// Copyright 2020 Dolthub, 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,
// 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 typeinfo

import (
	"context"
	"encoding/binary"
	"fmt"
	"io"
	"strconv"
	"strings"
	"unsafe"

	"github.com/dolthub/go-mysql-server/sql"
	"github.com/dolthub/vitess/go/sqltypes"

	"github.com/dolthub/dolt/go/store/types"
)

const (
	varBinaryTypeParam_Length = "length"
)

// As a type, this is modeled more after MySQL's story for binary data. There, it's treated
// as a string that is interpreted as raw bytes, rather than as a bespoke data structure,
// and thus this is mirrored here in its implementation. This will minimize any differences
// that could arise.
//
// This type handles the BLOB types. BINARY and VARBINARY are handled by inlineBlobType.
type varBinaryType struct {
	sqlBinaryType sql.StringType
}

var _ TypeInfo = (*varBinaryType)(nil)

var (
	TinyBlobType   TypeInfo = &varBinaryType{sqlBinaryType: sql.TinyBlob}
	BlobType       TypeInfo = &varBinaryType{sqlBinaryType: sql.Blob}
	MediumBlobType TypeInfo = &varBinaryType{sqlBinaryType: sql.MediumBlob}
	LongBlobType   TypeInfo = &varBinaryType{sqlBinaryType: sql.LongBlob}
)

func CreateVarBinaryTypeFromParams(params map[string]string) (TypeInfo, error) {
	var length int64
	var err error
	if lengthStr, ok := params[varBinaryTypeParam_Length]; ok {
		length, err = strconv.ParseInt(lengthStr, 10, 64)
		if err != nil {
			return nil, err
		}
	} else {
		return nil, fmt.Errorf(`create varbinary type info is missing param "%v"`, varBinaryTypeParam_Length)
	}
	sqlType, err := sql.CreateBinary(sqltypes.Blob, length)
	if err != nil {
		return nil, err
	}
	return &varBinaryType{sqlType}, nil
}

// ConvertNomsValueToValue implements TypeInfo interface.
func (ti *varBinaryType) ConvertNomsValueToValue(v types.Value) (interface{}, error) {
	if val, ok := v.(types.Blob); ok {
		return fromBlob(val)
	}
	if _, ok := v.(types.Null); ok || v == nil {
		return nil, nil
	}
	return nil, fmt.Errorf(`"%v" cannot convert NomsKind "%v" to a value`, ti.String(), v.Kind())
}

// ReadFrom reads a go value from a noms types.CodecReader directly
func (ti *varBinaryType) ReadFrom(_ *types.NomsBinFormat, reader types.CodecReader) (interface{}, error) {
	k := reader.PeekKind()
	switch k {
	case types.BlobKind:
		val, err := reader.ReadBlob()
		if err != nil {
			return nil, err
		}
		return fromBlob(val)
	case types.NullKind:
		_ = reader.ReadKind()
		return nil, nil
	}

	return nil, fmt.Errorf(`"%v" cannot convert NomsKind "%v" to a value`, ti.String(), k)
}

// ConvertValueToNomsValue implements TypeInfo interface.
func (ti *varBinaryType) ConvertValueToNomsValue(ctx context.Context, vrw types.ValueReadWriter, v interface{}) (types.Value, error) {
	if v == nil {
		return types.NullValue, nil
	}
	strVal, err := ti.sqlBinaryType.Convert(v)
	if err != nil {
		return nil, err
	}
	val, ok := strVal.([]byte)
	if ok {
		return types.NewBlob(ctx, vrw, strings.NewReader(string(val)))
	}
	return nil, fmt.Errorf(`"%v" cannot convert value "%v" of type "%T" as it is invalid`, ti.String(), v, v)
}

// Equals implements TypeInfo interface.
func (ti *varBinaryType) Equals(other TypeInfo) bool {
	if other == nil {
		return false
	}
	if ti2, ok := other.(*varBinaryType); ok {
		return ti.sqlBinaryType.MaxCharacterLength() == ti2.sqlBinaryType.MaxCharacterLength()
	}
	return false
}

// FormatValue implements TypeInfo interface.
func (ti *varBinaryType) FormatValue(v types.Value) (*string, error) {
	if val, ok := v.(types.Blob); ok {
		resStr, err := fromBlob(val)
		if err != nil {
			return nil, err
		}
		return (*string)(unsafe.Pointer(&resStr)), nil
	}
	if _, ok := v.(types.Null); ok || v == nil {
		return nil, nil
	}
	return nil, fmt.Errorf(`"%v" cannot convert NomsKind "%v" to a string`, ti.String(), v.Kind())
}

// GetTypeIdentifier implements TypeInfo interface.
func (ti *varBinaryType) GetTypeIdentifier() Identifier {
	return VarBinaryTypeIdentifier
}

// GetTypeParams implements TypeInfo interface.
func (ti *varBinaryType) GetTypeParams() map[string]string {
	return map[string]string{
		varBinaryTypeParam_Length: strconv.FormatInt(ti.sqlBinaryType.MaxCharacterLength(), 10),
	}
}

// IsValid implements TypeInfo interface.
func (ti *varBinaryType) IsValid(v types.Value) bool {
	if val, ok := v.(types.Blob); ok {
		if int64(val.Len()) <= ti.sqlBinaryType.MaxByteLength() {
			return true
		}
	}
	if _, ok := v.(types.Null); ok || v == nil {
		return true
	}
	return false
}

// NomsKind implements TypeInfo interface.
func (ti *varBinaryType) NomsKind() types.NomsKind {
	return types.BlobKind
}

// Promote implements TypeInfo interface.
func (ti *varBinaryType) Promote() TypeInfo {
	return &varBinaryType{ti.sqlBinaryType.Promote().(sql.StringType)}
}

// String implements TypeInfo interface.
func (ti *varBinaryType) String() string {
	return fmt.Sprintf(`VarBinary(%v)`, ti.sqlBinaryType.MaxCharacterLength())
}

// ToSqlType implements TypeInfo interface.
func (ti *varBinaryType) ToSqlType() sql.Type {
	return ti.sqlBinaryType
}

// fromBlob returns a string from a types.Blob.
func fromBlob(b types.Blob) ([]byte, error) {
	strLength := b.Len()
	if strLength == 0 {
		return []byte{}, nil
	}
	str := make([]byte, strLength)
	n, err := b.ReadAt(context.Background(), str, 0)
	if err != nil && err != io.EOF {
		return []byte{}, err
	}
	if uint64(n) != strLength {
		return []byte{}, fmt.Errorf("wanted %d bytes from blob for data, got %d", strLength, n)
	}

	// For very large byte slices, the standard method of converting a byte slice to a string using "string(str)" will
	// cause it to duplicate the entire string. This uses a lot more memory and significantly impact performance.
	// Using an unsafe pointer, we can avoid the duplication and get a fairly large performance gain. In some unofficial
	// testing, performance improved by 40%.
	// This is inspired by Go's own source code in strings.Builder.String(): https://golang.org/src/strings/builder.go#L48
	// This is also marked as a valid strategy in unsafe.Pointer's own method documentation.
	return str, nil
}

// hasPrefix finds out if a Blob has a prefixed integer. Initially blobs for varBinary prepended an integer indicating
// the length, which was unnecessary (as the underlying sequence tracks the total size). It's been removed, but this
// may be used to see if a Blob is one of those older Blobs. A false positive is possible, but EXTREMELY unlikely.
func hasPrefix(b types.Blob, ctx context.Context) (bool, error) {
	blobLength := b.Len()
	if blobLength < 8 {
		return false, nil
	}
	countBytes := make([]byte, 8)
	n, err := b.ReadAt(ctx, countBytes, 0)
	if err != nil {
		return false, err
	}
	if n != 8 {
		return false, fmt.Errorf("wanted 8 bytes from blob for count, got %d", n)
	}
	prefixedLength := binary.LittleEndian.Uint64(countBytes)
	if prefixedLength == blobLength-8 {
		return true, nil
	}
	return false, nil
}

// varBinaryTypeConverter is an internal function for GetTypeConverter that handles the specific type as the source TypeInfo.
func varBinaryTypeConverter(ctx context.Context, src *varBinaryType, destTi TypeInfo) (tc TypeConverter, needsConversion bool, err error) {
	switch dest := destTi.(type) {
	case *bitType:
		return func(ctx context.Context, vrw types.ValueReadWriter, v types.Value) (types.Value, error) {
			if v == nil || v == types.NullValue {
				return types.NullValue, nil
			}
			blob, ok := v.(types.Blob)
			if !ok {
				return nil, fmt.Errorf("unexpected type converting blob to %s: %T", strings.ToLower(dest.String()), v)
			}
			val, err := fromBlob(blob)
			if err != nil {
				return nil, err
			}
			newVal, err := strconv.ParseUint(string(val), 10, int(dest.sqlBitType.NumberOfBits()))
			if err != nil {
				return nil, err
			}
			return types.Uint(newVal), nil
		}, true, nil
	case *blobStringType:
		return wrapIsValid(dest.IsValid, src, dest)
	case *boolType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *datetimeType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *decimalType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *enumType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *floatType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *geomcollType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *geometryType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *inlineBlobType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *intType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *jsonType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *linestringType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *multilinestringType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *multipointType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *multipolygonType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *pointType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *polygonType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *setType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *timeType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *uintType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *uuidType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *varBinaryType:
		return wrapIsValid(dest.IsValid, src, dest)
	case *varStringType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	case *yearType:
		return wrapConvertValueToNomsValue(dest.ConvertValueToNomsValue)
	default:
		return nil, false, UnhandledTypeConversion.New(src.String(), destTi.String())
	}
}
