// SPDX-License-Identifier: BSD-3-Clause
//go:build !windows
// +build !windows

package conf

import (
	"os"
	"runtime"
	"strings"

	"github.com/miekg/dns"
)

// Get the DNS configuration, either from /etc/resolv.conf or somewhere else
func GetDNSConfig() (*dns.ClientConfig, error) {
	if runtime.GOOS == "plan9" {
		dat, err := os.ReadFile("/net/ndb")
		if err != nil {
			return nil, err
		}
		return getPlan9Config(string(dat))
	} else {
		return dns.ClientConfigFromFile("/etc/resolv.conf")
	}
}

// Plan 9 stores its network data in /net/ndb, which seems to be formatted a specific way
func getPlan9Config(str string) (*dns.ClientConfig, error) {
	str = strings.ReplaceAll(str, "\n", "")
	spl := strings.FieldsFunc(str, split)
	servers := []string{}
	for _, option := range spl {
		if strings.HasPrefix(option, "dns=") {
			servers = append(servers, strings.TrimPrefix(option, "dns="))
		}
	}

	// TODO: read more about how customizable Plan 9 is
	return &dns.ClientConfig{
		Servers:  servers,
		Search:   []string{},
		Port:     "53",
		Ndots:    1,
		Timeout:  5,
		Attempts: 1,
	}, nil
}

func split(r rune) bool {
	return r == ' ' || r == '\t'
}