package peer

import (
	"log"

	"golang.org/x/crypto/nacl/sign"
)

func createLocalDiscoveryPacket(localIP byte, signingKey []byte) []byte {
	h := header{
		SourceIP: localIP,
		DestIP:   255,
	}
	buf := make([]byte, headerSize)
	h.Marshal(buf)
	out := make([]byte, headerSize+signOverhead)
	return sign.Sign(out[:0], buf, (*[64]byte)(signingKey))
}

func headerFromLocalDiscoveryPacket(pkt []byte) (h header, ok bool) {
	if len(pkt) != headerSize+signOverhead {
		return
	}

	h.Parse(pkt[signOverhead:])
	ok = true
	return
}

func verifyLocalDiscoveryPacket(pkt, buf []byte, pubSignKey []byte) bool {
	_, ok := sign.Open(buf[:0], pkt, (*[32]byte)(pubSignKey))
	return ok
}

// ----------------------------------------------------------------------------

type mcWriter struct {
	conn            mcUDPWriter
	discoveryPacket []byte
}

func newMCWriter(conn mcUDPWriter, localIP byte, signingKey []byte) *mcWriter {
	return &mcWriter{
		conn:            conn,
		discoveryPacket: createLocalDiscoveryPacket(localIP, signingKey),
	}
}

func (w *mcWriter) SendLocalDiscovery() {
	if _, err := w.conn.WriteToUDP(w.discoveryPacket, multicastAddr); err != nil {
		log.Printf("[MCWriter] Failed to write multicast UDP packet: %v", err)
	}
}