package iface

import (
	"fmt"
	"slices"

	"github.com/pkg/errors"
)

// format can be: tun0, tun_0, so the prefix should be tun/tun_
func GetAvailableTunName(tunPrefix string) (string, error) {
	ifaces, err := GetIfacesNameByPrefix(tunPrefix)
	if err != nil {
		return "", err
	}
	if len(ifaces) == 0 {
		return fmt.Sprintf("%s%d", tunPrefix, 0), nil
	}

	i := 0
	for ; i < 10; i++ {
		curr := fmt.Sprintf("%s%d", tunPrefix, i)
		if !slices.Contains(ifaces, curr) {
			return curr, nil
		}
	}

	return "", errors.New("no tun iface available")
}

// macos: utun
func GetAvailableUTunName() (string, error) {
	return GetAvailableTunName("utun")
}