server.js

const express = require("express");
const bodyParser = require("body-parser");
const exec = require("child_process").exec;
const app = express();

// To do:
// - Provide user feedback when request received by server
// - Feedback should appear between "Select a Song" and dropdown menu
// - Feedback should appear, then slowly fade away
// - Add pause / stop button and greater controls for host user?
// - Add box showing next few tracks
// - User connects with server, and server pushes command information to other device?
// - Add visualization? Cassette tape turns when audio is playing? Spectrum of signal?
// - Add live, informal user interaction on host screen: "@gmc just queued up some Talking Heads!"
//    - This will add social element, and help ensure users are engaged with app

// app.use(express.static(__dirname + '/public'));
app.use(express.static('public'));

// =================================================================
// =================================================================
// ==== GLOBAL VARIABLES ===========================================
// =================================================================
// =================================================================

const portNumber = 3000;
var trackQueue = [];
var ipDict = {};
var numUsers = 0;
var durString = "";
var isPlaying = false;
var defaultPlaylist = "Indie Party";
var trackLimit = 3;
var cooldownTime = 0.2;
var initTime = new Date().getTime();

// Command-line strings for generating track duration and position information
const durCmd = "spotify status | grep 'Position:' | cut -d ' ' -f 4";

// =================================================================
// =================================================================
// ==== SYSTEM =====================================================
// =================================================================
// =================================================================

// Library allows for easy parsing of HTML data sent from browser
app.use(bodyParser.urlencoded( {
	extended:true
}));

// Set up node HTTP server via express to serve webpages
app.get("/", function(req, res) {

	// Increment number of current users, and log information
	numUsers++;
	console.log("Received HTTP request. " + numUsers + " users served\n");

	// Serve HTML file
	res.sendFile(__dirname + "/public/index.html");
});

// When data is posted
app.post("/", function(req, res) {

	let curTime = new Date().getTime();
	let isValid = true;

	// Get user IP address
	let ip = req.headers['x-forwarded-for'] || req.connection.remoteAddress;

	// =================================================================
	// ==== vv This works, but logic isn't clear =======================
	// ======= Clean it up! ============================================
	// =================================================================

	// If IP address has already requested a track
	if (ip in ipDict && curTime - ipDict[ip][1] > 60000 * cooldownTime) {

		// If user cooldown time has elapsed, reset play count and cooldown
		ipDict[ip][0] = 0;
		ipDict[ip][1] = curTime;
		console.log("Cooldown period complete. " + ip + " reset to " + ipDict[ip][0]);

	}

	// If user still within cooldown time but at track limit, do nothing
	else if (ip in ipDict && ipDict[ip][0] >= trackLimit) {

		// Do nothing
		isValid = false;

	}

	// Otherwise, increment play count by one, set most recent track play time, 
	// and print feedback in console
	else if (ip in ipDict) {

		ipDict[ip][0]++;
		ipDict[ip][1] = curTime;
		console.log(ip + " incremented to " + ipDict[ip][0] + "!");

	}

	// If first request from this IP address, add it to dictionary with play count of 0
	// and current time as last request time
	else {

		ipDict[ip] = [0, curTime];
		console.log(ip + " added to dictionary with value " + ipDict[ip][0] + "!");

	}

	// Play track at start of queue
	if (ipDict[ip][0] < trackLimit) {

		// Add track URI to queue
		trackQueue.push(req.body.myData);

		// Add track to end of queue
		console.log(req.body.myData + " added to position " + trackQueue.length + " in queue");
	}

	else {

		console.log(trackLimit + "-track limit exceeded. " + cooldownTime +" minutes before reset");

	}

	// If only one track in queue, log information and play now
	if (trackQueue.length == 1) {

		// Log message stating selected song will be played immediately
		console.log("\nOne song in queue - playing now\n");

		// Play track at start of queue
		playTrack(trackQueue[0]);

	}

	else {

		// Log current queue details
		console.log("\nCurrent queue:\n");
		console.log(trackQueue);

	}

	// Then respond
	res.send("Data you sent: " + req.body.myData);

});

// Start listening for requests on port number 3000
app.listen(portNumber, function() {
	console.log("\nServer is running on port " + portNumber + "\n");

})

// =================================================================
// =================================================================
// ==== FUNCTIONS ==================================================
// =================================================================
// =================================================================

function manageQueue(dur) {

	console.log("Waiting " + dur/1000 + " seconds before next track");

	queue = setTimeout(() => {

		// Remove 0th track of queue, as this is finished
		trackQueue.shift();

		// If queue is empty, revert to default playlist
		if (trackQueue.length == 0) {

			// Log updated state
			console.log(
				"\nNo songs waiting - playing backup " + defaultPlaylist + " playlist\n");

			// Default playlist to be played
			playPlaylist(defaultPlaylist);

			// Break out of interval loop
			clearInterval(queue);

		}

		// Otherwise, play new 0th track of queue
		else {

			// Play 0th track in queue
			playTrack(trackQueue[0]);

			// Log information of new track and updated queue state
			console.log("\nNow playing: " + trackQueue[0]);
			console.log("\nCurrent queue:\n");
			console.log(trackQueue);

		}

		// Carry out above instructions only once the time, below, has elapsed
	}, dur-1000);
	// }, 10000);

}

function playTrack(trackURI) {

	// Play next track in queue
	runShell("spotify play uri " +  trackURI).then(results => {

		console.log(results)

		runShell(durCmd).then(results => {

			let dur = -1;

			// Split string using ':' as delimiter
			durString = results.split(":");

			// Calculate duration of track in milliseconds
			dur = parseInt(durString[0]) * 60000 + parseInt(durString[1]) * 1000;

			// Log information
			console.log("Track duration: " + results);

			// Start up queue management function
			manageQueue(dur);

		}).catch(e=>{console.log(e)});


	}).catch(e=>{console.log(e)})

}

function playPlaylist(playlistName) {

	// Play next track in queue
	runShell("spotify play list " +  playlistName).then(results => {
		console.log(results)
		}).catch(e=>{console.log(e)})

	// Set isPlaying flag to true
	isPlaying = true;

}

// Function to calculate track duration from command line
function getTrackDuration() {

	let dur = -1;

	// Retrieve duration of track as string
	runShell(durCmd).then(results => {

			// Split string using ':' as delimiter
			durString = results.split(":");

			// Calculate duration of track in milliseconds
			dur = parseInt(durString[0]) * 60000 + parseInt(durString[1]) * 1000;

			// Log information
			console.log("Track duration: " + dur);

		}).catch(e=>{console.log(e)});

	return dur;
}

// Function to run command-line scripts
function runShell(cmd) {

	return new Promise((resolve, reject) => {
		exec(cmd, (error, stdout, stderr) => {
			if (error)
				reject(error);
			else
				resolve(stdout);

		});
	});
}