package network

import (
	"net"

	"github.com/pkg/errors"
	"github.com/wlynxg/anet"
)

var (
	_, lanA, _ = net.ParseCIDR("10.0.0.0/8")
	_, lanB, _ = net.ParseCIDR("172.16.0.0/12")
	_, lanC, _ = net.ParseCIDR("192.168.0.0/16")
)

func GetLANIPv4Addrs() ([]string, error) {
	ips := make([]string, 0)

	addrs, err := anet.InterfaceAddrs()
	if err != nil {
		return nil, errors.WithStack(err)
	}

	for _, address := range addrs {
		if ipnet, ok := address.(*net.IPNet); ok && !ipnet.IP.IsLoopback() {
			ipv4 := ipnet.IP.To4()
			if ipv4 == nil {
				continue
			}

			isLAN := lanA.Contains(ipv4) || lanB.Contains(ipv4) || lanC.Contains(ipv4)
			if !isLAN {
				continue
			}

			ips = append(ips, ipv4.String())
		}
	}

	return ips, nil
}

func FindPreferredLocalAddress(ips ...net.IP) (string, error) {
	localAddrs, err := anet.InterfaceAddrs()
	if err != nil {
		return "", errors.WithStack(err)
	}

	for _, addr := range localAddrs {
		if ipnet, ok := addr.(*net.IPNet); ok && !ipnet.IP.IsLoopback() {
			for _, ip := range ips {
				if ipnet.Contains(ip) {
					return ip.String(), nil
				}
			}
		}
	}

	return ips[0].String(), nil
}