app.js

import express from "express";
import favicon from "serve-favicon"; // Import serve-favicon
import path from "path"; // Import path module to resolve the path to favicon
import { fileURLToPath } from "url"; // Import fileURLToPath to convert URL to a path
import { config } from "./config/config.js";
import { initializeMiddlewares } from "./middlewares.js";
import { initializeRoutes } from "./route.js";
import { connectDB } from "./config/db.config.js";
import { createServer } from "./server.js";
import { logger } from "./config/logger.config.js";
import { globalErrorHandler } from "./config/globalErrorHandler.js";
import cluster from "cluster";
import os from "os";

// Get the __dirname equivalent in ESM
const __filename = fileURLToPath(import.meta.url);
const __dirname = path.dirname(__filename);

const numCPUs = os.cpus().length; // Get the number of available CPU cores

// Check if clustering should be used (if more than 1 CPU core)
if (numCPUs > 1 && cluster.isPrimary) {
  // If the current process is the primary (master) process
  logger.info(`Primary process ${process.pid} is running`);

  // Fork workers based on the number of CPU cores
  for (let i = 0; i < numCPUs; i++) {
    cluster.fork();
  }

  // Listen for dying workers and fork a new one
  cluster.on("exit", (worker, code, signal) => {
    logger.info(`Worker ${worker.process.pid} died. Forking a new worker...`);
    cluster.fork();
  });
} else {
  // Run in a single process if single-core or non-primary

  const app = express();

  // Use serve-favicon middleware
  app.use(favicon(path.join(__dirname, "public", "favicon.ico")));

  // Initialize middlewares
  initializeMiddlewares(app);

  // Initialize routes
  initializeRoutes(app);

  // Handle 404 errors for undefined routes
  app.use((req, res, next) => {
    logger.warn(`404 Error: ${req.method} ${req.originalUrl}`);
    res.status(404).json({
      status: "fail",
      message: "Resource not found. Please check the URL and try again.",
    });
  });

  // Global error handler (must be registered after routes)
  app.use(globalErrorHandler);

  // Connect to the database and start the server
  connectDB(config.DATABASE_URL)
    .then(() => {
      const server = createServer(app);
      server.listen(config.PORT, () => {
        logger.info(`Server started and running on port ${config.PORT}`);
      });

      // Graceful shutdown handling
      const shutdownHandler = (signal) => {
        logger.info(
          `${signal} signal received: closing HTTP server in worker ${process.pid}`
        );
        server.close(() => {
          logger.info(`HTTP server closed in worker ${process.pid}`);
          process.exit(0);
        });
      };

      process.on("SIGTERM", () => shutdownHandler("SIGTERM"));
      process.on("SIGINT", () => shutdownHandler("SIGINT"));
    })
    .catch((error) => {
      logger.error(
        `MongoDB Connection Error in worker ${process.pid}: ${error.message}`,
        { error }
      );
      process.exit(1);
    });
}