//go:build darwin

package dns

import (
	"bytes"
	"context"
	"fmt"
	"io/fs"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"time"

	"github.com/fsnotify/fsnotify"
	miekgdns "github.com/miekg/dns"
	log "github.com/sirupsen/logrus"
	"k8s.io/apimachinery/pkg/util/sets"
)

// https://github.com/golang/go/issues/12524
// man 5 resolver

var cancel context.CancelFunc
var resolv = "/etc/resolv.conf"

// SetupDNS support like
// service:port
// service.namespace:port
// service.namespace.svc:port
// service.namespace.svc.cluster:port
// service.namespace.svc.cluster.local:port
func (c *Config) SetupDNS(ctx context.Context) error {
	c.usingResolver(ctx)
	_ = exec.Command("killall", "mDNSResponderHelper").Run()
	_ = exec.Command("killall", "-HUP", "mDNSResponder").Run()
	_ = exec.Command("dscacheutil", "-flushcache").Run()
	return nil
}

func (c *Config) usingResolver(ctx context.Context) {
	var clientConfig = c.Config
	var ns = c.Ns

	path := filepath.Join("/", "etc", "resolver")
	if _, err := os.Stat(path); os.IsNotExist(err) {
		if err = os.MkdirAll(path, fs.ModePerm); err != nil {
			log.Errorf("create resolver error: %v", err)
		}
	}
	newConfig := miekgdns.ClientConfig{
		Servers: clientConfig.Servers,
		Search:  []string{},
		Port:    clientConfig.Port,
		Ndots:   clientConfig.Ndots,
		Timeout: clientConfig.Timeout,
	}
	var searchDomain []string
	for _, search := range clientConfig.Search {
		for _, s := range strings.Split(search, ".") {
			if s != "" {
				searchDomain = append(searchDomain, s)
			}
		}
	}
	for _, s := range sets.New[string](searchDomain...).Insert(ns...).UnsortedList() {
		filename := filepath.Join("/", "etc", "resolver", s)
		content, err := os.ReadFile(filename)
		if os.IsNotExist(err) {
			_ = os.WriteFile(filename, []byte(toString(newConfig)), 0644)
		} else if err == nil {
			var conf *miekgdns.ClientConfig
			conf, err = miekgdns.ClientConfigFromReader(bytes.NewBufferString(string(content)))
			if err != nil {
				log.Errorf("Parse resolver %s error: %v", filename, err)
				continue
			}
			conf.Servers = append([]string{clientConfig.Servers[0]}, conf.Servers...)
			err = os.WriteFile(filename, []byte(toString(*conf)), 0644)
			if err != nil {
				log.Errorf("Failed to write resovler %s error: %v", filename, err)
			}
		} else {
			log.Errorf("Failed to read resovler %s error: %v", filename, err)
		}
	}
}

func (c *Config) usingNetworkSetup(ip string, namespace string) {
	networkSetup(ip, namespace)
	var ctx context.Context
	ctx, cancel = context.WithCancel(context.Background())
	go func() {
		ticker := time.NewTicker(time.Second * 10)
		newWatcher, _ := fsnotify.NewWatcher()
		defer newWatcher.Close()
		defer ticker.Stop()
		_ = newWatcher.Add(resolv)
		c := make(chan struct{}, 1)
		c <- struct{}{}
		for {
			select {
			case <-ticker.C:
				c <- struct{}{}
			case /*e :=*/ <-newWatcher.Events:
				//if e.Op == fsnotify.Write {
				c <- struct{}{}
				//}
			case <-c:
				if rc, err := miekgdns.ClientConfigFromFile(resolv); err == nil && rc.Timeout != 1 {
					if !sets.New[string](rc.Servers...).Has(ip) {
						rc.Servers = append(rc.Servers, ip)
						for _, s := range []string{namespace + ".svc.cluster.local", "svc.cluster.local", "cluster.local"} {
							rc.Search = append(rc.Search, s)
						}
						//rc.Ndots = 5
					}
					//rc.Attempts = 1
					rc.Timeout = 1
					_ = os.WriteFile(resolv, []byte(toString(*rc)), 0644)
				}
			case <-ctx.Done():
				return
			}
		}
	}()
}

func toString(config miekgdns.ClientConfig) string {
	var builder strings.Builder
	//	builder.WriteString(`#
	//# macOS Notice
	//#
	//# This file is not consulted for DNS hostname resolution, address
	//# resolution, or the DNS query routing mechanism used by most
	//# processes on this system.
	//#
	//# To view the DNS configuration used by this system, use:
	//#   scutil --dns
	//#
	//# SEE ALSO
	//#   dns-sd(1), scutil(8)
	//#
	//# This file is automatically generated.
	//#`)
	//	builder.WriteString("\n")
	if len(config.Search) > 0 {
		builder.WriteString(fmt.Sprintf("search %s\n", strings.Join(config.Search, " ")))
	}
	for i := range config.Servers {
		builder.WriteString(fmt.Sprintf("nameserver %s\n", config.Servers[i]))
	}
	if len(config.Port) != 0 {
		builder.WriteString(fmt.Sprintf("port %s\n", config.Port))
	}
	builder.WriteString(fmt.Sprintf("options ndots:%d\n", config.Ndots))
	builder.WriteString(fmt.Sprintf("options timeout:%d\n", config.Timeout))
	//builder.WriteString(fmt.Sprintf("options attempts:%d\n", config.Attempts))
	return builder.String()
}

func (c *Config) CancelDNS() {
	if cancel != nil {
		cancel()
	}
	dir := filepath.Join("/", "etc", "resolver")
	_ = filepath.WalkDir(dir, func(path string, d fs.DirEntry, err error) error {
		if d.IsDir() {
			return nil
		}
		content, err := os.ReadFile(path)
		if err != nil {
			return nil
		}
		var conf *miekgdns.ClientConfig
		conf, err = miekgdns.ClientConfigFromReader(bytes.NewBufferString(string(content)))
		if err != nil {
			return nil
		}
		// if not has this dns server, do nothing
		if !sets.New[string](conf.Servers...).Has(c.Config.Servers[0]) {
			return nil
		}
		for i := 0; i < len(conf.Servers); i++ {
			if conf.Servers[i] == c.Config.Servers[0] {
				conf.Servers = append(conf.Servers[:i], conf.Servers[i+1:]...)
				i--
				// remove once is enough, because if same cluster connect to different namespace
				// dns service ip is same
				break
			}
		}
		if len(conf.Servers) == 0 {
			os.Remove(path)
			return nil
		}
		err = os.WriteFile(path, []byte(toString(*conf)), 0644)
		if err != nil {
			log.Errorf("Failed to write resovler %s error: %v", path, err)
		}
		return nil
	})
	//networkCancel()
	c.removeHosts(c.Hosts)
}

/*
➜  resolver sudo networksetup -setdnsservers Wi-Fi 172.20.135.131 1.1.1.1
➜  resolver sudo networksetup -setsearchdomains Wi-Fi test.svc.cluster.local svc.cluster.local cluster.local
➜  resolver sudo networksetup -getsearchdomains Wi-Fi
test.svc.cluster.local
svc.cluster.local
cluster.local
➜  resolver sudo networksetup -getdnsservers Wi-Fi
172.20.135.131
1.1.1.1
*/
func networkSetup(ip string, namespace string) {
	networkCancel()
	b, err := exec.Command("networksetup", "-listallnetworkservices").Output()
	if err != nil {
		return
	}
	services := strings.Split(string(b), "\n")
	for _, s := range services[:len(services)-1] {
		cmd := exec.Command("networksetup", "-getdnsservers", s)
		output, err := cmd.Output()
		if err == nil {
			var nameservers []string
			if strings.Contains(string(output), "There aren't any DNS Servers") {
				nameservers = make([]string, 0, 0)
				// fix networksetup -getdnsservers is empty, but resolv.conf nameserver is not empty
				if rc, err := miekgdns.ClientConfigFromFile(resolv); err == nil {
					nameservers = rc.Servers
				}
			} else {
				nameservers = strings.Split(string(output), "\n")
				nameservers = nameservers[:len(nameservers)-1]
			}
			// add to tail
			nameservers = append(nameservers, ip)
			args := []string{"-setdnsservers", s}
			output, err = exec.Command("networksetup", append(args, nameservers...)...).Output()
			if err != nil {
				log.Warnf("error while set dnsserver for %s, err: %v, output: %s\n", s, err, string(output))
			}
		}
		output, err = exec.Command("networksetup", "-getsearchdomains", s).Output()
		if err == nil {
			var searchDomains []string
			if strings.Contains(string(output), "There aren't any Search Domains") {
				searchDomains = make([]string, 0, 0)
			} else {
				searchDomains = strings.Split(string(output), "\n")
				searchDomains = searchDomains[:len(searchDomains)-1]
			}
			newSearchDomains := make([]string, len(searchDomains)+3, len(searchDomains)+3)
			copy(newSearchDomains[3:], searchDomains)
			newSearchDomains[0] = fmt.Sprintf("%s.svc.cluster.local", namespace)
			newSearchDomains[1] = "svc.cluster.local"
			newSearchDomains[2] = "cluster.local"
			args := []string{"-setsearchdomains", s}
			bytes, err := exec.Command("networksetup", append(args, newSearchDomains...)...).Output()
			if err != nil {
				log.Warnf("error while set search domain for %s, err: %v, output: %s\n", s, err, string(bytes))
			}
		}
	}
}

func networkCancel() {
	b, err := exec.Command("networksetup", "-listallnetworkservices").CombinedOutput()
	if err != nil {
		return
	}
	services := strings.Split(string(b), "\n")
	for _, s := range services[:len(services)-1] {
		output, err := exec.Command("networksetup", "-getsearchdomains", s).Output()
		if err == nil {
			i := strings.Split(string(output), "\n")
			if i[1] == "svc.cluster.local" && i[2] == "cluster.local" {
				bytes, err := exec.Command("networksetup", "-setsearchdomains", s, strings.Join(i[3:], " ")).Output()
				if err != nil {
					log.Warnf("error while remove search domain for %s, err: %v, output: %s\n", s, err, string(bytes))
				}

				output, err := exec.Command("networksetup", "-getdnsservers", s).Output()
				if err == nil {
					dnsServers := strings.Split(string(output), "\n")
					// dnsServers[len(dnsServers)-1]=""
					// dnsServers[len(dnsServers)-2]="ip which added by KubeVPN"
					dnsServers = dnsServers[:len(dnsServers)-2]
					if len(dnsServers) == 0 {
						// set default dns server to 1.1.1.1 or just keep on empty
						dnsServers = append(dnsServers, "empty")
					}
					args := []string{"-setdnsservers", s}
					combinedOutput, err := exec.Command("networksetup", append(args, dnsServers...)...).Output()
					if err != nil {
						log.Warnf("error while remove dnsserver for %s, err: %v, output: %s", s, err, string(combinedOutput))
					}
				}
			}
		}
	}
}

func GetHostFile() string {
	return "/etc/hosts"
}