// Copyright 2018 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"

	"github.com/pingcap/failpoint"
	"github.com/pingcap/parser/model"
	"github.com/pingcap/parser/mysql"
	"github.com/pingcap/tidb/expression"
	"github.com/pingcap/tidb/kv"
	plannercore "github.com/pingcap/tidb/planner/core"
	"github.com/pingcap/tidb/sessionctx"
	"github.com/pingcap/tidb/store/tikv"
	"github.com/pingcap/tidb/table"
	"github.com/pingcap/tidb/tablecodec"
	"github.com/pingcap/tidb/types"
	"github.com/pingcap/tidb/util/chunk"
	"github.com/pingcap/tidb/util/codec"
	"github.com/pingcap/tidb/util/execdetails"
	"github.com/pingcap/tidb/util/rowcodec"
)

func (b *executorBuilder) buildPointGet(p *plannercore.PointGetPlan) Executor {
	startTS, err := b.getSnapshotTS()
	if err != nil {
		b.err = err
		return nil
	}
	e := &PointGetExecutor{
		baseExecutor: newBaseExecutor(b.ctx, p.Schema(), p.ID()),
	}
	e.base().initCap = 1
	e.base().maxChunkSize = 1
	if p.Lock {
		b.hasLock = true
	}
	e.Init(p, startTS)
	return e
}

// PointGetExecutor executes point select query.
type PointGetExecutor struct {
	baseExecutor

	tblInfo      *model.TableInfo
	handle       int64
	idxInfo      *model.IndexInfo
	partInfo     *model.PartitionDefinition
	idxKey       kv.Key
	handleVal    []byte
	idxVals      []types.Datum
	startTS      uint64
	txn          kv.Transaction
	snapshot     kv.Snapshot
	done         bool
	lock         bool
	lockWaitTime int64
	rowDecoder   *rowcodec.ChunkDecoder

	columns []*model.ColumnInfo
	// virtualColumnIndex records all the indices of virtual columns and sort them in definition
	// to make sure we can compute the virtual column in right order.
	virtualColumnIndex []int

	// virtualColumnRetFieldTypes records the RetFieldTypes of virtual columns.
	virtualColumnRetFieldTypes []*types.FieldType

	stats *runtimeStatsWithSnapshot
}

// Init set fields needed for PointGetExecutor reuse, this does NOT change baseExecutor field
func (e *PointGetExecutor) Init(p *plannercore.PointGetPlan, startTs uint64) {
	decoder := NewRowDecoder(e.ctx, p.Schema(), p.TblInfo)
	e.tblInfo = p.TblInfo
	e.handle = p.Handle
	e.idxInfo = p.IndexInfo
	e.idxVals = p.IndexValues
	e.startTS = startTs
	e.done = false
	e.lock = p.Lock
	e.lockWaitTime = p.LockWaitTime
	e.rowDecoder = decoder
	e.partInfo = p.PartitionInfo
	e.columns = p.Columns
	e.buildVirtualColumnInfo()
}

// buildVirtualColumnInfo saves virtual column indices and sort them in definition order
func (e *PointGetExecutor) buildVirtualColumnInfo() {
	e.virtualColumnIndex = buildVirtualColumnIndex(e.Schema(), e.columns)
	if len(e.virtualColumnIndex) > 0 {
		e.virtualColumnRetFieldTypes = make([]*types.FieldType, len(e.virtualColumnIndex))
		for i, idx := range e.virtualColumnIndex {
			e.virtualColumnRetFieldTypes[i] = e.schema.Columns[idx].RetType
		}
	}
}

// Open implements the Executor interface.
func (e *PointGetExecutor) Open(context.Context) error {
	return nil
}

// Close implements the Executor interface.
func (e *PointGetExecutor) Close() error {
	if e.runtimeStats != nil && e.snapshot != nil {
		e.snapshot.DelOption(kv.CollectRuntimeStats)
	}
	e.done = false
	return nil
}

// Next implements the Executor interface.
func (e *PointGetExecutor) Next(ctx context.Context, req *chunk.Chunk) error {
	req.Reset()
	if e.done {
		return nil
	}
	e.done = true
	sessVars := e.ctx.GetSessionVars()
	txnCtx := sessVars.TxnCtx
	snapshotTS := e.startTS
	if e.lock {
		snapshotTS = txnCtx.GetForUpdateTS()
	}
	var err error
	e.txn, err = e.ctx.Txn(false)
	if err != nil {
		return err
	}
	if sessVars.InTxn() && txnCtx.StartTS == txnCtx.GetForUpdateTS() {
		e.snapshot = e.txn.GetSnapshot()
	} else {
		e.snapshot, err = e.ctx.GetStore().GetSnapshot(kv.Version{Ver: snapshotTS})
		if err != nil {
			return err
		}
	}
	if e.runtimeStats != nil {
		snapshotStats := &tikv.SnapshotRuntimeStats{}
		e.stats = &runtimeStatsWithSnapshot{
			SnapshotRuntimeStats: snapshotStats,
		}
		e.snapshot.SetOption(kv.CollectRuntimeStats, snapshotStats)
		e.ctx.GetSessionVars().StmtCtx.RuntimeStatsColl.RegisterStats(e.id, e.stats)
	}
	if e.ctx.GetSessionVars().GetReplicaRead().IsFollowerRead() {
		e.snapshot.SetOption(kv.ReplicaRead, kv.ReplicaReadFollower)
	}
	e.snapshot.SetOption(kv.TaskID, e.ctx.GetSessionVars().StmtCtx.TaskID)
	var tblID int64
	if e.partInfo != nil {
		tblID = e.partInfo.ID
	} else {
		tblID = e.tblInfo.ID
	}
	if e.idxInfo != nil {
		hasNull := false
		e.idxKey, hasNull, err = encodeIndexKey(e.base(), e.tblInfo, e.idxInfo, e.idxVals, tblID)
		if hasNull {
			return nil
		}
		if err != nil && !kv.ErrNotExist.Equal(err) {
			return err
		}

		e.handleVal, err = e.get(ctx, e.idxKey)
		if err != nil {
			if !kv.ErrNotExist.Equal(err) {
				return err
			}
		}
		if len(e.handleVal) == 0 {
			// handle is not found, try lock the index key if isolation level is not read consistency
			if e.ctx.GetSessionVars().IsPessimisticReadConsistency() {
				return nil
			}
			return e.lockKeyIfNeeded(ctx, e.idxKey)
		}
		e.handle, err = tablecodec.DecodeHandle(e.handleVal)
		if err != nil {
			return err
		}

		// The injection is used to simulate following scenario:
		// 1. Session A create a point get query but pause before second time `GET` kv from backend
		// 2. Session B create an UPDATE query to update the record that will be obtained in step 1
		// 3. Then point get retrieve data from backend after step 2 finished
		// 4. Check the result
		failpoint.InjectContext(ctx, "pointGetRepeatableReadTest-step1", func() {
			if ch, ok := ctx.Value("pointGetRepeatableReadTest").(chan struct{}); ok {
				// Make `UPDATE` continue
				close(ch)
			}
			// Wait `UPDATE` finished
			failpoint.InjectContext(ctx, "pointGetRepeatableReadTest-step2", nil)
		})
	}

	key := tablecodec.EncodeRowKeyWithHandle(tblID, e.handle)
	val, err := e.getAndLock(ctx, key)
	if err != nil {
		return err
	}
	if len(val) == 0 {
		if e.idxInfo != nil {
			return kv.ErrNotExist.GenWithStack("inconsistent extra index %s, handle %d not found in table",
				e.idxInfo.Name.O, e.handle)
		}
		return nil
	}
	err = DecodeRowValToChunk(e.base().ctx, e.schema, e.tblInfo, e.handle, val, req, e.rowDecoder)
	if err != nil {
		return err
	}

	err = FillVirtualColumnValue(e.virtualColumnRetFieldTypes, e.virtualColumnIndex,
		e.schema, e.columns, e.ctx, req)
	if err != nil {
		return err
	}
	return nil
}

func (e *PointGetExecutor) getAndLock(ctx context.Context, key kv.Key) (val []byte, err error) {
	if e.ctx.GetSessionVars().IsPessimisticReadConsistency() {
		// Only Lock the exist keys in RC isolation.
		val, err = e.get(ctx, key)
		if err != nil {
			if !kv.ErrNotExist.Equal(err) {
				return nil, err
			}
			return nil, nil
		}
		err = e.lockKeyIfNeeded(ctx, key)
		if err != nil {
			return nil, err
		}
		return val, nil
	}
	// Lock the key before get in RR isolation, then get will get the value from the cache.
	err = e.lockKeyIfNeeded(ctx, key)
	if err != nil {
		return nil, err
	}
	val, err = e.get(ctx, key)
	if err != nil {
		if !kv.ErrNotExist.Equal(err) {
			return nil, err
		}
		return nil, nil
	}
	return val, nil
}

func (e *PointGetExecutor) lockKeyIfNeeded(ctx context.Context, key []byte) error {
	if e.lock {
		seVars := e.ctx.GetSessionVars()
		lockCtx := newLockCtx(seVars, e.lockWaitTime)
		lockCtx.ReturnValues = true
		lockCtx.Values = map[string]kv.ReturnedValue{}
		err := doLockKeys(ctx, e.ctx, lockCtx, key)
		if err != nil {
			return err
		}
		lockCtx.ValuesLock.Lock()
		defer lockCtx.ValuesLock.Unlock()
		for key, val := range lockCtx.Values {
			if !val.AlreadyLocked {
				seVars.TxnCtx.SetPessimisticLockCache(kv.Key(key), val.Value)
			}
		}
		if len(e.handleVal) > 0 {
			seVars.TxnCtx.SetPessimisticLockCache(e.idxKey, e.handleVal)
		}
	}
	return nil
}

// get will first try to get from txn buffer, then check the pessimistic lock cache,
// then the store. Kv.ErrNotExist will be returned if key is not found
func (e *PointGetExecutor) get(ctx context.Context, key kv.Key) ([]byte, error) {
	if e.ctx.GetSessionVars().InTxn() && !e.txn.IsReadOnly() {
		// We cannot use txn.Get directly here because the snapshot in txn and the snapshot of e.snapshot may be
		// different for pessimistic transaction.
		val, err := e.txn.GetMemBuffer().Get(ctx, key)
		if err == nil {
			return val, err
		}
		if !kv.IsErrNotFound(err) {
			return nil, err
		}
		// key does not exist in mem buffer, check the lock cache
		if e.lock {
			var ok bool
			val, ok = e.ctx.GetSessionVars().TxnCtx.GetKeyInPessimisticLockCache(key)
			if ok {
				return val, nil
			}
		}
		// fallthrough to snapshot get.
	}
	return e.snapshot.Get(ctx, key)
}

func encodeIndexKey(e *baseExecutor, tblInfo *model.TableInfo, idxInfo *model.IndexInfo, idxVals []types.Datum, tID int64) (_ []byte, hasNull bool, err error) {
	sc := e.ctx.GetSessionVars().StmtCtx
	for i := range idxVals {
		if idxVals[i].IsNull() {
			hasNull = true
			continue
		}
		colInfo := tblInfo.Columns[idxInfo.Columns[i].Offset]
		// table.CastValue will append 0x0 if the string value's length is smaller than the BINARY column's length.
		// So we don't use CastValue for string value for now.
		// TODO: merge two if branch.
		if colInfo.Tp == mysql.TypeString || colInfo.Tp == mysql.TypeVarString || colInfo.Tp == mysql.TypeVarchar {
			var str string
			str, err = idxVals[i].ToString()
			idxVals[i].SetString(str, colInfo.FieldType.Collate)
		} else {
			idxVals[i], err = table.CastValue(e.ctx, idxVals[i], colInfo, true, false)
			if types.ErrOverflow.Equal(err) {
				return nil, false, kv.ErrNotExist
			}
		}
		if err != nil {
			return nil, false, err
		}
	}

	encodedIdxVals, err := codec.EncodeKey(sc, nil, idxVals...)
	if err != nil {
		return nil, false, err
	}
	return tablecodec.EncodeIndexSeekKey(tID, idxInfo.ID, encodedIdxVals), hasNull, nil
}

// DecodeRowValToChunk decodes row value into chunk checking row format used.
func DecodeRowValToChunk(sctx sessionctx.Context, schema *expression.Schema, tblInfo *model.TableInfo,
	handle int64, rowVal []byte, chk *chunk.Chunk, rd *rowcodec.ChunkDecoder) error {
	if rowcodec.IsNewFormat(rowVal) {
		return rd.DecodeToChunk(rowVal, handle, chk)
	}
	return decodeOldRowValToChunk(sctx, schema, tblInfo, handle, rowVal, chk)
}

func decodeOldRowValToChunk(sctx sessionctx.Context, schema *expression.Schema, tblInfo *model.TableInfo, handle int64,
	rowVal []byte, chk *chunk.Chunk) error {
	colID2CutPos := make(map[int64]int, schema.Len())
	for _, col := range schema.Columns {
		if _, ok := colID2CutPos[col.ID]; !ok {
			colID2CutPos[col.ID] = len(colID2CutPos)
		}
	}
	cutVals, err := tablecodec.CutRowNew(rowVal, colID2CutPos)
	if err != nil {
		return err
	}
	if cutVals == nil {
		cutVals = make([][]byte, len(colID2CutPos))
	}
	decoder := codec.NewDecoder(chk, sctx.GetSessionVars().Location())
	for i, col := range schema.Columns {
		// fill the virtual column value after row calculation
		if col.VirtualExpr != nil {
			chk.AppendNull(i)
			continue
		}
		if tblInfo.PKIsHandle && mysql.HasPriKeyFlag(col.RetType.Flag) {
			chk.AppendInt64(i, handle)
			continue
		}
		if col.ID == model.ExtraHandleID {
			chk.AppendInt64(i, handle)
			continue
		}
		cutPos := colID2CutPos[col.ID]
		if len(cutVals[cutPos]) == 0 {
			colInfo := getColInfoByID(tblInfo, col.ID)
			d, err1 := table.GetColOriginDefaultValue(sctx, colInfo)
			if err1 != nil {
				return err1
			}
			chk.AppendDatum(i, &d)
			continue
		}
		_, err = decoder.DecodeOne(cutVals[cutPos], i, col.RetType)
		if err != nil {
			return err
		}
	}
	return nil
}

func getColInfoByID(tbl *model.TableInfo, colID int64) *model.ColumnInfo {
	for _, col := range tbl.Columns {
		if col.ID == colID {
			return col
		}
	}
	return nil
}

type runtimeStatsWithSnapshot struct {
	*tikv.SnapshotRuntimeStats
}

func (e *runtimeStatsWithSnapshot) String() string {
	if e.SnapshotRuntimeStats != nil {
		return e.SnapshotRuntimeStats.String()
	}
	return ""
}

// Clone implements the RuntimeStats interface.
func (e *runtimeStatsWithSnapshot) Clone() execdetails.RuntimeStats {
	newRs := &runtimeStatsWithSnapshot{}
	if e.SnapshotRuntimeStats != nil {
		snapshotStats := e.SnapshotRuntimeStats.Clone()
		newRs.SnapshotRuntimeStats = snapshotStats.(*tikv.SnapshotRuntimeStats)
	}
	return newRs
}

// Merge implements the RuntimeStats interface.
func (e *runtimeStatsWithSnapshot) Merge(other execdetails.RuntimeStats) {
	tmp, ok := other.(*runtimeStatsWithSnapshot)
	if !ok {
		return
	}
	if tmp.SnapshotRuntimeStats != nil {
		if e.SnapshotRuntimeStats == nil {
			snapshotStats := tmp.SnapshotRuntimeStats.Clone()
			e.SnapshotRuntimeStats = snapshotStats.(*tikv.SnapshotRuntimeStats)
			return
		}
		e.SnapshotRuntimeStats.Merge(tmp.SnapshotRuntimeStats)
	}
}

// Tp implements the RuntimeStats interface.
func (e *runtimeStatsWithSnapshot) Tp() int {
	return execdetails.TpRuntimeStatsWithSnapshot
}
