package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"github.com/robfig/cron"
	log "github.com/sirupsen/logrus"
	"github.com/urfave/cli"
	"io/ioutil"
	"net/http"
	"net/smtp"
	"os"
	"os/signal"
	"path"
	"strconv"
	"syscall"
	"time"
)

type Configuration struct {
	Username string   `json:"name"`
	Email    string   `json:"email"`
	GandiKey string   `json:"gandikey"`
	Domains  []string `json:"domains"`
}

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

var (
	configPath   string
	scheduleSpec string
)

var version = "master"
var commit = "unknown"
var date = "unknown"

func main() {

	app := cli.NewApp()
	app.Name = "dnsupdater"
	app.Version = version + " - " + commit + " - " + date
	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/conf.json",
			EnvVar: "CONFIG_PATH",
		},
		cli.IntFlag{
			Name:   "interval, i",
			Usage:  "poll interval (in seconds)",
			Value:  300,
			EnvVar: "DNSUPDATER_POLL_INTERVAL",
		},
		cli.StringFlag{
			Name:   "schedule, s",
			Usage:  "the cron expression which defines when to update",
			EnvVar: "DNSUPDATER_SCHEDULE",
		},
	}

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

func before(c *cli.Context) error {
	if c.GlobalBool("debug") {
		log.SetLevel(log.DebugLevel)
	}

	pollingSet := c.IsSet("interval")
	cronSet := c.IsSet("schedule")

	if pollingSet && cronSet {
		log.Fatal("Only schedule or interval can be defined, not both.")
	} else if cronSet {
		scheduleSpec = c.String("schedule")
	} else {
		scheduleSpec = "@every " + strconv.Itoa(c.Int("interval")) + "s"
	}
	return nil
}

func start(c *cli.Context) error {
	tryLockSem := make(chan bool, 1)
	tryLockSem <- true

	cr := cron.New()
	err := cr.AddFunc(
		scheduleSpec,
		func() {
			select {
			case v := <-tryLockSem:
				defer func() { tryLockSem <- v }()
				if err := update(c); err != nil {
					log.Println(err)
					SendStatusMail(fmt.Sprintf("Error during update process : %s", err))
				}
			default:
				log.Debug("Skipped another update already running.")
			}

			nextRuns := cr.Entries()
			if len(nextRuns) > 0 {
				log.Debug("Scheduled next run: " + nextRuns[0].Next.String())
			}
		})

	if err != nil {
		return err
	}

	log.Info("First run: " + cr.Entries()[0].Schedule.Next(time.Now()).String())
	cr.Start()

	// Graceful shut-down on SIGINT/SIGTERM
	interrupt := make(chan os.Signal, 1)
	signal.Notify(interrupt, os.Interrupt)
	signal.Notify(interrupt, syscall.SIGTERM)

	<-interrupt
	cr.Stop()
	log.Info("Waiting for running update to be finished...")
	<-tryLockSem
	os.Exit(1)
	return nil
}

func update(c *cli.Context) error {
	configPath = c.String("config")

	if confPathExists, _ := exists(configPath); !confPathExists {
		configPath = "./data"
	}

	file, _ := os.Open(path.Join(configPath, "conf.json"))
	defer file.Close()
	decoder := json.NewDecoder(file)
	configuration := Configuration{}
	err := decoder.Decode(&configuration)

	currentIp, err := GetCurrentIp(configuration)
	if err != nil {
		return err
	}
	newIp, err := GetOutboundIP()
	if err != nil {
		return err
	}

	if currentIp == newIp {
		return nil
	}

	Info("Ip has changed %s -> %s", currentIp, newIp)

	for _, domain := range configuration.Domains {
		err = SetCurrentIp(newIp, domain, configuration)
		if err != nil {
			return err
		}
	}

	SendStatusMail(fmt.Sprintf(`Home IP has changed : %s -> %s
Dns updated successfully`, currentIp, newIp))

	return nil
}

func SendStatusMail(messageText string) {
	// user we are authorizing as
	from := "laurent@lehouerou.net"

	// use we are sending email to
	to := "laurent@lehouerou.net"

	// server we are authorized to send email through
	host := "smtp.fastmail.com"

	// Create the authentication for the SendMail()
	// using PlainText, but other authentication methods are encouraged
	auth := smtp.PlainAuth("", from, "c9bd8fb8l4bhs2f8", host)

	// NOTE: Using the backtick here ` works like a heredoc, which is why all the
	// rest of the lines are forced to the beginning of the line, otherwise the
	// formatting is wrong for the RFC 822 style
	message := fmt.Sprintf(`To: "Laurent Le Houerou" <laurent@lehouerou.net>
From: "Laurent Le Houerou" <laurent@lehouerou.net>
Subject: DnsUpdater Status

%s
`, messageText)

	if err := smtp.SendMail(host+":587", auth, from, []string{to}, []byte(message)); err != nil {
		fmt.Println("Error SendMail: ", err)
	} else {
		fmt.Println("Email Sent!")
	}
}

func GetCurrentIp(configuration Configuration) (string, error) {
	url := "https://dns.api.gandi.net/api/v5/domains/lehouerou.net/records/@/A"

	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
}

func SetCurrentIp(newip string, domain string, configuration Configuration) error {
	url := fmt.Sprintf("https://dns.api.gandi.net/api/v5/domains/%s/records/@/A", domain)
	fmt.Println("URL:>", url)

	var str = fmt.Sprintf("{\"rrset_ttl\": %d,\"rrset_values\": [\"%s\"]}", 600, newip)
	fmt.Println("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()

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

func GetOutboundIP() (string, error) {
	url := "https://api.ipify.org"
	req, err := http.NewRequest("GET", url, nil)
	if err != nil {
		return "", err
	}
	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
	}
	return string(body), 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
}

func Info(format string, args ...interface{}) {
	fmt.Printf("\x1b[34;1m%s\x1b[0m\n", fmt.Sprintf(format, args...))
}