// mdns-sync.js
// A single-file mDNS sync tool acting as client or server
// Uses mdns-server for mDNS and Express for HTTP


/*********************************
*
*   1. LIBRARY FUNCTIONS
*
*********************************/

//  0. HELPER FUNCTIONS
function convertBufferToString(a) {if (a.data) for (i in a.data) a.data[i] = a.data[i].toString(); return a;}

// 1. Database functions
function saveDbToFile(data, filename) {return fs.writeFileSync(filename,typeof data === 'object'?JSON.stringify(data):data);}
function loadDbFromFile(filename) {if (!fs.existsSync(filename)) return {local:{},remote:{}}; else return JSON.parse(fs.readFileSync(filename));}

// 2. Network functions
function getLocalNetworkAddressesIPs() {
	const os = require('os');

	const interfaces = os.networkInterfaces();
	const addresses = [];

	for (const name of Object.keys(interfaces)) {
	    for (const iface of interfaces[name]) {
	        if (iface.family === 'IPv4' && !iface.internal) {
	            addresses.push(iface.address);
	        }
	    }
	}
	return addresses;
	
}

function sniffmDNSLocalPackets() {

	// 1. Listen for responses
	mdns.on('response', function(response) {
	  // console.log("got a new mDNS response.",response);
	  for (k in response.answers) {
		  let answer = response.answers[k];
		  
		  // 1. Handle DEVICES for a given SERVICE
		  if (answer.type == "PTR") {
			  // 1.1 Filter by RELEVANT SERVICE TYPES
			  if (!["in-addr.arpa","_googlecast._tcp.local","_tcp.local"].some(suffix => answer.name.endsWith(suffix))) return;
			  
			  // 1.2 Initialize POINTERS (services) sub-database
			  if (!db.local.PTR) db.local.PTR = {};
  
			  // 1.3 Initialize this SERVICE TYPE (e.g. _googlecast._tcp.local), if needed
			  if (!db.local.PTR[answer.name]) {
			  	  db.local.PTR[answer.name] = [answer.data];
			  }	else {
				  // Add a new DEVICE to this SERVICE TYPE if needed
				  if (!db.local.PTR[answer.name].includes(answer.data)) 
					  db.local.PTR[answer.name].push(answer.data);
			  }		  	
		  }
		  // 2. Handle DEVICE IP resolution
		  if (answer.type == "A") {
			  // 2.1 Initialize ADDRESSES sub-database
			  if (!db.local.A) db.local.A = {};
			  db.local.A[answer.name] = answer.data;		  	
		  }
		  
		  if (["TXT","SRV"].includes(answer.type)) {
			  // Initialize this device / entry, if needed
			  if (db.local[answer.name] === undefined) db.local[answer.name] = {"TXT":null,"SRV":null};
			  
			  db.local[answer.name][answer.type] = answer.data;
		  }
		  saveDbToFile(db,DB_FILENAME);
	  }
	})

	// 2. Listen for queries
	mdns.on('query', function(query) {/* console.log("query requested",query);*/});

	// 3. Handle the server being destroyed
	mdns.on('destroyed', function () {console.log('Server destroyed.');process.exit(0);});

	// 4. Handle the onReady event
	mdns.on('ready', function () {
		
	  console.log("mDNS server is ready...");
	  // mdns.query({questions:[{ name: '_:googlecast._tcp.local', type: 'PTR', class: 'IN'}]} );
	})

	// initialize the server now that we are watching for events
	mdns.initServer()

}
function injectmDNSPacketLocally(type,name,data,flush = true,_class = 'IN',ttl = 120) { 
	console.log(`sending packet ${name} of ${type} with data: ${data}`);
	mdns.respond({answers:[
		{
			name: name,
			type: type,
			ttl: ttl,
			class: _class,
			flush: flush,
			data: data
		}
]});}



/*********************************
*
*   100. MAIN / IMPERATIVE CODE
*
*********************************/

const fs = require("fs");
const DB_FILENAME = 'database.json';
const db = loadDbFromFile(DB_FILENAME);
const LOCAL_IP_ADDR = getLocalNetworkAddressesIPs()[0];
const mdns = require('mdns-server')({interface: LOCAL_IP_ADDR,reuseAddr: true,loopback: false,noInit: true});
sniffmDNSLocalPackets();

setInterval(function(){
	// INJECT PTR - Pointers services
	for (name in db.remote.PTR) {
		for (i in db.remote.PTR[name])
			injectmDNSPacketLocally('PTR',name,db.remote.PTR[name][i]);
	}
	// INJECT A - Addresses
	for (name in db.remote.A) {
		injectmDNSPacketLocally('A',name,db.remote.A[name]);
	}
	
	
	// INJECT SRV,TXT
	for (name in db.remote) {
		if (["PTR","A"].includes(name)) continue;
		if (db.remote[name].SRV !== null) 
			injectmDNSPacketLocally('SRV',name,db.remote[name].SRV);
		if (db.remote[name].TXT !== null) 
			injectmDNSPacketLocally('TXT',name,Buffer.from(db.remote[name].TXT, 'utf8'));

	}
	
	
	
},5000);