Comp-590-project-Strandcast/server.js

require('dotenv').config();
const express = require('express');
const http = require('http');
const { Server } = require("socket.io");
const axios = require('axios');

const app = express();
const server = http.createServer(app);
const io = new Server(server);

app.use(express.static('public'));

// --- Cloudflare Credentials ---
app.get('/api/get-turn-credentials', async (req, res) => {
	try {
		const response = await axios.post(
			`https://rtc.live.cloudflare.com/v1/turn/keys/${process.env.CLOUDFLARE_APP_ID}/credentials/generate-ice-servers`,
			{ ttl: 86400 },
			{ headers: { 'Authorization': `Bearer ${process.env.CLOUDFLARE_API_TOKEN}`, 'Content-Type': 'application/json' } }
		);
		res.json(response.data);
	} catch (error) {
		console.error("Cloudflare Error:", error.message);
		res.status(500).json({ error: "Failed to fetch credentials" });
	}
});

// --- Daisy Chain Logic ---
let strand = []; // Ordered list of socket IDs
let scores = {}; // Map: socket.id -> score (0-100)

io.on('connection', (socket) => {
	console.log(`User connected: ${socket.id}`);

	// Default score for new users (optimistic, so they get a chance to prove themselves)
	scores[socket.id] = 80;

	socket.on('update_score', (score) => {
		scores[socket.id] = score;
	});

	// A. Start Stream (Head)
	socket.on('start_stream', () => {
		if (strand.length > 0) {
			socket.emit('error_msg', "Stream already in progress.");
			return;
		}
		strand.push(socket.id);
		console.log("Stream started. Head:", socket.id);
		socket.emit('role_assigned', 'head');
	});

	// B. Join Stream (Tail)
	socket.on('join_stream', () => {
		if (strand.length === 0) {
			socket.emit('error_msg', "No active stream to join.");
			return;
		}

		const upstreamPeerId = strand[strand.length - 1];
		strand.push(socket.id);

		console.log(`User ${socket.id} joined. Upstream: ${upstreamPeerId}`);

		// 1. Tell Upstream to connect to ME
		io.to(upstreamPeerId).emit('connect_to_downstream', { downstreamId: socket.id });

		// 2. Request Keyframe from Head (Delayed to allow connection setup)
		setTimeout(() => {
			if (strand[0]) io.to(strand[0]).emit('request_keyframe');
		}, 2000);
	});

	// C. Signaling
	socket.on('signal_msg', ({ target, type, sdp, candidate }) => {
		io.to(target).emit('signal_msg', { sender: socket.id, type, sdp, candidate });
	});

	// D. Keyframe Relay
	socket.on('relay_keyframe_upstream', () => {
		// In a real robust app, you'd bubble this up the chain.
		// Here we just blast the Source directly if we know who they are.
		if (strand[0]) io.to(strand[0]).emit('request_keyframe');
	});

	// E. Disconnects (Healing)
	socket.on('disconnect', () => {
		const index = strand.indexOf(socket.id);
		if (index === -1) return;

		console.log(`User ${socket.id} disconnected. Index: ${index}`);

		// Head left
		if (index === 0) {
			strand = [];
			io.emit('stream_ended');
			return;
		}

		// Tail left
		if (index === strand.length - 1) {
			strand.pop();
			return;
		}

		// Middle left (Stitch)
		const upstreamNode = strand[index - 1];
		const downstreamNode = strand[index + 1];
		strand.splice(index, 1);

		console.log(`Healing: ${upstreamNode} -> ${downstreamNode}`);
		io.to(upstreamNode).emit('connect_to_downstream', { downstreamId: downstreamNode });

		setTimeout(() => {
			if (strand[0]) io.to(strand[0]).emit('request_keyframe');
		}, 2000);
	});
});

// --- THE OPTIMIZER LOOP ---
setInterval(() => {
	if (strand.length < 3) return; // Need at least Head + 2 Nodes to swap anything

	// We iterate from the 2nd node (Index 1) to the end.
	// Index 0 is HEAD (Source), we never move the source.
	let swapped = false;

	// We look for ONE swap per cycle to minimize chaos.
	for (let i = 1; i < strand.length - 1; i++) {
		const current = strand[i];
		const next = strand[i + 1];

		const scoreCurrent = scores[current] || 0;
		const scoreNext = scores[next] || 0;

		// THRESHOLD: Only swap if the next guy is significantly stronger (+15 points)
		// This prevents users flip-flopping constantly due to minor fluctuations.
		if (scoreNext > scoreCurrent + 15) {
			console.log(`Swapping Weak ${current} (${scoreCurrent}) with Strong ${next} (${scoreNext})`);

			performSwap(i, i + 1);
			swapped = true;
			break; // Stop after one swap to let network settle
		}
	}
}, 10000); // Run every 10 seconds

function performSwap(indexA, indexB) {
	// 1. Update the Array (Logical Swap)
	const nodeA = strand[indexA];
	const nodeB = strand[indexB];
	strand[indexA] = nodeB;
	strand[indexB] = nodeA;

	// State after swap:
	// [ ... -> Upstream -> NodeB -> NodeA -> Downstream -> ... ]

	// Identify the relevant neighbors
	const upstreamNode = strand[indexA - 1]; // The node before the pair
	const downstreamNode = strand[indexB + 1]; // The node after the pair

	// 2. Instruct the Upstream to connect to the NEW first node (NodeB)
	if (upstreamNode) {
		io.to(upstreamNode).emit('connect_to_downstream', { downstreamId: nodeB });
	}

	// 3. Instruct NodeB to connect to NodeA (The internal link)
	io.to(nodeB).emit('connect_to_downstream', { downstreamId: nodeA });

	// 4. Instruct NodeA to connect to the Downstream (or null if end)
	if (downstreamNode) {
		io.to(nodeA).emit('connect_to_downstream', { downstreamId: downstreamNode });
	} else {
		// If NodeA is now the tail, it disconnects its downstream
		io.to(nodeA).emit('disconnect_downstream'); // You might need to add this handler to client
	}

	// 5. Trigger Keyframes to heal the image
	setTimeout(() => {
		if (strand[0]) io.to(strand[0]).emit('request_keyframe');
	}, 1000);
}



const PORT = process.env.PORT || 3000;
server.listen(PORT, () => console.log(`Server running on http://localhost:${PORT}`));