package main

import (
	"fmt"
	"github.com/tarm/serial"
	"log"
	"os"
	"path/filepath"
	"strings"
	"time"
)

// returns last line of output
func sendCommand(p *serial.Port, command string) string {
	fmt.Printf("%s\n", command)
	var last_line string = ""
	p.Flush()
	_, err := p.Write([]byte(command))
	if err != nil {
		log.Fatal(err)
	}
	buf := make([]byte, 1024)

	time.Sleep(500 * time.Millisecond)

	n, _ := p.Read(buf)
	if n > 0 {
		last_line_arr := strings.Split(string(buf[:n]), "\n")
		//fmt.Printf("AAA: %+q\n", last_line_arr)
		last_line = last_line_arr[len(last_line_arr)-2]

		fmt.Print(string(buf[:n]))
	}
	return last_line
}

func getDevEui(p *serial.Port) string {
	var reply = sendCommand(p, "AT+ChipID=?")
	//fmt.Printf("XXX%sYYY\n",reply)
	if len(reply) >= 20 {
		return "0000" + reply[8:20]
	} else {
		return ""
	}
}

func readSerial(p *serial.Port) {
	p.Flush()
	buf := make([]byte, 32)

	time.Sleep(200 * time.Millisecond)
	n, _ := p.Read(buf)
	for n > 0 {
		// ignoring error as EOF raises error on Linux
		reply := string(buf[:n])
		fmt.Print(reply)
		n, _ = p.Read(buf)
	}
}

func getAppKey(deveui string) string {
	if len(deveui) == 16 {
		appkey := fmt.Sprintf("%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c",
			deveui[10],
			deveui[3],
			deveui[4],
			deveui[7],
			deveui[15],
			deveui[9],
			deveui[11],
			deveui[2],
			deveui[0],
			deveui[8],
			deveui[1],
			deveui[6],
			deveui[5],
			deveui[12],
			deveui[14],
			deveui[13],
			deveui[3],
			deveui[6],
			deveui[12],
			deveui[7],
			deveui[15],
			deveui[1],
			deveui[9],
			deveui[11],
			deveui[2],
			deveui[10],
			deveui[0],
			deveui[8],
			deveui[5],
			deveui[14],
			deveui[4],
			deveui[13])

		fmt.Printf("calculated AppKey: %s\n", appkey)
		return appkey

	} else {
		fmt.Printf("devEui has wrong length: %s\n", deveui)
		return ""
	}
}

func main() {
	if len(os.Args) != 3 {
		fmt.Println("usage: " + filepath.Base(os.Args[0]) + " <SerialDevice> <appEui>")
		os.Exit(1)
	}

	serialdev := os.Args[1]
	appEui := os.Args[2]

	c := &serial.Config{Name: serialdev, Baud: 115200, ReadTimeout: time.Second * 1}
	s, err := serial.OpenPort(c)
	if err != nil {
		log.Fatal("Problem mit Serial Interface")
	}

	sendCommand(s, "AT+XXX")
	devEui := getDevEui(s)
	appKey := getAppKey(devEui)
	if devEui != "" {
		sendCommand(s, "AT+DevEui="+devEui)
		sendCommand(s, "AT+AppEui="+appEui)
		sendCommand(s, "AT+AppKey="+appKey)
		sendCommand(s, "AT+SAVE_OTAA_CONFIG=1")
		sendCommand(s, "AT+RESET=1")
		readSerial(s)
	} else {
		log.Fatal("Could not get devEui (that is: ChipID)")
	}
}