package ip

import (
	"net"
	"strings"
)

func External() (res []string) {
	var (
		err    error
		addrs  []net.Addr
		inters []net.Interface
	)
	if inters, err = net.Interfaces(); err != nil {
		return
	}
	for _, inter := range inters {
		if !strings.HasPrefix(inter.Name, "lo") {
			if addrs, err = inter.Addrs(); err != nil {
				continue
			}
			for _, addr := range addrs {
				if ipNet, ok := addr.(*net.IPNet); ok {
					if ipNet.IP.IsLoopback() || ipNet.IP.IsLinkLocalMulticast() || ipNet.IP.IsLinkLocalUnicast() {
						continue
					}
					if ip4 := ipNet.IP.To4(); ip4 != nil {
						switch true {
						case ip4[0] == 10:
							continue
						case ip4[0] == 172 && ip4[1] >= 16 && ip4[1] <= 31:
							continue
						case ip4[0] == 192 && ip4[1] == 168:
							continue
						default:
							res = append(res, ipNet.IP.String())
						}
					}
				}
			}
		}
	}
	return
}