package peer

import (
	"encoding/binary"
	"fmt"
	"log"
	"net"
	"net/netip"
	"time"

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

func RunMCReader(g Globals, hp *HolePunch, netName string) {
	for {
		if err := runMCReaderInner(g, hp, netName); err != nil {
			log.Printf("[MCReader] %v", err)
		}
		time.Sleep(broadcastErrorTimeoutInterval)
	}
}

func runMCReaderInner(g Globals, hp *HolePunch, netName string) error {
	conn, err := net.ListenMulticastUDP("udp", nil, multicastAddr)
	if err != nil {
		return fmt.Errorf("bind: %w", err)
	}
	defer conn.Close()

	buf := make([]byte, 64)
	for {
		conn.SetReadDeadline(time.Now().Add(32 * time.Second))
		n, src, err := conn.ReadFromUDPAddrPort(buf)
		if err != nil {
			return fmt.Errorf("read: %w", err)
		}
		if n != beaconLen {
			continue
		}
		handleBeacon(g, hp, netName, buf[:n], src)
	}
}

func handleBeacon(g Globals, hp *HolePunch, netName string, beacon []byte, src netip.AddrPort) {
	peerIPByte := beacon[0]
	if peerIPByte == g.LocalPeerIP {
		return
	}

	pubKey, err := wgtypes.NewKey(beacon[1:33])
	if err != nil {
		return
	}

	// Skip relay peers: probing would replace their /24 AllowedIPs with empty.
	if state, err := loadNetworkState(netName); err == nil {
		if p := state.Peers[peerIPByte]; p != nil && p.Relay {
			return
		}
	}

	wgPort := binary.BigEndian.Uint16(beacon[33:35])
	endpoint := netip.AddrPortFrom(src.Addr().Unmap(), wgPort)

	hp.OnEndpointLearned(peerIPByte, pubKey, endpoint, false)
}