package models

import (
	"encoding/binary"
	"errors"
)

type Message struct {
	Type    uint16
	Version uint16
	Payload []byte
}

func (m *Message) Encode() []byte {
	payloadLen := len(m.Payload)
	if payloadLen > 0xFFFF {
		return nil
	}

	buf := make([]byte, 8+payloadLen)

	binary.LittleEndian.PutUint16(buf[0:2], m.Type)
	binary.LittleEndian.PutUint16(buf[2:4], m.Version)
	binary.LittleEndian.PutUint16(buf[4:6], uint16(payloadLen))

	copy(buf[8:], m.Payload)
	return buf
}

func Decode(data []byte) (*Message, error) {
	if len(data) < 8 {
		return nil, errors.New("message too short")
	}

	payloadLen := binary.LittleEndian.Uint16(data[4:6])
	if len(data) != int(8+payloadLen) {
		return nil, errors.New("invalid payload length")
	}

	msg := &Message{
		Type:    binary.LittleEndian.Uint16(data[0:2]),
		Version: binary.LittleEndian.Uint16(data[2:4]),
		Payload: make([]byte, payloadLen),
	}

	copy(msg.Payload, data[8:])
	return msg, nil
}