package vip

import (
	"fmt"
	"net"

	"github.com/mdlayher/arp"
	"github.com/mdlayher/ethernet"
)

func sendARP(ip net.IP, iface *net.Interface) error {
	c, err := arp.Dial(iface)
	if err != nil {
		return err
	}
	for _, op := range []arp.Operation{arp.OperationRequest, arp.OperationReply} {
		pkt, err := arp.NewPacket(op, iface.HardwareAddr, ip, ethernet.Broadcast, ip)
		if err != nil {
			return fmt.Errorf("assembling %q gratuitous packet for %q: %s", op, ip, err)
		}
		if err = c.WriteTo(pkt, ethernet.Broadcast); err != nil {
			return fmt.Errorf("writing %q gratuitous packet for %q: %s", op, ip, err)
		}
	}
	return nil
}

func ARPSendGratuitous(cidr, iface string) error {
	i, err := net.InterfaceByName(iface)
	if err != nil {
		return fmt.Errorf("failed to get interface %q: %v", iface, err)
	}
	ip, _, err := net.ParseCIDR(cidr)
	if err != nil {
		return fmt.Errorf("failed to parse cidr: %s", cidr)
	}
	return sendARP(ip, i)
}