// Copyright 2016 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 tablecodec

import (
	"bytes"
	"encoding/binary"
	"math"
	"time"
	"unicode/utf8"

	"github.com/pingcap/errors"
	"github.com/pingcap/parser/charset"
	"github.com/pingcap/parser/model"
	"github.com/pingcap/parser/mysql"
	"github.com/pingcap/parser/terror"
	"github.com/pingcap/tidb/errno"
	"github.com/pingcap/tidb/kv"
	"github.com/pingcap/tidb/sessionctx/stmtctx"
	"github.com/pingcap/tidb/structure"
	"github.com/pingcap/tidb/types"
	"github.com/pingcap/tidb/util/codec"
	"github.com/pingcap/tidb/util/collate"
	"github.com/pingcap/tidb/util/dbterror"
	"github.com/pingcap/tidb/util/rowcodec"
)

var (
	errInvalidKey       = dbterror.ClassXEval.NewStd(errno.ErrInvalidKey)
	errInvalidRecordKey = dbterror.ClassXEval.NewStd(errno.ErrInvalidRecordKey)
	errInvalidIndexKey  = dbterror.ClassXEval.NewStd(errno.ErrInvalidIndexKey)
)

var (
	tablePrefix     = []byte{'t'}
	recordPrefixSep = []byte("_r")
	indexPrefixSep  = []byte("_i")
	metaPrefix      = []byte{'m'}
)

const (
	idLen     = 8
	prefixLen = 1 + idLen /*tableID*/ + 2
	// RecordRowKeyLen is public for calculating avgerage row size.
	RecordRowKeyLen       = prefixLen + idLen /*handle*/
	tablePrefixLength     = 1
	recordPrefixSepLength = 2
	metaPrefixLength      = 1
	// MaxOldEncodeValueLen is the maximum len of the old encoding of index value.
	MaxOldEncodeValueLen = 9
)

// TableSplitKeyLen is the length of key 't{table_id}' which is used for table split.
const TableSplitKeyLen = 1 + idLen

// TablePrefix returns table's prefix 't'.
func TablePrefix() []byte {
	return tablePrefix
}

// EncodeRowKey encodes the table id and record handle into a kv.Key
func EncodeRowKey(tableID int64, encodedHandle []byte) kv.Key {
	buf := make([]byte, 0, RecordRowKeyLen)
	buf = appendTableRecordPrefix(buf, tableID)
	buf = append(buf, encodedHandle...)
	return buf
}

// EncodeRowKeyWithHandle encodes the table id, row handle into a kv.Key
func EncodeRowKeyWithHandle(tableID int64, handle int64) kv.Key {
	buf := make([]byte, 0, RecordRowKeyLen)
	buf = appendTableRecordPrefix(buf, tableID)
	buf = codec.EncodeInt(buf, handle)
	return buf
}

// CutRowKeyPrefix cuts the row key prefix.
func CutRowKeyPrefix(key kv.Key) []byte {
	return key[prefixLen:]
}

// EncodeRecordKey encodes the recordPrefix, row handle into a kv.Key.
func EncodeRecordKey(recordPrefix kv.Key, h int64) kv.Key {
	buf := make([]byte, 0, len(recordPrefix)+idLen)
	buf = append(buf, recordPrefix...)
	buf = codec.EncodeInt(buf, h)
	return buf
}

func hasTablePrefix(key kv.Key) bool {
	return key[0] == tablePrefix[0]
}

func hasRecordPrefixSep(key kv.Key) bool {
	return key[0] == recordPrefixSep[0] && key[1] == recordPrefixSep[1]
}

// DecodeRecordKey decodes the key and gets the tableID, handle.
func DecodeRecordKey(key kv.Key) (tableID int64, handle int64, err error) {
	if len(key) <= prefixLen {
		return 0, 0, errInvalidRecordKey.GenWithStack("invalid record key - %q", key)
	}

	k := key
	if !hasTablePrefix(key) {
		return 0, 0, errInvalidRecordKey.GenWithStack("invalid record key - %q", k)
	}

	key = key[tablePrefixLength:]
	key, tableID, err = codec.DecodeInt(key)
	if err != nil {
		return 0, 0, errors.Trace(err)
	}

	if !hasRecordPrefixSep(key) {
		return 0, 0, errInvalidRecordKey.GenWithStack("invalid record key - %q", k)
	}

	key = key[recordPrefixSepLength:]
	key, handle, err = codec.DecodeInt(key)
	if err != nil {
		return 0, 0, errors.Trace(err)
	}
	return
}

// DecodeIndexKey decodes the key and gets the tableID, indexID, indexValues.
func DecodeIndexKey(key kv.Key) (tableID int64, indexID int64, indexValues []string, err error) {
	k := key

	tableID, indexID, key, err = DecodeIndexKeyPrefix(key)
	if err != nil {
		return 0, 0, nil, errors.Trace(err)
	}

	for len(key) > 0 {
		// FIXME: Without the schema information, we can only decode the raw kind of
		// the column. For instance, MysqlTime is internally saved as uint64.
		remain, d, e := codec.DecodeOne(key)
		if e != nil {
			return 0, 0, nil, errInvalidIndexKey.GenWithStack("invalid index key - %q %v", k, e)
		}
		str, e1 := d.ToString()
		if e1 != nil {
			return 0, 0, nil, errInvalidIndexKey.GenWithStack("invalid index key - %q %v", k, e1)
		}
		indexValues = append(indexValues, str)
		key = remain
	}
	return
}

// DecodeMetaKey decodes the key and get the meta key and meta field.
func DecodeMetaKey(ek kv.Key) (key []byte, field []byte, err error) {
	var tp uint64
	if !bytes.HasPrefix(ek, metaPrefix) {
		return nil, nil, errors.New("invalid encoded hash data key prefix")
	}
	ek = ek[metaPrefixLength:]
	ek, key, err = codec.DecodeBytes(ek, nil)
	if err != nil {
		return nil, nil, errors.Trace(err)
	}
	ek, tp, err = codec.DecodeUint(ek)
	if err != nil {
		return nil, nil, errors.Trace(err)
	} else if structure.TypeFlag(tp) != structure.HashData {
		return nil, nil, errors.Errorf("invalid encoded hash data key flag %c", byte(tp))
	}
	_, field, err = codec.DecodeBytes(ek, nil)
	return key, field, errors.Trace(err)
}

// DecodeIndexKeyPrefix decodes the key and gets the tableID, indexID, indexValues.
func DecodeIndexKeyPrefix(key kv.Key) (tableID int64, indexID int64, indexValues []byte, err error) {
	k := key

	tableID, indexID, isRecord, err := DecodeKeyHead(key)
	if err != nil {
		return 0, 0, nil, errors.Trace(err)
	}
	if isRecord {
		return 0, 0, nil, errInvalidIndexKey.GenWithStack("invalid index key - %q", k)
	}
	indexValues = key[prefixLen+idLen:]

	return tableID, indexID, indexValues, nil
}

// DecodeKeyHead decodes the key's head and gets the tableID, indexID. isRecordKey is true when is a record key.
func DecodeKeyHead(key kv.Key) (tableID int64, indexID int64, isRecordKey bool, err error) {
	isRecordKey = false
	k := key
	if !key.HasPrefix(tablePrefix) {
		err = errInvalidKey.GenWithStack("invalid key - %q", k)
		return
	}

	key = key[len(tablePrefix):]
	key, tableID, err = codec.DecodeInt(key)
	if err != nil {
		err = errors.Trace(err)
		return
	}

	if key.HasPrefix(recordPrefixSep) {
		isRecordKey = true
		return
	}
	if !key.HasPrefix(indexPrefixSep) {
		err = errInvalidKey.GenWithStack("invalid key - %q", k)
		return
	}

	key = key[len(indexPrefixSep):]

	key, indexID, err = codec.DecodeInt(key)
	if err != nil {
		err = errors.Trace(err)
		return
	}
	return
}

// DecodeTableID decodes the table ID of the key, if the key is not table key, returns 0.
func DecodeTableID(key kv.Key) int64 {
	if !key.HasPrefix(tablePrefix) {
		return 0
	}
	key = key[len(tablePrefix):]
	_, tableID, err := codec.DecodeInt(key)
	// TODO: return error.
	terror.Log(errors.Trace(err))
	return tableID
}

// DecodeRowKey decodes the key and gets the handle.
func DecodeRowKey(key kv.Key) (int64, error) {
	if len(key) != RecordRowKeyLen || !hasTablePrefix(key) || !hasRecordPrefixSep(key[prefixLen-2:]) {
		return 0, errInvalidKey.GenWithStack("invalid key - %q", key)
	}
	u := binary.BigEndian.Uint64(key[prefixLen:])
	return codec.DecodeCmpUintToInt(u), nil
}

// EncodeValue encodes a go value to bytes.
func EncodeValue(sc *stmtctx.StatementContext, b []byte, raw types.Datum) ([]byte, error) {
	var v types.Datum
	err := flatten(sc, raw, &v)
	if err != nil {
		return nil, err
	}
	return codec.EncodeValue(sc, b, v)
}

// EncodeRow encode row data and column ids into a slice of byte.
// valBuf and values pass by caller, for reducing EncodeRow allocates temporary bufs. If you pass valBuf and values as nil,
// EncodeRow will allocate it.
func EncodeRow(sc *stmtctx.StatementContext, row []types.Datum, colIDs []int64, valBuf []byte, values []types.Datum, e *rowcodec.Encoder) ([]byte, error) {
	if len(row) != len(colIDs) {
		return nil, errors.Errorf("EncodeRow error: data and columnID count not match %d vs %d", len(row), len(colIDs))
	}
	if e.Enable {
		return e.Encode(sc, colIDs, row, valBuf)
	}
	return EncodeOldRow(sc, row, colIDs, valBuf, values)
}

// EncodeOldRow encode row data and column ids into a slice of byte.
// Row layout: colID1, value1, colID2, value2, .....
// valBuf and values pass by caller, for reducing EncodeOldRow allocates temporary bufs. If you pass valBuf and values as nil,
// EncodeOldRow will allocate it.
func EncodeOldRow(sc *stmtctx.StatementContext, row []types.Datum, colIDs []int64, valBuf []byte, values []types.Datum) ([]byte, error) {
	if len(row) != len(colIDs) {
		return nil, errors.Errorf("EncodeRow error: data and columnID count not match %d vs %d", len(row), len(colIDs))
	}
	valBuf = valBuf[:0]
	if values == nil {
		values = make([]types.Datum, len(row)*2)
	}
	for i, c := range row {
		id := colIDs[i]
		values[2*i].SetInt64(id)
		err := flatten(sc, c, &values[2*i+1])
		if err != nil {
			return valBuf, errors.Trace(err)
		}
	}
	if len(values) == 0 {
		// We could not set nil value into kv.
		return append(valBuf, codec.NilFlag), nil
	}
	return codec.EncodeValue(sc, valBuf, values...)
}

func flatten(sc *stmtctx.StatementContext, data types.Datum, ret *types.Datum) error {
	switch data.Kind() {
	case types.KindMysqlTime:
		// for mysql datetime, timestamp and date type
		t := data.GetMysqlTime()
		if t.Type() == mysql.TypeTimestamp && sc.TimeZone != time.UTC {
			err := t.ConvertTimeZone(sc.TimeZone, time.UTC)
			if err != nil {
				return errors.Trace(err)
			}
		}
		v, err := t.ToPackedUint()
		ret.SetUint64(v)
		return errors.Trace(err)
	case types.KindMysqlDuration:
		// for mysql time type
		ret.SetInt64(int64(data.GetMysqlDuration().Duration))
		return nil
	case types.KindMysqlEnum:
		ret.SetUint64(data.GetMysqlEnum().Value)
		return nil
	case types.KindMysqlSet:
		ret.SetUint64(data.GetMysqlSet().Value)
		return nil
	case types.KindBinaryLiteral, types.KindMysqlBit:
		// We don't need to handle errors here since the literal is ensured to be able to store in uint64 in convertToMysqlBit.
		val, err := data.GetBinaryLiteral().ToInt(sc)
		if err != nil {
			return errors.Trace(err)
		}
		ret.SetUint64(val)
		return nil
	default:
		*ret = data
		return nil
	}
}

// DecodeColumnValue decodes data to a Datum according to the column info.
func DecodeColumnValue(data []byte, ft *types.FieldType, loc *time.Location) (types.Datum, error) {
	_, d, err := codec.DecodeOne(data)
	if err != nil {
		return types.Datum{}, errors.Trace(err)
	}
	colDatum, err := unflatten(d, ft, loc)
	if err != nil {
		return types.Datum{}, errors.Trace(err)
	}
	return colDatum, nil
}

// DecodeRowWithMapNew decode a row to datum map.
func DecodeRowWithMapNew(b []byte, cols map[int64]*types.FieldType, loc *time.Location, row map[int64]types.Datum) (map[int64]types.Datum, error) {
	if row == nil {
		row = make(map[int64]types.Datum, len(cols))
	}
	if b == nil {
		return row, nil
	}
	if len(b) == 1 && b[0] == codec.NilFlag {
		return row, nil
	}

	reqCols := make([]rowcodec.ColInfo, len(cols))
	var idx int
	for id, tp := range cols {
		reqCols[idx] = rowcodec.ColInfo{
			ID:      id,
			Tp:      int32(tp.Tp),
			Flag:    int32(tp.Flag),
			Flen:    tp.Flen,
			Decimal: tp.Decimal,
			Elems:   tp.Elems,
			Collate: tp.Collate,
		}
		idx++
	}
	// for decodeToMap:
	// - no need handle
	// - no need get default value
	rd := rowcodec.NewDatumMapDecoder(reqCols, -1, loc)
	return rd.DecodeToDatumMap(b, -1, row)
}

// DecodeRowWithMap decodes a byte slice into datums with a existing row map.
// Row layout: colID1, value1, colID2, value2, .....
func DecodeRowWithMap(b []byte, cols map[int64]*types.FieldType, loc *time.Location, row map[int64]types.Datum) (map[int64]types.Datum, error) {
	if row == nil {
		row = make(map[int64]types.Datum, len(cols))
	}
	if b == nil {
		return row, nil
	}
	if len(b) == 1 && b[0] == codec.NilFlag {
		return row, nil
	}
	cnt := 0
	var (
		data []byte
		err  error
	)
	for len(b) > 0 {
		// Get col id.
		data, b, err = codec.CutOne(b)
		if err != nil {
			return nil, errors.Trace(err)
		}
		_, cid, err := codec.DecodeOne(data)
		if err != nil {
			return nil, errors.Trace(err)
		}
		// Get col value.
		data, b, err = codec.CutOne(b)
		if err != nil {
			return nil, errors.Trace(err)
		}
		id := cid.GetInt64()
		ft, ok := cols[id]
		if ok {
			_, v, err := codec.DecodeOne(data)
			if err != nil {
				return nil, errors.Trace(err)
			}
			v, err = unflatten(v, ft, loc)
			if err != nil {
				return nil, errors.Trace(err)
			}
			row[id] = v
			cnt++
			if cnt == len(cols) {
				// Get enough data.
				break
			}
		}
	}
	return row, nil
}

// DecodeRow decodes a byte slice into datums.
// Row layout: colID1, value1, colID2, value2, .....
func DecodeRow(b []byte, cols map[int64]*types.FieldType, loc *time.Location) (map[int64]types.Datum, error) {
	if !rowcodec.IsNewFormat(b) {
		return DecodeRowWithMap(b, cols, loc, nil)
	}
	return DecodeRowWithMapNew(b, cols, loc, nil)
}

// CutRowNew cuts encoded row into byte slices and return columns' byte slice.
// Row layout: colID1, value1, colID2, value2, .....
func CutRowNew(data []byte, colIDs map[int64]int) ([][]byte, error) {
	if data == nil {
		return nil, nil
	}
	if len(data) == 1 && data[0] == codec.NilFlag {
		return nil, nil
	}

	var (
		cnt int
		b   []byte
		err error
		cid int64
	)
	row := make([][]byte, len(colIDs))
	for len(data) > 0 && cnt < len(colIDs) {
		// Get col id.
		data, cid, err = codec.CutColumnID(data)
		if err != nil {
			return nil, errors.Trace(err)
		}

		// Get col value.
		b, data, err = codec.CutOne(data)
		if err != nil {
			return nil, errors.Trace(err)
		}

		offset, ok := colIDs[cid]
		if ok {
			row[offset] = b
			cnt++
		}
	}
	return row, nil
}

// UnflattenDatums converts raw datums to column datums.
func UnflattenDatums(datums []types.Datum, fts []*types.FieldType, loc *time.Location) ([]types.Datum, error) {
	for i, datum := range datums {
		ft := fts[i]
		uDatum, err := unflatten(datum, ft, loc)
		if err != nil {
			return datums, errors.Trace(err)
		}
		datums[i] = uDatum
	}
	return datums, nil
}

// unflatten converts a raw datum to a column datum.
func unflatten(datum types.Datum, ft *types.FieldType, loc *time.Location) (types.Datum, error) {
	if datum.IsNull() {
		return datum, nil
	}
	switch ft.Tp {
	case mysql.TypeFloat:
		datum.SetFloat32(float32(datum.GetFloat64()))
		return datum, nil
	case mysql.TypeVarchar, mysql.TypeString, mysql.TypeVarString, mysql.TypeTinyBlob,
		mysql.TypeMediumBlob, mysql.TypeBlob, mysql.TypeLongBlob:
		datum.SetString(datum.GetString(), ft.Collate)
	case mysql.TypeTiny, mysql.TypeShort, mysql.TypeYear, mysql.TypeInt24,
		mysql.TypeLong, mysql.TypeLonglong, mysql.TypeDouble:
		return datum, nil
	case mysql.TypeDate, mysql.TypeDatetime, mysql.TypeTimestamp:
		t := types.NewTime(types.ZeroCoreTime, ft.Tp, int8(ft.Decimal))
		var err error
		err = t.FromPackedUint(datum.GetUint64())
		if err != nil {
			return datum, errors.Trace(err)
		}
		if ft.Tp == mysql.TypeTimestamp && !t.IsZero() {
			err = t.ConvertTimeZone(time.UTC, loc)
			if err != nil {
				return datum, errors.Trace(err)
			}
		}
		datum.SetUint64(0)
		datum.SetMysqlTime(t)
		return datum, nil
	case mysql.TypeDuration: //duration should read fsp from column meta data
		dur := types.Duration{Duration: time.Duration(datum.GetInt64()), Fsp: int8(ft.Decimal)}
		datum.SetMysqlDuration(dur)
		return datum, nil
	case mysql.TypeEnum:
		// ignore error deliberately, to read empty enum value.
		enum, err := types.ParseEnumValue(ft.Elems, datum.GetUint64())
		if err != nil {
			enum = types.Enum{}
		}
		datum.SetMysqlEnum(enum, ft.Collate)
		return datum, nil
	case mysql.TypeSet:
		set, err := types.ParseSetValue(ft.Elems, datum.GetUint64())
		if err != nil {
			return datum, errors.Trace(err)
		}
		datum.SetMysqlSet(set, ft.Collate)
		return datum, nil
	case mysql.TypeBit:
		val := datum.GetUint64()
		byteSize := (ft.Flen + 7) >> 3
		datum.SetUint64(0)
		datum.SetMysqlBit(types.NewBinaryLiteralFromUint(val, byteSize))
	}
	return datum, nil
}

// EncodeIndexSeekKey encodes an index value to kv.Key.
func EncodeIndexSeekKey(tableID int64, idxID int64, encodedValue []byte) kv.Key {
	key := make([]byte, 0, prefixLen+len(encodedValue))
	key = appendTableIndexPrefix(key, tableID)
	key = codec.EncodeInt(key, idxID)
	key = append(key, encodedValue...)
	return key
}

// CutIndexKey cuts encoded index key into colIDs to bytes slices map.
// The returned value b is the remaining bytes of the key which would be empty if it is unique index or handle data
// if it is non-unique index.
func CutIndexKey(key kv.Key, colIDs []int64) (values map[int64][]byte, b []byte, err error) {
	b = key[prefixLen+idLen:]
	values = make(map[int64][]byte, len(colIDs))
	for _, id := range colIDs {
		var val []byte
		val, b, err = codec.CutOne(b)
		if err != nil {
			return nil, nil, errors.Trace(err)
		}
		values[id] = val
	}
	return
}

// CutIndexPrefix cuts the index prefix.
func CutIndexPrefix(key kv.Key) []byte {
	return key[prefixLen+idLen:]
}

// CutIndexKeyNew cuts encoded index key into colIDs to bytes slices.
// The returned value b is the remaining bytes of the key which would be empty if it is unique index or handle data
// if it is non-unique index.
func CutIndexKeyNew(key kv.Key, length int) (values [][]byte, b []byte, err error) {
	b = key[prefixLen+idLen:]
	values = make([][]byte, 0, length)
	for i := 0; i < length; i++ {
		var val []byte
		val, b, err = codec.CutOne(b)
		if err != nil {
			return nil, nil, errors.Trace(err)
		}
		values = append(values, val)
	}
	return
}

// HandleStatus is the handle status in index.
type HandleStatus int

const (
	// HandleNotExists means no need to decode handle value when DecodeIndexKV.
	HandleNotExists HandleStatus = iota
	// HandleIsSigned means decode handle value as int64 when DecodeIndexKV.
	HandleIsSigned
	// HandleIsUnsigned means decode handle value as uint64 when DecodeIndexKV.
	HandleIsUnsigned
)

func handleExists(hdStatus HandleStatus) bool {
	return hdStatus != HandleNotExists
}

// reEncodeHandleByStatus first decode the value into a int or uint decided by the hdStatus, then encode it so that it can
// be properly decoded.
func reEncodeHandleByStatus(value []byte, hdStatus HandleStatus) ([]byte, error) {
	handle, err := DecodeIndexValueAsHandle(value)
	if err != nil {
		return nil, errors.Trace(err)
	}
	var handleDatum types.Datum
	if hdStatus == HandleIsUnsigned {
		handleDatum = types.NewUintDatum(uint64(handle))
	} else {
		handleDatum = types.NewIntDatum(handle)
	}
	handleBytes := make([]byte, 0, 8)
	handleBytes, err = codec.EncodeValue(nil, handleBytes, handleDatum)
	if err != nil {
		return nil, errors.Trace(err)
	}
	return handleBytes, nil
}

func decodeIndexKvNewCollation(key, value []byte, colsLen int, hdStatus HandleStatus, columns []rowcodec.ColInfo) ([][]byte, error) {
	colIDs := make(map[int64]int, len(columns))
	for i, col := range columns {
		colIDs[col.ID] = i
	}
	// We don't need to decode handle here, and colIDs >= 0 always.
	rd := rowcodec.NewByteDecoder(columns, -1, nil, nil)
	vLen := len(value)
	tailLen := int(value[0])
	resultValues, err := rd.DecodeToBytesNoHandle(colIDs, value[1:vLen-tailLen])
	if err != nil {
		return nil, errors.Trace(err)
	}

	if tailLen < 8 {
		// In non-unique index.
		if handleExists(hdStatus) {
			resultValues = append(resultValues, key[len(key)-9:])
		}
	} else {
		// In unique index.
		if handleExists(hdStatus) {
			handleBytes, err := reEncodeHandleByStatus(value[vLen-tailLen:], hdStatus)
			if err != nil {
				return nil, errors.Trace(err)
			}
			resultValues = append(resultValues, handleBytes)
		}
	}
	return resultValues, nil
}

func decodeIndexKvOldCollation(key, value []byte, colsLen int, hdStatus HandleStatus) ([][]byte, error) {
	resultValues, b, err := CutIndexKeyNew(key, colsLen)
	if err != nil {
		return nil, errors.Trace(err)
	}
	if len(b) > 0 {
		// non-unique index
		if handleExists(hdStatus) {
			resultValues = append(resultValues, b)
		}
	} else if handleExists(hdStatus) {
		// unique index
		handleBytes, err := reEncodeHandleByStatus(value, hdStatus)
		if err != nil {
			return nil, errors.Trace(err)
		}
		resultValues = append(resultValues, handleBytes)
	}
	return resultValues, nil
}

// DecodeIndexKV uses to decode index key values.
func DecodeIndexKV(key, value []byte, colsLen int, hdStatus HandleStatus, columns []rowcodec.ColInfo) ([][]byte, error) {
	if len(value) > MaxOldEncodeValueLen {
		return decodeIndexKvNewCollation(key, value, colsLen, hdStatus, columns)
	}
	return decodeIndexKvOldCollation(key, value, colsLen, hdStatus)
}

// DecodeIndexHandle uses to decode the handle from index key/value.
func DecodeIndexHandle(key, value []byte, colsLen int, pkTp *types.FieldType) (int64, error) {
	_, b, err := CutIndexKeyNew(key, colsLen)
	if err != nil {
		return 0, errors.Trace(err)
	}
	if len(b) > 0 {
		d, err := DecodeColumnValue(b, pkTp, nil)
		if err != nil {
			return 0, errors.Trace(err)
		}
		return d.GetInt64(), nil

	} else if len(value) >= 8 {
		return decodeHandleInIndexValue(value)
	}
	// Should never execute to here.
	return 0, errors.Errorf("no handle in index key: %v, value: %v", key, value)
}

func decodeHandleInIndexValue(value []byte) (int64, error) {
	if len(value) > MaxOldEncodeValueLen {
		tailLen := value[0]
		if tailLen >= 8 {
			return DecodeIndexValueAsHandle(value[len(value)-int(tailLen):])
		}
		// Should never executed to here, since the handle is encoded in IndexKey.
		return 0, errors.Errorf("no handle in index value: %v", value)
	}
	return DecodeIndexValueAsHandle(value)
}

// DecodeIndexValueAsHandle uses to decode index value as handle id.
func DecodeIndexValueAsHandle(data []byte) (int64, error) {
	var h int64
	buf := bytes.NewBuffer(data)
	err := binary.Read(buf, binary.BigEndian, &h)
	return h, errors.Trace(err)
}

// EncodeTableIndexPrefix encodes index prefix with tableID and idxID.
func EncodeTableIndexPrefix(tableID, idxID int64) kv.Key {
	key := make([]byte, 0, prefixLen)
	key = appendTableIndexPrefix(key, tableID)
	key = codec.EncodeInt(key, idxID)
	return key
}

// EncodeTablePrefix encodes table prefix with table ID.
func EncodeTablePrefix(tableID int64) kv.Key {
	var key kv.Key
	key = append(key, tablePrefix...)
	key = codec.EncodeInt(key, tableID)
	return key
}

// appendTableRecordPrefix appends table record prefix  "t[tableID]_r".
func appendTableRecordPrefix(buf []byte, tableID int64) []byte {
	buf = append(buf, tablePrefix...)
	buf = codec.EncodeInt(buf, tableID)
	buf = append(buf, recordPrefixSep...)
	return buf
}

// appendTableIndexPrefix appends table index prefix  "t[tableID]_i".
func appendTableIndexPrefix(buf []byte, tableID int64) []byte {
	buf = append(buf, tablePrefix...)
	buf = codec.EncodeInt(buf, tableID)
	buf = append(buf, indexPrefixSep...)
	return buf
}

// ReplaceRecordKeyTableID replace the tableID in the recordKey buf.
func ReplaceRecordKeyTableID(buf []byte, tableID int64) []byte {
	if len(buf) < len(tablePrefix)+8 {
		return buf
	}

	u := codec.EncodeIntToCmpUint(tableID)
	binary.BigEndian.PutUint64(buf[len(tablePrefix):], u)
	return buf
}

// GenTableRecordPrefix composes record prefix with tableID: "t[tableID]_r".
func GenTableRecordPrefix(tableID int64) kv.Key {
	buf := make([]byte, 0, len(tablePrefix)+8+len(recordPrefixSep))
	return appendTableRecordPrefix(buf, tableID)
}

// GenTableIndexPrefix composes index prefix with tableID: "t[tableID]_i".
func GenTableIndexPrefix(tableID int64) kv.Key {
	buf := make([]byte, 0, len(tablePrefix)+8+len(indexPrefixSep))
	return appendTableIndexPrefix(buf, tableID)
}

// IsIndexKey is used to check whether the key is an index key.
func IsIndexKey(k []byte) bool {
	return len(k) > 11 && k[0] == 't' && k[10] == 'i'
}

// IsUntouchedIndexKValue uses to check whether the key is index key, and the value is untouched,
// since the untouched index key/value is no need to commit.
func IsUntouchedIndexKValue(k, v []byte) bool {
	if !IsIndexKey(k) {
		return false
	}
	vLen := len(v)
	if vLen <= MaxOldEncodeValueLen {
		return (vLen == 1 || vLen == 9) && v[vLen-1] == kv.UnCommitIndexKVFlag
	}
	// New index value format
	tailLen := int(v[0])
	if tailLen < 8 {
		// Non-unique index.
		return tailLen >= 1 && v[vLen-1] == kv.UnCommitIndexKVFlag
	}
	// Unique index
	return tailLen == 9
}

// GenTablePrefix composes table record and index prefix: "t[tableID]".
func GenTablePrefix(tableID int64) kv.Key {
	buf := make([]byte, 0, len(tablePrefix)+8)
	buf = append(buf, tablePrefix...)
	buf = codec.EncodeInt(buf, tableID)
	return buf
}

// TruncateToRowKeyLen truncates the key to row key length if the key is longer than row key.
func TruncateToRowKeyLen(key kv.Key) kv.Key {
	if len(key) > RecordRowKeyLen {
		return key[:RecordRowKeyLen]
	}
	return key
}

// GetTableHandleKeyRange returns table handle's key range with tableID.
func GetTableHandleKeyRange(tableID int64) (startKey, endKey []byte) {
	startKey = EncodeRowKeyWithHandle(tableID, math.MinInt64)
	endKey = EncodeRowKeyWithHandle(tableID, math.MaxInt64)
	return
}

// GetTableIndexKeyRange returns table index's key range with tableID and indexID.
func GetTableIndexKeyRange(tableID, indexID int64) (startKey, endKey []byte) {
	startKey = EncodeIndexSeekKey(tableID, indexID, nil)
	endKey = EncodeIndexSeekKey(tableID, indexID, []byte{255})
	return
}

// GetIndexKeyBuf reuse or allocate buffer.
func GetIndexKeyBuf(buf []byte, defaultCap int) []byte {
	if buf != nil {
		return buf[:0]
	}

	return make([]byte, 0, defaultCap)
}

// GenIndexKey generates index key using input physical table id.
func GenIndexKey(sc *stmtctx.StatementContext, tblInfo *model.TableInfo, idxInfo *model.IndexInfo,
	phyTblID int64, indexedValues []types.Datum, h int64, buf []byte) (key []byte, distinct bool, err error) {
	if idxInfo.Unique {
		// See https://dev.mysql.com/doc/refman/5.7/en/create-index.html
		// A UNIQUE index creates a constraint such that all values in the index must be distinct.
		// An error occurs if you try to add a new row with a key value that matches an existing row.
		// For all engines, a UNIQUE index permits multiple NULL values for columns that can contain NULL.
		distinct = true
		for _, cv := range indexedValues {
			if cv.IsNull() {
				distinct = false
				break
			}
		}
	}

	// For string columns, indexes can be created using only the leading part of column values,
	// using col_name(length) syntax to specify an index prefix length.
	indexedValues = TruncateIndexValuesIfNeeded(tblInfo, idxInfo, indexedValues)
	key = GetIndexKeyBuf(buf, RecordRowKeyLen+len(indexedValues)*9+9)
	key = appendTableIndexPrefix(key, phyTblID)
	key = codec.EncodeInt(key, idxInfo.ID)
	key, err = codec.EncodeKey(sc, key, indexedValues...)
	if err != nil {
		return nil, false, err
	}
	if !distinct {
		key, err = codec.EncodeKey(sc, key, types.NewDatum(h))
		if err != nil {
			return nil, false, err
		}
	}
	return
}

// GenIndexValue creates encoded index value and returns the result.
func GenIndexValue(sc *stmtctx.StatementContext, tblInfo *model.TableInfo, idxInfo *model.IndexInfo,
	containNonBinaryString bool, distinct bool, untouched bool, indexedValues []types.Datum, h int64) ([]byte, error) {
	var idxVal []byte
	if collate.NewCollationEnabled() && containNonBinaryString {
		colIds := make([]int64, len(idxInfo.Columns))
		for i, col := range idxInfo.Columns {
			colIds[i] = tblInfo.Columns[col.Offset].ID
		}
		rd := rowcodec.Encoder{Enable: true}
		rowRestoredValue, err := rd.Encode(sc, colIds, indexedValues, nil)
		if err != nil {
			return nil, err
		}
		idxVal = make([]byte, 1+len(rowRestoredValue))
		copy(idxVal[1:], rowRestoredValue)
		tailLen := 0
		if distinct {
			// The len of the idxVal is always >= 10 since len (restoredValue) > 0.
			tailLen += 8
			idxVal = append(idxVal, EncodeHandle(h)...)
		} else if len(idxVal) < 10 {
			// Padding the len to 10
			paddingLen := 10 - len(idxVal)
			tailLen += paddingLen
			idxVal = append(idxVal, bytes.Repeat([]byte{0x0}, paddingLen)...)
		}
		if untouched {
			// If index is untouched and fetch here means the key is exists in TiKV, but not in txn mem-buffer,
			// then should also write the untouched index key/value to mem-buffer to make sure the data
			// is consistent with the index in txn mem-buffer.
			tailLen += 1
			idxVal = append(idxVal, kv.UnCommitIndexKVFlag)
		}
		idxVal[0] = byte(tailLen)
	} else {
		idxVal = make([]byte, 0)
		if distinct {
			idxVal = EncodeHandle(h)
		}
		if untouched {
			// If index is untouched and fetch here means the key is exists in TiKV, but not in txn mem-buffer,
			// then should also write the untouched index key/value to mem-buffer to make sure the data
			// is consistent with the index in txn mem-buffer.
			idxVal = append(idxVal, kv.UnCommitIndexKVFlag)
		}
		if len(idxVal) == 0 {
			idxVal = []byte{'0'}
		}
	}
	return idxVal, nil
}

// TruncateIndexValuesIfNeeded truncates the index values created using only the leading part of column values.
func TruncateIndexValuesIfNeeded(tblInfo *model.TableInfo, idxInfo *model.IndexInfo, indexedValues []types.Datum) []types.Datum {
	for i := 0; i < len(indexedValues); i++ {
		v := &indexedValues[i]
		if v.Kind() == types.KindString || v.Kind() == types.KindBytes {
			ic := idxInfo.Columns[i]
			colCharset := tblInfo.Columns[ic.Offset].Charset
			colValue := v.GetBytes()
			isUTF8Charset := colCharset == charset.CharsetUTF8 || colCharset == charset.CharsetUTF8MB4
			origKind := v.Kind()
			if isUTF8Charset {
				if ic.Length != types.UnspecifiedLength && utf8.RuneCount(colValue) > ic.Length {
					rs := bytes.Runes(colValue)
					truncateStr := string(rs[:ic.Length])
					// truncate value and limit its length
					v.SetString(truncateStr, tblInfo.Columns[ic.Offset].Collate)
					if origKind == types.KindBytes {
						v.SetBytes(v.GetBytes())
					}
				}
			} else if ic.Length != types.UnspecifiedLength && len(colValue) > ic.Length {
				// truncate value and limit its length
				v.SetBytes(colValue[:ic.Length])
				if origKind == types.KindString {
					v.SetString(v.GetString(), tblInfo.Columns[ic.Offset].Collate)
				}
			}
		}
	}

	return indexedValues
}

// EncodeHandle encodes handle in data.
func EncodeHandle(h int64) []byte {
	var data [8]byte
	binary.BigEndian.PutUint64(data[:], uint64(h))
	return data[:]
}

// DecodeHandle decodes handle in data.
func DecodeHandle(data []byte) (int64, error) {
	dLen := len(data)
	if dLen <= MaxOldEncodeValueLen {
		return int64(binary.BigEndian.Uint64(data)), nil
	}
	return int64(binary.BigEndian.Uint64(data[dLen-int(data[0]):])), nil
}