package codec

import (
	"encoding/binary"
	"errors"
	"io"

	"github.com/panjf2000/gnet/v2"
)

var ErrIncompletePacket = errors.New("incomplete packet")

const maxBodyLen = 10 * 1024 * 1024 // 业务最大包体长度，按需调整
// TomeeSocketCodec 协议格式:
//
// * 0           4
// * +-----------+
// * |  body len  |
// * +-----------+
// * |           |
// * +           +
// * | body bytes|
// * +           +
// * |  ... ...  |
// * +-----------+
type TomeeSocketCodec struct{}

var _ SocketCodec = (*TomeeSocketCodec)(nil)

func NewTomeeSocketCodec() *TomeeSocketCodec {
	return &TomeeSocketCodec{}

}

func (codec TomeeSocketCodec) Encode(buf []byte) ([]byte, error) {
	bodyLen := len(buf)
	data := make([]byte, 4+bodyLen)

	// 写入4字节的包长度
	binary.BigEndian.PutUint32(data[:4], uint32(bodyLen))
	// 写入包体
	copy(data[4:], buf)

	return data, nil
}

func (codec TomeeSocketCodec) Decode(c gnet.Conn) ([]byte, error) {

	//	handle(c)
	// 先读取4字节的包长度
	lenBuf, err := c.Peek(4)

	if err != nil {
		if errors.Is(err, io.ErrShortBuffer) {
			return nil, ErrIncompletePacket
		}
		return nil, err
	}

	bodyLen := binary.BigEndian.Uint32(lenBuf)

	if bodyLen > maxBodyLen {
		return nil, errors.New("packet body exceeds max length")
	}

	if c.InboundBuffered() < int(bodyLen) {
		return nil, ErrIncompletePacket
	}
	// 提取包体
	body, _ := c.Next(int(bodyLen))

	return body, nil
}