c, err := strconv.ParseInt(concurrency, 10, 64)
	return int(c), errors.Trace(err)
}

type taskType int

const (
	colTask taskType = iota
	idxTask
)

type analyzeTask struct {
	taskType taskType
	idxExec  *AnalyzeIndexExec
	colExec  *AnalyzeColumnsExec
}

var errAnalyzeWorkerPanic = errors.New("analyze worker panic")

func (e *AnalyzeExec) analyzeWorker(taskCh <-chan *analyzeTask, resultCh chan<- statistics.AnalyzeResult) {
	defer func() {
		if r := recover(); r != nil {
			buf := make([]byte, 4096)
			stackSize := runtime.Stack(buf, false)
			buf = buf[:stackSize]
			log.Errorf("analyzeWorker panic stack is:\n%s", buf)
			metrics.PanicCounter.WithLabelValues(metrics.LabelAnalyze).Inc()
			resultCh <- statistics.AnalyzeResult{
				Err: errAnalyzeWorkerPanic,
			}
		}
	}()
	for task := range taskCh {
		switch task.taskType {
		case colTask:
			resultCh <- analyzeColumnsPushdown(task.colExec)
		case idxTask:
			resultCh <- analyzeIndexPushdown(task.idxExec)
		}
	}
}

func analyzeIndexPushdown(idxExec *AnalyzeIndexExec) statistics.AnalyzeResult {
	hist, cms, err := idxExec.buildStats()
	if err != nil {
		return statistics.AnalyzeResult{Err: err}
	}
	result := statistics.AnalyzeResult{
		PhysicalTableID: idxExec.physicalTableID,
		Hist:            []*statistics.Histogram{hist},
		Cms:             []*statistics.CMSketch{cms},
		IsIndex:         1,
	}
	if hist.Len() > 0 {
		result.Count = hist.Buckets[hist.Len()-1].Count
	}
	return result
}

// AnalyzeIndexExec represents analyze index push down executor.
type AnalyzeIndexExec struct {
	ctx             sessionctx.Context
	physicalTableID int64
	idxInfo         *model.IndexInfo
	concurrency     int
	priority        int
	analyzePB       *tipb.AnalyzeReq
	result          distsql.SelectResult
	maxNumBuckets   uint64
}

func (e *AnalyzeIndexExec) open() error {
	var builder distsql.RequestBuilder
	kvReq, err := builder.SetIndexRanges(e.ctx.GetSessionVars().StmtCtx, e.physicalTableID, e.idxInfo.ID, ranger.FullRange()).
		SetAnalyzeRequest(e.analyzePB).
		SetKeepOrder(true).
		SetConcurrency(e.concurrency).
		Build()
	if err != nil {
		return errors.Trace(err)
	}
	ctx := context.TODO()
	e.result, err = distsql.Analyze(ctx, e.ctx.GetClient(), kvReq, e.ctx.GetSessionVars().KVVars, e.ctx.GetSessionVars().InRestrictedSQL)
	if err != nil {
		return errors.Trace(err)
	}
	e.result.Fetch(ctx)
	return nil
}

func (e *AnalyzeIndexExec) buildStats() (hist *statistics.Histogram, cms *statistics.CMSketch, err error) {
	if err = e.open(); err != nil {
		return nil, nil, errors.Trace(err)
	}
	defer func() {
		if err1 := e.result.Close(); err1 != nil {
			hist = nil
			cms = nil
			err = errors.Trace(err1)
		}
	}()
	hist = &statistics.Histogram{}
	cms = statistics.NewCMSketch(defaultCMSketchDepth, defaultCMSketchWidth)
	for {
		data, err := e.result.NextRaw(context.TODO())
		if err != nil {
			return nil, nil, errors.Trace(err)
		}
		if data == nil {
			break
		}
		resp := &tipb.AnalyzeIndexResp{}
		err = resp.Unmarshal(data)
		if err != nil {
			return nil, nil, errors.Trace(err)
		}
		hist, err = statistics.MergeHistograms(e.ctx.GetSessionVars().StmtCtx, hist, statistics.HistogramFromProto(resp.Hist), int(e.maxNumBuckets))
		if err != nil {
			return nil, nil, errors.Trace(err)
		}
		if resp.Cms != nil {
			err := cms.MergeCMSketch(statistics.CMSketchFromProto(resp.Cms))
			if err != nil {
				return nil, nil, errors.Trace(err)
			}
		}
	}
	hist.ID = e.idxInfo.ID
	return hist, cms, nil
}

func analyzeColumnsPushdown(colExec *AnalyzeColumnsExec) statistics.AnalyzeResult {
	hists, cms, err := colExec.buildStats()
	if err != nil {
		return statistics.AnalyzeResult{Err: err}
	}
	result := statistics.AnalyzeResult{
		PhysicalTableID: colExec.physicalTableID,
		Hist:            hists,
		Cms:             cms,
	}
	hist := hists[0]
	result.Count = hist.NullCount
	if hist.Len() > 0 {
		result.Count += hist.Buckets[hist.Len()-1].Count
	}
	return result
}

// AnalyzeColumnsExec represents Analyze columns push down executor.
type AnalyzeColumnsExec struct {
	ctx             sessionctx.Context
	physicalTableID int64
	colsInfo        []*model.ColumnInfo
	pkInfo          *model.ColumnInfo
	concurrency     int
	priority        int
	analyzePB       *tipb.AnalyzeReq
	resultHandler   *tableResultHandler
	maxNumBuckets   uint64
}

func (e *AnalyzeColumnsExec) open() error {
	var ranges []*ranger.Range
	if e.pkInfo != nil {
		ranges = ranger.FullIntRange(mysql.HasUnsignedFlag(e.pkInfo.Flag))
	} else {
		ranges = ranger.FullIntRange(false)
	}
	e.resultHandler = &tableResultHandler{}
	firstPartRanges, secondPartRanges := splitRanges(ranges, true)
	firstResult, err := e.buildResp(firstPartRanges)
	if err != nil {
		return errors.Trace(err)
	}
	if len(secondPartRanges) == 0 {
		e.resultHandler.open(nil, firstResult)
		return nil
	}
	var secondResult distsql.SelectResult
	secondResult, err = e.buildResp(secondPartRanges)
	if err != nil {
		return errors.Trace(err)
	}
	e.resultHandler.open(firstResult, secondResult)

	return nil
}

func (e *AnalyzeColumnsExec) buildResp(ranges []*ranger.Range) (distsql.SelectResult, error) {
	var builder distsql.RequestBuilder
	// Always set KeepOrder of the request to be true, in order to compute
	// correct `correlation` of columns.
	kvReq, err := builder.SetTableRanges(e.physicalTableID, ranges, nil).
		SetAnalyzeRequest(e.analyzePB).
		SetKeepOrder(true).
		SetConcurrency(e.concurrency).
		Build()
	if err != nil {
		return nil, errors.Trace(err)
	}
	ctx := context.TODO()
	result, err := distsql.Analyze(ctx, e.ctx.GetClient(), kvReq, e.ctx.GetSessionVars().KVVars, e.ctx.GetSessionVars().InRestrictedSQL)
	if err != nil {
		return nil, errors.Trace(err)
	}
	result.Fetch(ctx)
	return result, nil
}

func (e *AnalyzeColumnsExec) buildStats() (hists []*statistics.Histogram, cms []*statistics.CMSketch, err error) {
	if err = e.open(); err != nil {
		return nil, nil, errors.Trace(err)
	}
	defer func() {
		if err1 := e.resultHandler.Close(); err1 != nil {
			hists = nil
			cms = nil
			err = errors.Trace(err1)
		}
	}()
	pkHist := &statistics.Histogram{}
	collectors := make([]*statistics.SampleCollector, len(e.colsInfo))
	for i := range collectors {
		collectors[i] = &statistics.SampleCollector{
			IsMerger:      true,
			FMSketch:      statistics.NewFMSketch(maxSketchSize),
			MaxSampleSize: maxSampleSize,
			CMSketch:      statistics.NewCMSketch(defaultCMSketchDepth, defaultCMSketchWidth),
		}
	}
	for {
		data, err1 := e.resultHandler.nextRaw(context.TODO())
		if err1 != nil {
			return nil, nil, errors.Trace(err1)
		}
		if data == nil {
			break
		}
		resp := &tipb.AnalyzeColumnsResp{}
		err = resp.Unmarshal(data)
		if err != nil {
			return nil, nil, errors.Trace(err)
		}
		sc := e.ctx.GetSessionVars().StmtCtx
		if e.pkInfo != nil {
			pkHist, err = statistics.MergeHistograms(sc, pkHist, statistics.HistogramFromProto(resp.PkHist), int(e.maxNumBuckets))
			if err != nil {
				return nil, nil, errors.Trace(err)
			}
		}
		for i, rc := range resp.Collectors {
			collectors[i].MergeSampleCollector(sc, statistics.SampleCollectorFromProto(rc))
		}
	}
	timeZone := e.ctx.GetSessionVars().Location()
	if e.pkInfo != nil {
		pkHist.ID = e.pkInfo.ID
		err = pkHist.DecodeTo(&e.pkInfo.FieldType, timeZone)
		if err != nil {
			return nil, nil, errors.Trace(err)
		}
		hists = append(hists, pkHist)
		cms = append(cms, nil)
	}
	for i, col := range e.colsInfo {
		for j, s := range collectors[i].Samples {
			collectors[i].Samples[j].Ordinal = j
			collectors[i].Samples[j].Value, err = tablecodec.DecodeColumnValue(s.Value.GetBytes(), &col.FieldType, timeZone)
			if err != nil {
				return nil, nil, errors.Trace(err)
			}
		}
		hg, err := statistics.BuildColumn(e.ctx, int64(e.maxNumBuckets), col.ID, collectors[i], &col.FieldType)
		if err != nil {
			return nil, nil, errors.Trace(err)
		}
		hists = append(hists, hg)
		cms = append(cms, collectors[i].CMSketch)
	}
	return hists, cms, nil
}