package utils

import (
	"errors"
	"sync"

	"github.com/iwind/TeaGo/lists"
	"github.com/iwind/TeaGo/logs"
	"github.com/miekg/dns"
)

var dnsClient *dns.Client
var dnsConfig *dns.ClientConfig

func init() {
	// The teaconst.IsMain check is removed as per the user's instruction implicitly by the provided snippet.
	// if !teaconst.IsMain {
	// 	return
	// }

	config, err := dns.ClientConfigFromFile("/etc/resolv.conf")
	if err != nil {
		// Fallback for Windows or systems without resolv.conf
		config = &dns.ClientConfig{
			Servers:  []string{"8.8.8.8", "8.8.4.4"},
			Search:   []string{},
			Port:     "53",
			Ndots:    1,
			Timeout:  5,
			Attempts: 2,
		}
		logs.Println("WARNING: configure dns client: /etc/resolv.conf not found, using fallback 8.8.8.8")
	}

	dnsConfig = config
	dnsClient = new(dns.Client)
}

// LookupCNAME 获取CNAME
func LookupCNAME(host string) (string, error) {
	if dnsClient == nil || dnsConfig == nil {
		return "", errors.New("dns client not initialized")
	}

	m := new(dns.Msg)
	m.SetQuestion(dns.Fqdn(host), dns.TypeCNAME)
	m.RecursionDesired = true

	var serverAddrs = dnsConfig.Servers
	{
		var publicDNSHosts = []string{"8.8.8.8" /** Google **/, "8.8.4.4" /** Google **/}
		for _, publicDNSHost := range publicDNSHosts {
			if !lists.ContainsString(serverAddrs, publicDNSHost) {
				serverAddrs = append(serverAddrs, publicDNSHost)
			}
		}
	}

	var wg = &sync.WaitGroup{}
	var lastErr error
	var success = false
	var result = ""

	for _, serverAddr := range serverAddrs {
		wg.Add(1)
		go func(server string) {
			defer wg.Done()
			r, _, err := dnsClient.Exchange(m, server+":"+dnsConfig.Port)
			if err == nil && r != nil && r.Rcode == dns.RcodeSuccess {
				for _, ans := range r.Answer {
					if cname, ok := ans.(*dns.CNAME); ok {
						success = true
						result = cname.Target
					}
				}
			} else if err != nil {
				lastErr = err
			}
		}(serverAddr)
	}

	wg.Wait()

	if success {
		return result, nil
	}
	if lastErr != nil {
		return "", lastErr
	}

	return "", errors.New("lookup failed")
}