'use strict';

var electron = require('electron');
var dns = require('dns-suite');
var ipc = electron.ipcMain;
var win;
var socket;
var mdnsPort = 5353;
var broadcastAddr = '224.0.0.251';
var queryname = '_cloud._tcp.local';

function sendDeviceQuery() {
  var id = require('crypto').randomBytes(2).readUInt16LE();
  var rpacket = {
    header: {
      id: id,
      qr: 0,
      opcode: 0,
      aa: 0,
      tc: 0,
      rd: 0,
      ra: 0,
      res1:  0,
      res2:  0,
      res3:  0,
      rcode: 0,
    },
    question: [
      {
        name: queryname,
        typeName: 'PTR',
        className: 'IN',
      },
    ],
  };

  var buf = dns.DNSPacket.write(rpacket);
  socket.send(buf, mdnsPort, broadcastAddr, function () {
    console.log('sent mDNS query', buf.toString('hex'));
  });
}

function handleAnswer(message/*, rinfo*/) {
  // console.log('received %d bytes from %s:%d', message.length, rinfo.address, rinfo.port);

  var packet;
  try {
    packet = dns.DNSPacket.parse(message);
  } catch (error) {
    // The majority of the packets collected just listening to our local network seem to
    // throw exceptions, so don't bother logging them.
    return;
  }


  // We are only interested in responses
  if (packet.header.qr !== 1) {
    return;
  }
  // And we only want the responses to the question we send (should be sent back in response)
  if (packet.question.length !== 1 || packet.question[0].name !== queryname) {
    return;
  }
  win.webContents.send('deviceFound', packet);
}

function init(window) {
  if (win) {
    console.error("can't initialize device discovery multiple times");
    return;
  }
  win = window;

  socket = require('dgram').createSocket({ type: 'udp4', reuseAddr: true });
  socket.on('message', handleAnswer);

  socket.bind(mdnsPort, function () {
    var addr = this.address();
    console.log('mDNS device discovery bound on %s:%d', addr.address, addr.port);

    socket.setBroadcast(true);
    socket.addMembership(broadcastAddr);
  });

  ipc.on('startDeviceScan', sendDeviceQuery);
}

module.exports = {
  init: init,
};