package main

import (
	"bufio"
	"errors"
	"flag"
	"log"
	"net"
	"strconv"
	"strings"
	"time"
)

var PortOutOfRange = errors.New("Port out of allowed range 1-65535")
var isDebug bool

func init() {
	isDebug = false
}

func debug(v ...interface{}) {
	if isDebug {
		msg := make([]interface{}, len(v)+1)
		msg[0] = "[DEBUG]"
		for i, el := range v {
			msg[i+1] = el
		}
		log.Println(msg...)
	}
}

func handleConn(c net.Conn) {
	defer c.Close()
	debug("connection established:", c)
	reader := bufio.NewReader(c)

	for {
		data, err := reader.ReadString('\n')
		debug("Data =>", data)
		if err != nil {
			log.Fatal(err)
		}
		cleanData := strings.TrimSpace(string(data))
		duration, err := time.ParseDuration(cleanData)
		if err != nil {
			log.Fatal(err)
		}
		debug("Duration =>", duration)
		c.Write([]byte("ACK\n"))
		time.Sleep(duration)
	}

	log.Println("connection closed:", c)
}

func parsePort(port int) (string, error) {
	if port < 1 || port > 65535 {
		return "", PortOutOfRange
	}
	return strconv.Itoa(port), nil
}

func main() {
	var address string
	var port int
	flag.StringVar(&address, "addr", "", "The target address or ip")
	flag.IntVar(&port, "port", 0, "The target port")
	flag.BoolVar(&isDebug, "debug", false, "Enable debug logging")
	flag.Parse()

	parsedPort, err := parsePort(port)
	if err != nil {
		log.Fatal(err)
	}
	host := net.JoinHostPort(address, parsedPort)
	server, err := net.Listen("tcp4", host)
	if err != nil {
		log.Fatal(err)
	}
	defer server.Close()

	for {
		c, err := server.Accept()
		if err != nil {
			log.Fatal(err)
		}
		go handleConn(c)
	}
}