const spawn = require('child_process').spawn;
const fs = require('fs');

function debounce(func, wait, immediate) {
  var timeout;
  return function() {
    var context = this, args = arguments;
    var later = function() {
      timeout = null;
      if (!immediate) func.apply(context, args);
    };
    var callNow = immediate && !timeout;
    clearTimeout(timeout);
    timeout = setTimeout(later, wait);
    if (callNow) func.apply(context, args);
  };
};

function fileChanged(_, filename) {
  process.stdout.write('\033[2J'); // CLEAR
  console.log(`main.js changed, reloading...`)
  var child = spawn('node', [filename]);

  child.stdin.pipe(process.stdin);
  child.stdout.pipe(process.stdout);

  child.on('close', (code) => {
    console.log(`child process exited with code ${code}`);
  });

  child.unref()
}

function runOnceThenWatch(filename) {
  fileChanged(null, filename)
  fs.watch(filename, debounce(fileChanged, 100));
}

runOnceThenWatch('main.js')