package peer

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

	"vppn/peer/control"
)

var _ ControlConn = (*udpControlConn)(nil)

type udpControlConn struct {
	conn *net.UDPConn
}

// newUDPControlConn opens a UDP socket bound to localIP:port.
func newUDPControlConn(localIP netip.Addr, port uint16) (*udpControlConn, error) {
	addr := net.UDPAddrFromAddrPort(netip.AddrPortFrom(localIP, port))
	conn, err := net.ListenUDP("udp4", addr)
	if err != nil {
		return nil, err
	}
	return &udpControlConn{conn: conn}, nil
}

func (c *udpControlConn) SendPing(dst netip.AddrPort, ping control.Ping, buf []byte) error {
	_, err := c.conn.WriteToUDP(ping.Marshal(buf), net.UDPAddrFromAddrPort(dst))
	return err
}

// run reads incoming ping packets and forwards them to ch until ctx is done.
// Call this in a goroutine before starting the App event loop.
func (c *udpControlConn) run(ch chan<- PingEvent) {
	const errorTimeout = 8 * time.Second

	var buf [control.Size]byte
	for {
		n, src, err := c.conn.ReadFromUDP(buf[:])
		if err != nil {
			log.Printf("control read: %v", err)
			time.Sleep(errorTimeout)
			continue
		}

		if n != control.Size {
			continue
		}

		ping, err := control.Unmarshal(buf)
		if err != nil {
			log.Printf("control unmarshal: %v", err)
			continue
		}

		srcIP, ok := netip.AddrFromSlice(src.IP)
		if !ok {
			continue
		}

		ch <- PingEvent{srcVPNIP: srcIP.Unmap(), ping: ping}
	}
}

func (c *udpControlConn) Close() error {
	return c.conn.Close()
}