package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"github.com/matryer/try"
	log "github.com/sirupsen/logrus"
	"github.com/urfave/cli"
	"gopkg.in/gomail.v2"
	"io/ioutil"
	"net/http"
	"os"
	"path"
	"regexp"
	"time"
)

type Configuration struct {
	Username        string   `json:"name"`
	Email           string   `json:"email"`
	GandiKey        string   `json:"gandikey"`
	Domains         []string `json:"domains"`
	RouterLogin     string   `json:"router_login"`
	RouterPassword  string   `json:"router_password"`
	RouterStatusUrl string   `json:"router_status_url"`
	WanIPRegex      string   `json:"wan_ip_regex"`
	MailSettings    *struct {
		Sender       string   `json:"sender"`
		To           []string `json:"to"`
		SmtpHost     string   `json:"smtp_host"`
		SmtpLogin    string   `json:"smtp_login"`
		SmtpPassword string   `json:"smtp_password"`
		SmtpPort     int      `json:"smtp_port"`
	} `json:"mail_settings"`
}

type DnsResponse struct {
	RecordType string   `json:"rrset_type"`
	Ttl        int      `json:"rrset_ttl"`
	Name       string   `json:"rrset_name"`
	Values     []string `json:"rrset_values"`
}

var (
	configuration *Configuration
	configPath    string
)

const (
	GandiARecordUrl = "https://dns.api.gandi.net/api/v5/domains/%s/records/@/A"
)

func main() {

	app := cli.NewApp()
	app.Name = "dnsupdater"
	app.Usage = "Automatically update dns"
	app.Before = before
	app.Action = start
	app.Flags = []cli.Flag{

		cli.StringFlag{
			Name:   "config, C",
			Usage:  "path to config file",
			Value:  "/config",
			EnvVar: "CONFIG_PATH",
		},
	}

	if err := app.Run(os.Args); err != nil {
		log.Fatal(err)
	}
}

func before(c *cli.Context) error {
	log.SetLevel(log.InfoLevel)

	configPath = path.Join(c.String("config"), "conf.json")
	if confPathExists, _ := exists(configPath); !confPathExists {
		return fmt.Errorf("config file does not exist : %s", configPath)
	}

	file, _ := os.Open(configPath)
	defer file.Close()
	decoder := json.NewDecoder(file)
	configuration = &Configuration{}
	err := decoder.Decode(configuration)
	if err != nil {
		return err
	}
	return nil
}

func start(c *cli.Context) error {
	if err := update(); err != nil {
		SendStatusMail(fmt.Sprintf("Error during update process : %s", err))
		return err
	}
	return nil
}

func update() error {
	newIp, err := GetOutboundIP()
	if err != nil {
		return err
	}

	updatedDomains := ""
	for _, domain := range configuration.Domains {
		currentIp, err := GetCurrentIp(*configuration, domain)
		if err != nil {
			return err
		}

		if currentIp == newIp {
			continue
		}

		log.Infoln(fmt.Sprintf("%s -> Ip has changed %s -> %s", domain, currentIp, newIp))

		err = SetCurrentIp(newIp, domain, *configuration)
		if err != nil {
			return err
		}
		updatedDomains += fmt.Sprintf("\t- %s\n", domain)
	}

	if updatedDomains != "" {
		SendStatusMail(fmt.Sprintf(`Home IP has changed : %s
Dns updated successfully for domains
%s`, newIp, updatedDomains))
	}

	return nil
}

func SendStatusMail(messageText string) {

	settings := configuration.MailSettings
	if settings == nil {
		log.Warnln("no smtp settings defined > status mail not sent")
		return
	}

	d := gomail.NewDialer(settings.SmtpHost, settings.SmtpPort, settings.SmtpLogin, settings.SmtpPassword)
	s, err := d.Dial()
	if err != nil {
		log.Errorln(fmt.Sprintf("error while dialing smtp server : %v", err))
		return
	}

	m := gomail.NewMessage()
	for _, r := range settings.To {
		m.SetHeader("From", settings.Sender)
		m.SetAddressHeader("To", r, "")
		m.SetHeader("Subject", "DnsUpdater Status")
		m.SetBody("text/plain", messageText)

		if err := gomail.Send(s, m); err != nil {
			log.Warnln(fmt.Sprintf("could not send email to %q: %v", r, err))
		}
		m.Reset()
	}
}

func GetCurrentIp(configuration Configuration, domain string) (string, error) {
	var value string
	err := try.Do(func(attempt int) (bool, error) {
		var err error
		value, err = func(configuration Configuration, domain string) (string, error) {
			url := fmt.Sprintf(GandiARecordUrl, domain)
			req, err := http.NewRequest("GET", url, nil)
			if err != nil {
				return "", err
			}
			req.Header.Set("X-Api-Key", configuration.GandiKey)
			client := &http.Client{}
			resp, err := client.Do(req)
			if err != nil {
				return "", err
			}
			defer resp.Body.Close()

			decoder := json.NewDecoder(resp.Body)
			dnsresponse := DnsResponse{}
			err = decoder.Decode(&dnsresponse)
			if err != nil {
				return "", err
			}
			return dnsresponse.Values[0], nil
		}(configuration, domain)
		if err != nil {
			log.Warnln(fmt.Sprintf("Error while getting current ip from gandi : %v", err))
			time.Sleep(30 * time.Second)
		}
		return attempt < 5, err
	})
	if err != nil {
		return "", err
	}
	return value, nil
}

func SetCurrentIp(newip string, domain string, configuration Configuration) error {
	url := fmt.Sprintf(GandiARecordUrl, domain)
	log.Infoln("URL:>", url)

	var str = fmt.Sprintf("{\"rrset_ttl\": %d,\"rrset_values\": [\"%s\"]}", 600, newip)
	log.Infoln("json:", str)
	var jsonStr = []byte(str)
	req, err := http.NewRequest("PUT", url, bytes.NewBuffer(jsonStr))
	if err != nil {
		return err
	}
	req.Header.Set("X-Api-Key", configuration.GandiKey)
	req.Header.Set("Content-Type", "application/json")

	client := &http.Client{}
	resp, err := client.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()

	log.Debugln("response Status:", resp.Status)
	log.Debugln("response Headers:", resp.Header)
	body, _ := ioutil.ReadAll(resp.Body)
	log.Debugln("response Body:", string(body))
	return nil
}

func GetOutboundIP() (string, error) {
	url := configuration.RouterStatusUrl
	if url == "" {
		url = "http://192.168.1.1/Status_Internet.live.asp"
	}
	req, err := http.NewRequest("GET", url, nil)
	if err != nil {
		return "", err
	}
	if configuration.RouterLogin != "" && configuration.RouterPassword != "" {
		req.SetBasicAuth(configuration.RouterLogin, configuration.RouterPassword)
	}
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		return "", err
	}
	defer res.Body.Close()
	body, err := ioutil.ReadAll(res.Body)
	if err != nil {
		return "", err
	}

	log.Debugln(string(body))
	wanipregex := configuration.WanIPRegex
	if wanipregex == "" {
		wanipregex = "wan_ipaddr::([0-9.]*)}"
	}
	r := regexp.MustCompile(wanipregex)
	matches := r.FindStringSubmatch(string(body))
	if len(matches) < 2 {
		return "", fmt.Errorf("unable to find WAN IP with regex %s in %s", wanipregex, string(body))
	}
	return matches[1], nil
}

func exists(path string) (bool, error) {
	_, err := os.Stat(path)
	if err == nil {
		return true, nil
	}
	if os.IsNotExist(err) {
		return false, nil
	}
	return true, err
}