// Do this as the first thing so that any code reading it knows the right env.

 process.env.BABEL_ENV = "development";
 process.env.NODE_ENV = "development";

 
 // Makes the script crash on unhandled rejections instead of silently
 // ignoring them. In the future, promise rejections that are not handled will
 // terminate the Node.js process with a non-zero exit code.

 process.on("unhandledRejection", err => {

   throw err;
 });
 
 // Ensure environment variables are read.

 require("../config/env");

 const fs = require("fs");
 const chalk = require("react-dev-utils/chalk");
 const webpack = require("webpack");
 const WebpackDevServer = require("webpack-dev-server");
 const clearConsole = require("react-dev-utils/clearConsole");
 const checkRequiredFiles = require("react-dev-utils/checkRequiredFiles");

 const {
   choosePort,
   createCompiler,
   prepareProxy,

   prepareUrls
 } = require("react-dev-utils/WebpackDevServerUtils");
 const openBrowser = require("react-dev-utils/openBrowser");
 const paths = require("../config/paths");
 const configFactory = require("../config/webpack.config");
 const createDevServerConfig = require("../config/webpackDevServer.config");

 
 const useYarn = fs.existsSync(paths.yarnLockFile);
 const isInteractive = process.stdout.isTTY;
 
 // Warn and crash if required files are missing
 if (!checkRequiredFiles([paths.appHtml, paths.appIndexJs])) {
   process.exit(1);
 }
 
 // Tools like Cloud9 rely on this.
 const DEFAULT_PORT = parseInt(process.env.PORT, 10) || 3000;

 const HOST = process.env.HOST || "0.0.0.0";

 
 if (process.env.HOST) {
   console.log(
     chalk.cyan(
       `Attempting to bind to HOST environment variable: ${chalk.yellow(
         chalk.bold(process.env.HOST)
       )}`
     )
   );
   console.log(
     `If this was unintentional, check that you haven't mistakenly set it in your shell.`
   );
   console.log(

     `Learn more here: ${chalk.yellow("https://bit.ly/CRA-advanced-config")}`

   );
   console.log();
 }
 
 // We require that you explictly set browsers and do not fall back to
 // browserslist defaults.

 const { checkBrowsers } = require("react-dev-utils/browsersHelper");

 checkBrowsers(paths.appPath, isInteractive)
   .then(() => {
     // We attempt to use the default port but if it is busy, we offer the user to
     // run on a different port. `choosePort()` Promise resolves to the next free port.
     return choosePort(HOST, DEFAULT_PORT);
   })
   .then(port => {
     if (port == null) {
       // We have not found a port.
       return;
     }

     const config = configFactory("development");
     const protocol = process.env.HTTPS === "true" ? "https" : "http";

     const appName = require(paths.appPackageJson).name;
     const useTypeScript = fs.existsSync(paths.appTsConfig);
     const urls = prepareUrls(protocol, HOST, port);
     const devSocket = {
       warnings: warnings =>

         devServer.sockWrite(devServer.sockets, "warnings", warnings),
       errors: errors => devServer.sockWrite(devServer.sockets, "errors", errors)

     };
     // Create a webpack compiler that is configured with custom messages.
     const compiler = createCompiler({
       appName,
       config,
       devSocket,
       urls,
       useYarn,
       useTypeScript,

       webpack

     });
     // Load proxy config
     const proxySetting = require(paths.appPackageJson).proxy;
     const proxyConfig = prepareProxy(proxySetting, paths.appPublic);
     // Serve webpack assets generated by the compiler over a web server.
     const serverConfig = createDevServerConfig(
       proxyConfig,
       urls.lanUrlForConfig
     );
     const devServer = new WebpackDevServer(compiler, serverConfig);
     // Launch WebpackDevServer.
     devServer.listen(port, HOST, err => {
       if (err) {
         return console.log(err);
       }
       if (isInteractive) {
         clearConsole();
       }

       console.log(chalk.cyan("Starting the development server...\n"));

       openBrowser(urls.localUrlForBrowser);
     });
 

     ["SIGINT", "SIGTERM"].forEach(function(sig) {

       process.on(sig, function() {
         devServer.close();
         process.exit();
       });
     });
   })
   .catch(err => {
     if (err && err.message) {
       console.log(err.message);
     }
     process.exit(1);
   });