package utils

import (
	"net"

	"github.com/go-errors/errors"
)

func getLocalIP() (net.IP, error) {
	conn, err := net.Dial("udp", "1.0.0.1:53")
	if err != nil {
		return nil, err
	}
	defer conn.Close()

	host, _, err := net.SplitHostPort(conn.LocalAddr().String())
	if err != nil {
		return nil, errors.Wrap(err, 0)
	}
	ip := net.ParseIP(host)
	if ip == nil {
		return nil, errors.Errorf("failed to parse IP address %q", host)
	}
	return ip, nil
}

func FindDefaultAdapter() (*net.Interface, error) {
	localIP, err := getLocalIP()
	if err != nil {
		return nil, errors.WrapPrefix(err, "failed to get local address", 0)
	}

	iflist, err := net.Interfaces()
	if err != nil {
		return nil, errors.WrapPrefix(err, "failed to get interface list", 0)
	}
	for _, iface := range iflist {
		addrs, err := iface.Addrs()
		if err != nil {
			continue
		}
		for _, addr := range addrs {
			ipnet, ok := addr.(*net.IPNet)
			if !ok {
				continue
			}
			if localIP.Equal(ipnet.IP) {
				return &iface, nil
			}
		}
	}
	return nil, errors.New("failed to find default adapter")
}