dashboard-backend/server.js

const express = require("express");
const http = require("http");
const socketIo = require("socket.io");
const cors = require("cors");
const axios = require("axios");
require("dotenv").config();

const app = express();

const server = http.createServer(app);

let cachedPrices = null;
let lastFetchTime = 0;
const CACHE_DURATION = 30000;

const io = socketIo(server, {
  cors: {
    origin: process.env.CORS_ORIGIN || "*",
    methods: ["GET", "POST"],
  },
});

// ========== (Middleware) ==========

app.use(cors());

app.use(express.json());

// ========== HTTP Route ==========

app.get("/health", (req, res) => {
  res.json({
    status: "OK",
    message: "Server is running",
    timestamp: new Date().toISOString(),
  });
});

// ========== Socket.IO Logic ==========

// Number of clients
let connectedClients = 0;

// Trigger when client connected
io.on("connection", (socket) => {
  connectedClients++;

  console.log(`✅ Client Connected: ${socket.id}`);
  console.log(`📊 Current Number of Clients: ${connectedClients}`);

  // Broadcast to all clients
  io.emit("clientCount", connectedClients);

  // ========== Monitoring client side events ==========

  // Request Data
  socket.on("requestData", async (dataType) => {
    console.log(`📤 Request Data: ${dataType}`);
    const now = new Date();

    try {
      let data;

      if (dataType === "crypto") {
        if (cachedPrices && now - lastFetchTime < CACHE_DURATION) {
          console.log("📦 Use caching data");
          data = cachedPrices;
        } else {
          // Get data from "CoinGecko API"
          const response = await axios.get(
            "https://api.coingecko.com/api/v3/simple/price",
            {
              params: {
                // list of crypto requested to be shown
                ids: "bitcoin,ethereum,cardano,solana,ripple",
                vs_currencies: "usd",
                include_market_cap: true,
                include_24hr_vol: true,
                include_24hr_change: true,
              },
            }
          );

          // Construct data format
          data = {
            type: "crypto",
            timestamp: new Date(),
            prices: response.data,
          };

          // Update Caches
          cachedPrices = data;
          lastFetchTime = now;
          console.log("✅ Cached New Data");
        }
      }

      // Emit data to client side
      socket.emit("data", data);
      console.log(`✅ Data sent to client: ${socket.id}`);
    } catch (error) {
      console.error("❌ Error on Getting Data:", error.message);
      // Emit Error message to client side
      socket.emit("error", {
        message: "Failed to fetch data",
        details: error.message,
      });
    }
  });

  // ========== Push Data by interval ==========

  // Push every 5 seconds
  const dataInterval = setInterval(async () => {
    try {
      const now = new Date();

      if (cachedPrices && now - lastFetchTime < CACHE_DURATION) {
        socket.emit("data", cachedPrices);
        console.log(`[${now.toISOString()}]📦 Push Cached Data`);
        return;
      }
      // Get latest data
      const response = await axios.get(
        "https://api.coingecko.com/api/v3/simple/price",
        {
          params: {
            ids: "bitcoin,ethereum,cardano,solana,ripple",
            vs_currencies: "usd",
            include_market_cap: true,
            include_24hr_vol: true,
            include_24hr_change: true,
          },
        }
      );

      const data = {
        type: "crypto",
        timestamp: new Date(),
        prices: response.data,
      };

      cachedPrices = data;
      lastFetchTime = now;

      socket.emit("data", data);
    } catch (error) {
      console.error("❌ Error on pushing:", error.message);
    }
  }, CACHE_DURATION); // run every 30 seconds

  // ========== Client Disconnected ==========

  // Trigger when client disconnected
  socket.on("disconnect", () => {
    connectedClients--;
    console.log(`❌ Client Disconnected: ${socket.id}`);
    console.log(`📊 Current Number of Clients: ${connectedClients}`);

    // Broadcast number of clients
    io.emit("clientCount", connectedClients);

    // Clear client's interval
    clearInterval(dataInterval);
  });
});

// ========== Start service ==========

const PORT = process.env.PORT || 5000;

server.listen(PORT, () => {
  console.log("");
  console.log("═══════════════════════════════════════");
  console.log(`✅ Server running on: http://localhost:${PORT}`);
  console.log("📡 WebSocket ready to connect");
  console.log("🔗 CORS Source:", process.env.CORS_ORIGIN || "*");
  console.log("═══════════════════════════════════════");
  console.log("");
});

// ========== Error Handling ==========

// Exception Handling
process.on("unhandledRejection", (err) => {
  console.error("❌ Exceptions:", err);
});

process.on("uncaughtException", (err) => {
  console.error("❌ Exceptions:", err);
  process.exit(1);
});