/*
Copyright 2017 Google Inc. 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 spanner

import (
	"encoding/base64"
	"fmt"
	"math"
	"reflect"
	"strconv"
	"time"

	"cloud.google.com/go/civil"
	"cloud.google.com/go/internal/fields"
	proto "github.com/golang/protobuf/proto"
	proto3 "github.com/golang/protobuf/ptypes/struct"
	sppb "google.golang.org/genproto/googleapis/spanner/v1"
	"google.golang.org/grpc/codes"
)

// NullInt64 represents a Cloud Spanner INT64 that may be NULL.
type NullInt64 struct {
	Int64 int64
	Valid bool // Valid is true if Int64 is not NULL.
}

// String implements Stringer.String for NullInt64
func (n NullInt64) String() string {
	if !n.Valid {
		return fmt.Sprintf("%v", "<null>")
	}
	return fmt.Sprintf("%v", n.Int64)
}

// NullString represents a Cloud Spanner STRING that may be NULL.
type NullString struct {
	StringVal string
	Valid     bool // Valid is true if StringVal is not NULL.
}

// String implements Stringer.String for NullString
func (n NullString) String() string {
	if !n.Valid {
		return fmt.Sprintf("%v", "<null>")
	}
	return fmt.Sprintf("%q", n.StringVal)
}

// NullFloat64 represents a Cloud Spanner FLOAT64 that may be NULL.
type NullFloat64 struct {
	Float64 float64
	Valid   bool // Valid is true if Float64 is not NULL.
}

// String implements Stringer.String for NullFloat64
func (n NullFloat64) String() string {
	if !n.Valid {
		return fmt.Sprintf("%v", "<null>")
	}
	return fmt.Sprintf("%v", n.Float64)
}

// NullBool represents a Cloud Spanner BOOL that may be NULL.
type NullBool struct {
	Bool  bool
	Valid bool // Valid is true if Bool is not NULL.
}

// String implements Stringer.String for NullBool
func (n NullBool) String() string {
	if !n.Valid {
		return fmt.Sprintf("%v", "<null>")
	}
	return fmt.Sprintf("%v", n.Bool)
}

// NullTime represents a Cloud Spanner TIMESTAMP that may be null.
type NullTime struct {
	Time  time.Time
	Valid bool // Valid is true if Time is not NULL.
}

// String implements Stringer.String for NullTime
func (n NullTime) String() string {
	if !n.Valid {
		return fmt.Sprintf("%s", "<null>")
	}
	return fmt.Sprintf("%q", n.Time.Format(time.RFC3339Nano))
}

// NullDate represents a Cloud Spanner DATE that may be null.
type NullDate struct {
	Date  civil.Date
	Valid bool // Valid is true if Date is not NULL.
}

// String implements Stringer.String for NullDate
func (n NullDate) String() string {
	if !n.Valid {
		return fmt.Sprintf("%s", "<null>")
	}
	return fmt.Sprintf("%q", n.Date)
}

// NullRow represents a Cloud Spanner STRUCT that may be NULL.
// See also the document for Row.
// Note that NullRow is not a valid Cloud Spanner column Type.
type NullRow struct {
	Row   Row
	Valid bool // Valid is true if Row is not NULL.
}

// GenericColumnValue represents the generic encoded value and type of the
// column.  See google.spanner.v1.ResultSet proto for details.  This can be
// useful for proxying query results when the result types are not known in
// advance.
//
// If you populate a GenericColumnValue from a row using Row.Column or related
// methods, do not modify the contents of Type and Value.
type GenericColumnValue struct {
	Type  *sppb.Type
	Value *proto3.Value
}

// Decode decodes a GenericColumnValue. The ptr argument should be a pointer
// to a Go value that can accept v.
func (v GenericColumnValue) Decode(ptr interface{}) error {
	return decodeValue(v.Value, v.Type, ptr)
}

// NewGenericColumnValue creates a GenericColumnValue from Go value that is
// valid for Cloud Spanner.
func newGenericColumnValue(v interface{}) (*GenericColumnValue, error) {
	value, typ, err := encodeValue(v)
	if err != nil {
		return nil, err
	}
	return &GenericColumnValue{Value: value, Type: typ}, nil
}

// errTypeMismatch returns error for destination not having a compatible type
// with source Cloud Spanner type.
func errTypeMismatch(srcCode, elCode sppb.TypeCode, dst interface{}) error {
	s := srcCode.String()
	if srcCode == sppb.TypeCode_ARRAY {
		s = fmt.Sprintf("%v[%v]", srcCode, elCode)
	}
	return spannerErrorf(codes.InvalidArgument, "type %T cannot be used for decoding %s", dst, s)
}

// errNilSpannerType returns error for nil Cloud Spanner type in decoding.
func errNilSpannerType() error {
	return spannerErrorf(codes.FailedPrecondition, "unexpected nil Cloud Spanner data type in decoding")
}

// errNilSrc returns error for decoding from nil proto value.
func errNilSrc() error {
	return spannerErrorf(codes.FailedPrecondition, "unexpected nil Cloud Spanner value in decoding")
}

// errNilDst returns error for decoding into nil interface{}.
func errNilDst(dst interface{}) error {
	return spannerErrorf(codes.InvalidArgument, "cannot decode into nil type %T", dst)
}

// errNilArrElemType returns error for input Cloud Spanner data type being a array but without a
// non-nil array element type.
func errNilArrElemType(t *sppb.Type) error {
	return spannerErrorf(codes.FailedPrecondition, "array type %v is with nil array element type", t)
}

// errDstNotForNull returns error for decoding a SQL NULL value into a destination which doesn't
// support NULL values.
func errDstNotForNull(dst interface{}) error {
	return spannerErrorf(codes.InvalidArgument, "destination %T cannot support NULL SQL values", dst)
}

// errBadEncoding returns error for decoding wrongly encoded types.
func errBadEncoding(v *proto3.Value, err error) error {
	return spannerErrorf(codes.FailedPrecondition, "%v wasn't correctly encoded: <%v>", v, err)
}

func parseNullTime(v *proto3.Value, p *NullTime, code sppb.TypeCode, isNull bool) error {
	if p == nil {
		return errNilDst(p)
	}
	if code != sppb.TypeCode_TIMESTAMP {
		return errTypeMismatch(code, sppb.TypeCode_TYPE_CODE_UNSPECIFIED, p)
	}
	if isNull {
		*p = NullTime{}
		return nil
	}
	x, err := getStringValue(v)
	if err != nil {
		return err
	}
	y, err := time.Parse(time.RFC3339Nano, x)
	if err != nil {
		return errBadEncoding(v, err)
	}
	p.Valid = true
	p.Time = y
	return nil
}

// decodeValue decodes a protobuf Value into a pointer to a Go value, as
// specified by sppb.Type.
func decodeValue(v *proto3.Value, t *sppb.Type, ptr interface{}) error {
	if v == nil {
		return errNilSrc()
	}
	if t == nil {
		return errNilSpannerType()
	}
	code := t.Code
	acode := sppb.TypeCode_TYPE_CODE_UNSPECIFIED
	if code == sppb.TypeCode_ARRAY {
		if t.ArrayElementType == nil {
			return errNilArrElemType(t)
		}
		acode = t.ArrayElementType.Code
	}
	_, isNull := v.Kind.(*proto3.Value_NullValue)

	// Do the decoding based on the type of ptr.
	switch p := ptr.(type) {
	case nil:
		return errNilDst(nil)
	case *string:
		if p == nil {
			return errNilDst(p)
		}
		if code != sppb.TypeCode_STRING {
			return errTypeMismatch(code, acode, ptr)
		}
		if isNull {
			return errDstNotForNull(ptr)
		}
		x, err := getStringValue(v)
		if err != nil {
			return err
		}
		*p = x
	case *NullString:
		if p == nil {
			return errNilDst(p)
		}
		if code != sppb.TypeCode_STRING {
			return errTypeMismatch(code, acode, ptr)
		}
		if isNull {
			*p = NullString{}
			break
		}
		x, err := getStringValue(v)
		if err != nil {
			return err
		}
		p.Valid = true
		p.StringVal = x
	case *[]NullString:
		if p == nil {
			return errNilDst(p)
		}
		if acode != sppb.TypeCode_STRING {
			return errTypeMismatch(code, acode, ptr)
		}
		if isNull {
			*p = nil
			break
		}
		x, err := getListValue(v)
		if err != nil {
			return err
		}
		y, err := decodeStringArray(x)
		if err != nil {
			return err
		}
		*p = y
	case *[]byte:
		if p == nil {
			return errNilDst(p)
		}
		if code != sppb.TypeCode_BYTES {
			return errTypeMismatch(code, acode, ptr)
		}
		if isNull {
			*p = nil
			break
		}
		x, err := getStringValue(v)
		if err != nil {
			return err
		}
		y, err := base64.StdEncoding.DecodeString(x)
		if err != nil {
			return errBadEncoding(v, err)
		}
		*p = y
	case *[][]byte:
		if p == nil {
			return errNilDst(p)
		}
		if acode != sppb.TypeCode_BYTES {
			return errTypeMismatch(code, acode, ptr)
		}
		if isNull {
			*p = nil
			break
		}
		x, err := getListValue(v)
		if err != nil {
			return err
		}
		y, err := decodeByteArray(x)
		if err != nil {
			return err
		}
		*p = y
	case *int64:
		if p == nil {
			return errNilDst(p)
		}
		if code != sppb.TypeCode_INT64 {
			return errTypeMismatch(code, acode, ptr)
		}
		if isNull {
			return errDstNotForNull(ptr)
		}
		x, err := getStringValue(v)
		if err != nil {
			return err
		}
		y, err := strconv.ParseInt(x, 10, 64)
		if err != nil {
			return errBadEncoding(v, err)
		}
		*p = y
	case *NullInt64:
		if p == nil {
			return errNilDst(p)
		}
		if code != sppb.TypeCode_INT64 {
			return errTypeMismatch(code, acode, ptr)
		}
		if isNull {
			*p = NullInt64{}
			break
		}
		x, err := getStringValue(v)
		if err != nil {
			return err
		}
		y, err := strconv.ParseInt(x, 10, 64)
		if err != nil {
			return errBadEncoding(v, err)
		}
		p.Valid = true
		p.Int64 = y
	case *[]NullInt64:
		if p == nil {
			return errNilDst(p)
		}
		if acode != sppb.TypeCode_INT64 {
			return errTypeMismatch(code, acode, ptr)
		}
		if isNull {
			*p = nil
			break
		}
		x, err := getListValue(v)
		if err != nil {
			return err
		}
		y, err := decodeIntArray(x)
		if err != nil {
			return err
		}
		*p = y
	case *bool:
		if p == nil {
			return errNilDst(p)
		}
		if code != sppb.TypeCode_BOOL {
			return errTypeMismatch(code, acode, ptr)
		}
		if isNull {
			return errDstNotForNull(ptr)
		}
		x, err := getBoolValue(v)
		if err != nil {
			return err
		}
		*p = x
	case *NullBool:
		if p == nil {
			return errNilDst(p)
		}
		if code != sppb.TypeCode_BOOL {
			return errTypeMismatch(code, acode, ptr)
		}
		if isNull {
			*p = NullBool{}
			break
		}
		x, err := getBoolValue(v)
		if err != nil {
			return err
		}
		p.Valid = true
		p.Bool = x
	case *[]NullBool:
		if p == nil {
			return errNilDst(p)
		}
		if acode != sppb.TypeCode_BOOL {
			return errTypeMismatch(code, acode, ptr)
		}
		if isNull {
			*p = nil
			break
		}
		x, err := getListValue(v)
		if err != nil {
			return err
		}
		y, err := decodeBoolArray(x)
		if err != nil {
			return err
		}
		*p = y
	case *float64:
		if p == nil {
			return errNilDst(p)
		}
		if code != sppb.TypeCode_FLOAT64 {
			return errTypeMismatch(code, acode, ptr)
		}
		if isNull {
			return errDstNotForNull(ptr)
		}
		x, err := getFloat64Value(v)
		if err != nil {
			return err
		}
		*p = x
	case *NullFloat64:
		if p == nil {
			return errNilDst(p)
		}
		if code != sppb.TypeCode_FLOAT64 {
			return errTypeMismatch(code, acode, ptr)
		}
		if isNull {
			*p = NullFloat64{}
			break
		}
		x, err := getFloat64Value(v)
		if err != nil {
			return err
		}
		p.Valid = true
		p.Float64 = x
	case *[]NullFloat64:
		if p == nil {
			return errNilDst(p)
		}
		if acode != sppb.TypeCode_FLOAT64 {
			return errTypeMismatch(code, acode, ptr)
		}
		if isNull {
			*p = nil
			break
		}
		x, err := getListValue(v)
		if err != nil {
			return err
		}
		y, err := decodeFloat64Array(x)
		if err != nil {
			return err
		}
		*p = y
	case *time.Time:
		var nt NullTime
		if isNull {
			return errDstNotForNull(ptr)
		}
		err := parseNullTime(v, &nt, code, isNull)
		if err != nil {
			return nil
		}
		*p = nt.Time
	case *NullTime:
		err := parseNullTime(v, p, code, isNull)
		if err != nil {
			return err
		}
	case *[]NullTime:
		if p == nil {
			return errNilDst(p)
		}
		if acode != sppb.TypeCode_TIMESTAMP {
			return errTypeMismatch(code, acode, ptr)
		}
		if isNull {
			*p = nil
			break
		}
		x, err := getListValue(v)
		if err != nil {
			return err
		}
		y, err := decodeTimeArray(x)
		if err != nil {
			return err
		}
		*p = y
	case *civil.Date:
		if p == nil {
			return errNilDst(p)
		}
		if code != sppb.TypeCode_DATE {
			return errTypeMismatch(code, acode, ptr)
		}
		if isNull {
			return errDstNotForNull(ptr)
		}
		x, err := getStringValue(v)
		if err != nil {
			return err
		}
		y, err := civil.ParseDate(x)
		if err != nil {
			return errBadEncoding(v, err)
		}
		*p = y
	case *NullDate:
		if p == nil {
			return errNilDst(p)
		}
		if code != sppb.TypeCode_DATE {
			return errTypeMismatch(code, acode, ptr)
		}
		if isNull {
			*p = NullDate{}
			break
		}
		x, err := getStringValue(v)
		if err != nil {
			return err
		}
		y, err := civil.ParseDate(x)
		if err != nil {
			return errBadEncoding(v, err)
		}
		p.Valid = true
		p.Date = y
	case *[]NullDate:
		if p == nil {
			return errNilDst(p)
		}
		if acode != sppb.TypeCode_DATE {
			return errTypeMismatch(code, acode, ptr)
		}
		if isNull {
			*p = nil
			break
		}
		x, err := getListValue(v)
		if err != nil {
			return err
		}
		y, err := decodeDateArray(x)
		if err != nil {
			return err
		}
		*p = y
	case *[]NullRow:
		if p == nil {
			return errNilDst(p)
		}
		if acode != sppb.TypeCode_STRUCT {
			return errTypeMismatch(code, acode, ptr)
		}
		if isNull {
			*p = nil
			break
		}
		x, err := getListValue(v)
		if err != nil {
			return err
		}
		y, err := decodeRowArray(t.ArrayElementType.StructType, x)
		if err != nil {
			return err
		}
		*p = y
	case *GenericColumnValue:
		*p = GenericColumnValue{Type: t, Value: v}
	default:
		// Check if the proto encoding is for an array of structs.
		if !(code == sppb.TypeCode_ARRAY && acode == sppb.TypeCode_STRUCT) {
			return errTypeMismatch(code, acode, ptr)
		}
		vp := reflect.ValueOf(p)
		if !vp.IsValid() {
			return errNilDst(p)
		}
		if !isPtrStructPtrSlice(vp.Type()) {
			// The container is not a pointer to a struct pointer slice.
			return errTypeMismatch(code, acode, ptr)
		}
		// Only use reflection for nil detection on slow path.
		// Also, IsNil panics on many types, so check it after the type check.
		if vp.IsNil() {
			return errNilDst(p)
		}
		if isNull {
			// The proto Value is encoding NULL, set the pointer to struct
			// slice to nil as well.
			vp.Elem().Set(reflect.Zero(vp.Elem().Type()))
			break
		}
		x, err := getListValue(v)
		if err != nil {
			return err
		}
		if err = decodeStructArray(t.ArrayElementType.StructType, x, p); err != nil {
			return err
		}
	}
	return nil
}

// errSrvVal returns an error for getting a wrong source protobuf value in decoding.
func errSrcVal(v *proto3.Value, want string) error {
	return spannerErrorf(codes.FailedPrecondition, "cannot use %v(Kind: %T) as %s Value",
		v, v.GetKind(), want)
}

// getStringValue returns the string value encoded in proto3.Value v whose
// kind is proto3.Value_StringValue.
func getStringValue(v *proto3.Value) (string, error) {
	if x, ok := v.GetKind().(*proto3.Value_StringValue); ok && x != nil {
		return x.StringValue, nil
	}
	return "", errSrcVal(v, "String")
}

// getBoolValue returns the bool value encoded in proto3.Value v whose
// kind is proto3.Value_BoolValue.
func getBoolValue(v *proto3.Value) (bool, error) {
	if x, ok := v.GetKind().(*proto3.Value_BoolValue); ok && x != nil {
		return x.BoolValue, nil
	}
	return false, errSrcVal(v, "Bool")
}

// getListValue returns the proto3.ListValue contained in proto3.Value v whose
// kind is proto3.Value_ListValue.
func getListValue(v *proto3.Value) (*proto3.ListValue, error) {
	if x, ok := v.GetKind().(*proto3.Value_ListValue); ok && x != nil {
		return x.ListValue, nil
	}
	return nil, errSrcVal(v, "List")
}

// errUnexpectedNumStr returns error for decoder getting a unexpected string for
// representing special float values.
func errUnexpectedNumStr(s string) error {
	return spannerErrorf(codes.FailedPrecondition, "unexpected string value %q for number", s)
}

// getFloat64Value returns the float64 value encoded in proto3.Value v whose
// kind is proto3.Value_NumberValue / proto3.Value_StringValue.
// Cloud Spanner uses string to encode NaN, Infinity and -Infinity.
func getFloat64Value(v *proto3.Value) (float64, error) {
	switch x := v.GetKind().(type) {
	case *proto3.Value_NumberValue:
		if x == nil {
			break
		}
		return x.NumberValue, nil
	case *proto3.Value_StringValue:
		if x == nil {
			break
		}
		switch x.StringValue {
		case "NaN":
			return math.NaN(), nil
		case "Infinity":
			return math.Inf(1), nil
		case "-Infinity":
			return math.Inf(-1), nil
		default:
			return 0, errUnexpectedNumStr(x.StringValue)
		}
	}
	return 0, errSrcVal(v, "Number")
}

// errNilListValue returns error for unexpected nil ListValue in decoding Cloud Spanner ARRAYs.
func errNilListValue(sqlType string) error {
	return spannerErrorf(codes.FailedPrecondition, "unexpected nil ListValue in decoding %v array", sqlType)
}

// errDecodeArrayElement returns error for failure in decoding single array element.
func errDecodeArrayElement(i int, v proto.Message, sqlType string, err error) error {
	se, ok := toSpannerError(err).(*Error)
	if !ok {
		return spannerErrorf(codes.Unknown,
			"cannot decode %v(array element %v) as %v, error = <%v>", v, i, sqlType, err)
	}
	se.decorate(fmt.Sprintf("cannot decode %v(array element %v) as %v", v, i, sqlType))
	return se
}

// decodeStringArray decodes proto3.ListValue pb into a NullString slice.
func decodeStringArray(pb *proto3.ListValue) ([]NullString, error) {
	if pb == nil {
		return nil, errNilListValue("STRING")
	}
	a := make([]NullString, len(pb.Values))
	for i, v := range pb.Values {
		if err := decodeValue(v, stringType(), &a[i]); err != nil {
			return nil, errDecodeArrayElement(i, v, "STRING", err)
		}
	}
	return a, nil
}

// decodeIntArray decodes proto3.ListValue pb into a NullInt64 slice.
func decodeIntArray(pb *proto3.ListValue) ([]NullInt64, error) {
	if pb == nil {
		return nil, errNilListValue("INT64")
	}
	a := make([]NullInt64, len(pb.Values))
	for i, v := range pb.Values {
		if err := decodeValue(v, intType(), &a[i]); err != nil {
			return nil, errDecodeArrayElement(i, v, "INT64", err)
		}
	}
	return a, nil
}

// decodeBoolArray decodes proto3.ListValue pb into a NullBool slice.
func decodeBoolArray(pb *proto3.ListValue) ([]NullBool, error) {
	if pb == nil {
		return nil, errNilListValue("BOOL")
	}
	a := make([]NullBool, len(pb.Values))
	for i, v := range pb.Values {
		if err := decodeValue(v, boolType(), &a[i]); err != nil {
			return nil, errDecodeArrayElement(i, v, "BOOL", err)
		}
	}
	return a, nil
}

// decodeFloat64Array decodes proto3.ListValue pb into a NullFloat64 slice.
func decodeFloat64Array(pb *proto3.ListValue) ([]NullFloat64, error) {
	if pb == nil {
		return nil, errNilListValue("FLOAT64")
	}
	a := make([]NullFloat64, len(pb.Values))
	for i, v := range pb.Values {
		if err := decodeValue(v, floatType(), &a[i]); err != nil {
			return nil, errDecodeArrayElement(i, v, "FLOAT64", err)
		}
	}
	return a, nil
}

// decodeByteArray decodes proto3.ListValue pb into a slice of byte slice.
func decodeByteArray(pb *proto3.ListValue) ([][]byte, error) {
	if pb == nil {
		return nil, errNilListValue("BYTES")
	}
	a := make([][]byte, len(pb.Values))
	for i, v := range pb.Values {
		if err := decodeValue(v, bytesType(), &a[i]); err != nil {
			return nil, errDecodeArrayElement(i, v, "BYTES", err)
		}
	}
	return a, nil
}

// decodeTimeArray decodes proto3.ListValue pb into a NullTime slice.
func decodeTimeArray(pb *proto3.ListValue) ([]NullTime, error) {
	if pb == nil {
		return nil, errNilListValue("TIMESTAMP")
	}
	a := make([]NullTime, len(pb.Values))
	for i, v := range pb.Values {
		if err := decodeValue(v, timeType(), &a[i]); err != nil {
			return nil, errDecodeArrayElement(i, v, "TIMESTAMP", err)
		}
	}
	return a, nil
}

// decodeDateArray decodes proto3.ListValue pb into a NullDate slice.
func decodeDateArray(pb *proto3.ListValue) ([]NullDate, error) {
	if pb == nil {
		return nil, errNilListValue("DATE")
	}
	a := make([]NullDate, len(pb.Values))
	for i, v := range pb.Values {
		if err := decodeValue(v, dateType(), &a[i]); err != nil {
			return nil, errDecodeArrayElement(i, v, "DATE", err)
		}
	}
	return a, nil
}

func errNotStructElement(i int, v *proto3.Value) error {
	return errDecodeArrayElement(i, v, "STRUCT",
		spannerErrorf(codes.FailedPrecondition, "%v(type: %T) doesn't encode Cloud Spanner STRUCT", v, v))
}

// decodeRowArray decodes proto3.ListValue pb into a NullRow slice according to
// the structual information given in sppb.StructType ty.
func decodeRowArray(ty *sppb.StructType, pb *proto3.ListValue) ([]NullRow, error) {
	if pb == nil {
		return nil, errNilListValue("STRUCT")
	}
	a := make([]NullRow, len(pb.Values))
	for i := range pb.Values {
		switch v := pb.Values[i].GetKind().(type) {
		case *proto3.Value_ListValue:
			a[i] = NullRow{
				Row: Row{
					fields: ty.Fields,
					vals:   v.ListValue.Values,
				},
				Valid: true,
			}
		// Null elements not currently supported by the server, see
		// https://cloud.google.com/spanner/docs/query-syntax#using-structs-with-select
		case *proto3.Value_NullValue:
			// no-op, a[i] is NullRow{} already
		default:
			return nil, errNotStructElement(i, pb.Values[i])
		}
	}
	return a, nil
}

// errNilSpannerStructType returns error for unexpected nil Cloud Spanner STRUCT schema type in decoding.
func errNilSpannerStructType() error {
	return spannerErrorf(codes.FailedPrecondition, "unexpected nil StructType in decoding Cloud Spanner STRUCT")
}

// errUnnamedField returns error for decoding a Cloud Spanner STRUCT with unnamed field into a Go struct.
func errUnnamedField(ty *sppb.StructType, i int) error {
	return spannerErrorf(codes.InvalidArgument, "unnamed field %v in Cloud Spanner STRUCT %+v", i, ty)
}

// errNoOrDupGoField returns error for decoding a Cloud Spanner
// STRUCT into a Go struct which is either missing a field, or has duplicate fields.
func errNoOrDupGoField(s interface{}, f string) error {
	return spannerErrorf(codes.InvalidArgument, "Go struct %+v(type %T) has no or duplicate fields for Cloud Spanner STRUCT field %v", s, s, f)
}

// errDupColNames returns error for duplicated Cloud Spanner STRUCT field names found in decoding a Cloud Spanner STRUCT into a Go struct.
func errDupSpannerField(f string, ty *sppb.StructType) error {
	return spannerErrorf(codes.InvalidArgument, "duplicated field name %q in Cloud Spanner STRUCT %+v", f, ty)
}

// errDecodeStructField returns error for failure in decoding a single field of a Cloud Spanner STRUCT.
func errDecodeStructField(ty *sppb.StructType, f string, err error) error {
	se, ok := toSpannerError(err).(*Error)
	if !ok {
		return spannerErrorf(codes.Unknown,
			"cannot decode field %v of Cloud Spanner STRUCT %+v, error = <%v>", f, ty, err)
	}
	se.decorate(fmt.Sprintf("cannot decode field %v of Cloud Spanner STRUCT %+v", f, ty))
	return se
}

// decodeStruct decodes proto3.ListValue pb into struct referenced by pointer ptr, according to
// the structual information given in sppb.StructType ty.
func decodeStruct(ty *sppb.StructType, pb *proto3.ListValue, ptr interface{}) error {
	if reflect.ValueOf(ptr).IsNil() {
		return errNilDst(ptr)
	}
	if ty == nil {
		return errNilSpannerStructType()
	}
	// t holds the structual information of ptr.
	t := reflect.TypeOf(ptr).Elem()
	// v is the actual value that ptr points to.
	v := reflect.ValueOf(ptr).Elem()

	fields, err := fieldCache.Fields(t)
	if err != nil {
		return toSpannerError(err)
	}
	seen := map[string]bool{}
	for i, f := range ty.Fields {
		if f.Name == "" {
			return errUnnamedField(ty, i)
		}
		sf := fields.Match(f.Name)
		if sf == nil {
			return errNoOrDupGoField(ptr, f.Name)
		}
		if seen[f.Name] {
			// We don't allow duplicated field name.
			return errDupSpannerField(f.Name, ty)
		}
		// Try to decode a single field.
		if err := decodeValue(pb.Values[i], f.Type, v.FieldByIndex(sf.Index).Addr().Interface()); err != nil {
			return errDecodeStructField(ty, f.Name, err)
		}
		// Mark field f.Name as processed.
		seen[f.Name] = true
	}
	return nil
}

// isPtrStructPtrSlice returns true if ptr is a pointer to a slice of struct pointers.
func isPtrStructPtrSlice(t reflect.Type) bool {
	if t.Kind() != reflect.Ptr || t.Elem().Kind() != reflect.Slice {
		// t is not a pointer to a slice.
		return false
	}
	if t = t.Elem(); t.Elem().Kind() != reflect.Ptr || t.Elem().Elem().Kind() != reflect.Struct {
		// the slice that t points to is not a slice of struct pointers.
		return false
	}
	return true
}

// decodeStructArray decodes proto3.ListValue pb into struct slice referenced by pointer ptr, according to the
// structual information given in a sppb.StructType.
func decodeStructArray(ty *sppb.StructType, pb *proto3.ListValue, ptr interface{}) error {
	if pb == nil {
		return errNilListValue("STRUCT")
	}
	// Type of the struct pointers stored in the slice that ptr points to.
	ts := reflect.TypeOf(ptr).Elem().Elem()
	// The slice that ptr points to, might be nil at this point.
	v := reflect.ValueOf(ptr).Elem()
	// Allocate empty slice.
	v.Set(reflect.MakeSlice(v.Type(), 0, len(pb.Values)))
	// Decode every struct in pb.Values.
	for i, pv := range pb.Values {
		// Check if pv is a NULL value.
		if _, isNull := pv.Kind.(*proto3.Value_NullValue); isNull {
			// Append a nil pointer to the slice.
			v.Set(reflect.Append(v, reflect.New(ts).Elem()))
			continue
		}
		// Allocate empty struct.
		s := reflect.New(ts.Elem())
		// Get proto3.ListValue l from proto3.Value pv.
		l, err := getListValue(pv)
		if err != nil {
			return errDecodeArrayElement(i, pv, "STRUCT", err)
		}
		// Decode proto3.ListValue l into struct referenced by s.Interface().
		if err = decodeStruct(ty, l, s.Interface()); err != nil {
			return errDecodeArrayElement(i, pv, "STRUCT", err)
		}
		// Append the decoded struct back into the slice.
		v.Set(reflect.Append(v, s))
	}
	return nil
}

// errEncoderUnsupportedType returns error for not being able to encode a value of
// certain type.
func errEncoderUnsupportedType(v interface{}) error {
	return spannerErrorf(codes.InvalidArgument, "client doesn't support type %T", v)
}

// encodeValue encodes a Go native type into a proto3.Value.
func encodeValue(v interface{}) (*proto3.Value, *sppb.Type, error) {
	pb := &proto3.Value{
		Kind: &proto3.Value_NullValue{NullValue: proto3.NullValue_NULL_VALUE},
	}
	var pt *sppb.Type
	var err error
	switch v := v.(type) {
	case nil:
	case string:
		pb.Kind = stringKind(v)
		pt = stringType()
	case NullString:
		if v.Valid {
			return encodeValue(v.StringVal)
		}
		pt = stringType()
	case []string:
		if v != nil {
			pb, err = encodeArray(len(v), func(i int) interface{} { return v[i] })
			if err != nil {
				return nil, nil, err
			}
		}
		pt = listType(stringType())
	case []NullString:
		if v != nil {
			pb, err = encodeArray(len(v), func(i int) interface{} { return v[i] })
			if err != nil {
				return nil, nil, err
			}
		}
		pt = listType(stringType())
	case []byte:
		if v != nil {
			pb.Kind = stringKind(base64.StdEncoding.EncodeToString(v))
		}
		pt = bytesType()
	case [][]byte:
		if v != nil {
			pb, err = encodeArray(len(v), func(i int) interface{} { return v[i] })
			if err != nil {
				return nil, nil, err
			}
		}
		pt = listType(bytesType())
	case int:
		pb.Kind = stringKind(strconv.FormatInt(int64(v), 10))
		pt = intType()
	case []int:
		if v != nil {
			pb, err = encodeArray(len(v), func(i int) interface{} { return v[i] })
			if err != nil {
				return nil, nil, err
			}
		}
		pt = listType(intType())
	case int64:
		pb.Kind = stringKind(strconv.FormatInt(v, 10))
		pt = intType()
	case []int64:
		if v != nil {
			pb, err = encodeArray(len(v), func(i int) interface{} { return v[i] })
			if err != nil {
				return nil, nil, err
			}
		}
		pt = listType(intType())
	case NullInt64:
		if v.Valid {
			return encodeValue(v.Int64)
		}
		pt = intType()
	case []NullInt64:
		if v != nil {
			pb, err = encodeArray(len(v), func(i int) interface{} { return v[i] })
			if err != nil {
				return nil, nil, err
			}
		}
		pt = listType(intType())
	case bool:
		pb.Kind = &proto3.Value_BoolValue{BoolValue: v}
		pt = boolType()
	case []bool:
		if v != nil {
			pb, err = encodeArray(len(v), func(i int) interface{} { return v[i] })
			if err != nil {
				return nil, nil, err
			}
		}
		pt = listType(boolType())
	case NullBool:
		if v.Valid {
			return encodeValue(v.Bool)
		}
		pt = boolType()
	case []NullBool:
		if v != nil {
			pb, err = encodeArray(len(v), func(i int) interface{} { return v[i] })
			if err != nil {
				return nil, nil, err
			}
		}
		pt = listType(boolType())
	case float64:
		pb.Kind = &proto3.Value_NumberValue{NumberValue: v}
		pt = floatType()
	case []float64:
		if v != nil {
			pb, err = encodeArray(len(v), func(i int) interface{} { return v[i] })
			if err != nil {
				return nil, nil, err
			}
		}
		pt = listType(floatType())
	case NullFloat64:
		if v.Valid {
			return encodeValue(v.Float64)
		}
		pt = floatType()
	case []NullFloat64:
		if v != nil {
			pb, err = encodeArray(len(v), func(i int) interface{} { return v[i] })
			if err != nil {
				return nil, nil, err
			}
		}
		pt = listType(floatType())
	case time.Time:
		pb.Kind = stringKind(v.UTC().Format(time.RFC3339Nano))
		pt = timeType()
	case []time.Time:
		if v != nil {
			pb, err = encodeArray(len(v), func(i int) interface{} { return v[i] })
			if err != nil {
				return nil, nil, err
			}
		}
		pt = listType(timeType())
	case NullTime:
		if v.Valid {
			return encodeValue(v.Time)
		}
		pt = timeType()
	case []NullTime:
		if v != nil {
			pb, err = encodeArray(len(v), func(i int) interface{} { return v[i] })
			if err != nil {
				return nil, nil, err
			}
		}
		pt = listType(timeType())
	case civil.Date:
		pb.Kind = stringKind(v.String())
		pt = dateType()
	case []civil.Date:
		if v != nil {
			pb, err = encodeArray(len(v), func(i int) interface{} { return v[i] })
			if err != nil {
				return nil, nil, err
			}
		}
		pt = listType(dateType())
	case NullDate:
		if v.Valid {
			return encodeValue(v.Date)
		}
		pt = dateType()
	case []NullDate:
		if v != nil {
			pb, err = encodeArray(len(v), func(i int) interface{} { return v[i] })
			if err != nil {
				return nil, nil, err
			}
		}
		pt = listType(dateType())
	case GenericColumnValue:
		// Deep clone to ensure subsequent changes to v before
		// transmission don't affect our encoded value.
		pb = proto.Clone(v.Value).(*proto3.Value)
		pt = proto.Clone(v.Type).(*sppb.Type)
	default:
		return nil, nil, errEncoderUnsupportedType(v)
	}
	return pb, pt, nil
}

// encodeValueArray encodes a Value array into a proto3.ListValue.
func encodeValueArray(vs []interface{}) (*proto3.ListValue, error) {
	lv := &proto3.ListValue{}
	lv.Values = make([]*proto3.Value, 0, len(vs))
	for _, v := range vs {
		pb, _, err := encodeValue(v)
		if err != nil {
			return nil, err
		}
		lv.Values = append(lv.Values, pb)
	}
	return lv, nil
}

// encodeArray assumes that all values of the array element type encode without error.
func encodeArray(len int, at func(int) interface{}) (*proto3.Value, error) {
	vs := make([]*proto3.Value, len)
	var err error
	for i := 0; i < len; i++ {
		vs[i], _, err = encodeValue(at(i))
		if err != nil {
			return nil, err
		}
	}
	return listProto(vs...), nil
}

func spannerTagParser(t reflect.StructTag) (name string, keep bool, other interface{}, err error) {
	if s := t.Get("spanner"); s != "" {
		if s == "-" {
			return "", false, nil, nil
		}
		return s, true, nil, nil
	}
	return "", true, nil, nil
}

var fieldCache = fields.NewCache(spannerTagParser, nil, nil)