package multicast

import (
	"log"
	"net"
	"net/netip"
	"time"

	"golang.zx2c4.com/wireguard/wgctrl/wgtypes"
)

var addr = net.UDPAddrFromAddrPort(netip.AddrPortFrom(
	netip.AddrFrom4([4]byte{224, 0, 0, 157}),
	4560))

func Broadcast(
	selfVPNIP netip.Addr,
	pubKey wgtypes.Key,
	wgPort uint16,
	signKey *[64]byte,
) {
	for {
		broadcastInner(selfVPNIP, pubKey, wgPort, signKey)
		time.Sleep(errorTimeout)
	}
}

func broadcastInner(selfVPNIP netip.Addr, pubKey wgtypes.Key, wgPort uint16, signKey *[64]byte) {
	conn, err := net.ListenMulticastUDP("udp", nil, addr)
	if err != nil {
		log.Printf("[MCBroadcast] bind: %v", err)
		return
	}
	defer conn.Close()

	buf := make([]byte, BufferSize)
	packet := Packet{
		PeerIP:   selfVPNIP.As4()[3],
		WGPubKey: pubKey,
		WGPort:   wgPort,
	}

	// Re-sign on each send so the timestamp is fresh; a stale timestamp would be
	// dropped by receivers' freshness gate.
	send := func() error {
		packet.Timestamp = time.Now().Unix()
		payload := packet.marshal(buf, signKey)
		_, err := conn.WriteToUDP(payload, addr)
		return err
	}

	if err := send(); err != nil {
		log.Printf("[MCBroadcast] write: %v", err)
	}

	for range time.Tick(broadcastInterval) {
		if err := send(); err != nil {
			log.Printf("[MCBroadcast] write: %v", err)
			return
		}
	}
}