package main

import (
	"crypto/hmac"
	"crypto/sha256"
	"encoding/base64"
	"fmt"
	"log"
	"os"
	"regexp"
	"strconv"
	"text/template"
	"time"
)

func main() {
	if len(os.Args) != 2 {
		log.Println("Missing connection string. Example connection string: ostName=saas-iothub-efdc1876-f747-4f6e-95d9-3030c59cc739.azure-devices.net;DeviceId=cMT-8e95;SharedAccessKey=TLhzGZpFZmrAQGWCvBEroxozwSngep82bRikqehfTgg=")
		log.Println("Usage: get-mqtt-params.exe <connection string>")
		return
	}
	connString := os.Args[1]
	// log.Println("Connection string: " + connString)
	re := regexp.MustCompile("HostName=(.*?);DeviceId=(.*?);SharedAccessKey=(.*?)$")
	match := re.FindStringSubmatch(connString)
	if match == nil {
		log.Fatal("Connection string uses a different format?")
	}
	hostname := match[1]
	deviceId := match[2]
	sharedAccessKeyEncoded := match[3]
	sharedAccessKey, err := base64.StdEncoding.DecodeString(sharedAccessKeyEncoded)
	if err != nil {
		log.Fatal(err)
	}

	SaS := createSharedAccessToken(hostname+"/devices/"+deviceId, sharedAccessKey)

	fmt.Printf("# Azure Connection Information\n")
	fmt.Printf("Cloud service: Normal\n")
	fmt.Printf("Protocol:      MQTT v3.1.1\n")
	fmt.Printf("Domain name:   %v\n", hostname)
	fmt.Printf("Port:          8883\n")
	fmt.Printf("Client ID:     %v\n", deviceId)
	fmt.Printf("Username:      %v\n", hostname+"/"+deviceId)
	fmt.Printf("Password:      %v\n", SaS)
	fmt.Printf("Pub. Topic:    %v\n", "devices/"+deviceId+"/messages/events/")
	fmt.Printf("Sub. Topic:    %v\n", "devices/"+deviceId+"/messages/devicebound/#")

	fmt.Printf("[v] Customize length for client ID/username/password\n")
	fmt.Printf("[v] TLS/SSL\n")
	fmt.Printf("[ ] System Topic(s)\n")
}

func createSharedAccessToken(uri string, saKey []byte) string {

	if len(uri) == 0 || len(saKey) == 0 {
		return "Missing required parameter"
	}

	encoded := template.URLQueryEscaper(uri)
	now := time.Now().Unix()
	tenYear := 60 * 60 * 24 * 365 * 10
	ts := now + int64(tenYear)
	// week := 60 * 60 * 24 * 7
	// ts := now + int64(week)
	signature := encoded + "\n" + strconv.Itoa(int(ts))
	hmac := hmac.New(sha256.New, saKey)
	hmac.Write([]byte(signature))
	hmacString := template.URLQueryEscaper(base64.StdEncoding.EncodeToString(hmac.Sum(nil)))

	result := "SharedAccessSignature sr=" + encoded + "&sig=" +
		hmacString + "&se=" + strconv.Itoa(int(ts))
	return result
}