package packet

type Packer interface {
	// Pack 从原始raw bytes创建一个用于网络传输的 packet.Packet 结构
	Pack(typ Type, data []byte) ([]byte, error)

	// Unpack 解包
	Unpack(data []byte) (*Packet, error)
}

type DefaultPacker struct {
}

// Codec constants.
const (
	headLength    = 4
	maxPacketSize = 64 * 1024
)

func NewDefaultPacker() Packer {
	return &DefaultPacker{}
}

func (d *DefaultPacker) Pack(typ Type, data []byte) ([]byte, error) {
	if typ < Handshake || typ > Kick {
		return nil, ErrWrongPacketType
	}

	p := &Packet{Type: typ, Length: uint32(len(data))}
	buf := make([]byte, p.Length+headLength)

	// header
	buf[0] = byte(p.Type)
	copy(buf[1:headLength], d.intToBytes(p.Length))

	// body
	copy(buf[headLength:], data)

	return buf, nil
}

// Encode packet data length to bytes(Big end)
func (d *DefaultPacker) intToBytes(n uint32) []byte {
	buf := make([]byte, 3)
	buf[0] = byte((n >> 16) & 0xFF)
	buf[1] = byte((n >> 8) & 0xFF)
	buf[2] = byte(n & 0xFF)
	return buf
}

func (d *DefaultPacker) Unpack(data []byte) (*Packet, error) {
	// header
}