package main

import (
	"net/http"
	"net"
	"encoding/base32"
	"strings"
	"flag"
	"log"
)

// define tld
var tld = flag.String("tld", "mesh.cat", "The top level domain for our network")

// domainFromIP derives a meshname subdomain for the authoritative DNS server address
func domainFromIP(target net.IP) string {
	host := strings.ToLower(base32.StdEncoding.EncodeToString(target)[0:26])
	domain := host + "." + *tld
	return domain
}

// handle HTTP requests
func handler(w http.ResponseWriter, r *http.Request) {
	// parse query parameters
	params := r.URL.Query()
	ipParam := params.Get("ip")
	// check if the "ip" query parameter is set to "true"
	showIP := ipParam == "true"
	// get client's ip address
	ip, port, err := net.SplitHostPort(r.RemoteAddr)
	_, _ = port, err	
	// check if we're behind a reverse proxy
	xForwardedFor := r.Header.Get("X-Forwarded-For")
	if xForwardedFor != "" {
		ip = xForwardedFor
	}
	parsedIP := net.ParseIP(ip)
	// return domain for IPv6 only
	if parsedIP.To4() == nil {
		if (showIP) {
			w.Write([]byte(ip + "\n"))
			log.Println(ip)
		} else {
			domain := domainFromIP(parsedIP)
			w.Write([]byte(domain + "\n"))
			log.Println(domain)
		}
	} else {
		// set the response status code to 422
		w.WriteHeader(http.StatusUnprocessableEntity)
		w.Write([]byte("ipv4 not supported\n"))
	}
}

func main() {
	// define path
	http.HandleFunc("/", handler)
	// define ip address
	address := flag.String("address", "[::0]", "The interface address to listen on")
	// define port
	port := flag.String("port", "8008", "The port to listen on")
	// parse the command-line arguments
	flag.Parse()
	// construct listening address
	listenAddr := *address + ":" + *port
	print("Listening on address: ", listenAddr, "\n")
	// start server
	http.ListenAndServe(listenAddr, nil)
}