package ll

import (
	"encoding/binary"
	"io"
	"sync"
)

const hdrMagic string = "DJR"
const magicSize int = len(hdrMagic)
const remaningHeaderSize int = 3
const hdrSize int = magicSize + remaningHeaderSize

// Encoder writes Messages to an output stream
type Encoder struct {
	w  io.Writer
	mu sync.Mutex
}

// NewEncoder returns a new encoder that writes to w
func NewEncoder(w io.Writer) *Encoder {
	return &Encoder{w: w}
}

// Encode writes the Low-level encoding of m to the stream
func (enc *Encoder) Encode(m *Msg) error {
	enc.mu.Lock()

	if _, err := enc.w.Write([]byte(hdrMagic)); err != nil {
		enc.mu.Unlock()
		return err
	}
	if err := binary.Write(enc.w, binary.BigEndian, uint8(m.Type)); err != nil {
		enc.mu.Unlock()
		return err
	}
	if err := binary.Write(enc.w, binary.BigEndian, uint16(len(m.Data)+hdrSize)); err != nil {
		enc.mu.Unlock()
		return err
	}

	_, err := enc.w.Write(m.Data)
	enc.mu.Unlock()
	return err
}