package main

import (
	"fmt"
	"io"
	"net"
)

var whitelist []string

func main() {
	ln, err := net.Listen("tcp", ":8080")

	if err != nil {
		fmt.Println("Errur on Listening")
	} else {
		for {
			conn, err := ln.Accept()
			if err != nil {
				fmt.Println("Errur on Accepting")
			} else {
				go handle(conn)
			}
		}
	}
}

func handle(c net.Conn) {
	host, _, _ := net.SplitHostPort(c.RemoteAddr().String())

	io.WriteString(c, "Knock Knock, ")
	io.WriteString(c, host)
	io.WriteString(c, ". ")

	if is_whitelisted(host) {
		io.WriteString(c, "You're whitelisted.")
	} else {
		io.WriteString(c, "You're not whitelisted.")
	}

	add_to_whitelist(host)

	c.Close()
}

func add_to_whitelist(addr string) {
	if ! is_whitelisted(addr) {
		whitelist = append(whitelist, addr)
	}
}

func is_whitelisted(addr string) bool {
	for i:=0; i < len(whitelist); i++ {
		if whitelist[i] == addr {
			return true
		}
	}

	return false
}