Job Scheduler

Server.js

const express = require('express');
const schedule = require('node-schedule');
const { addMinutes, isValid, parseISO } = require('date-fns');
const bodyParser = require('body-parser');

const app = express();
app.use(bodyParser.json()); // for parsing application/json

const port = 3000;

let jobCount = 0;
let nextJobDate = new Date();
let currentJob = null;

function doSomeWork() {
  console.log('Doing some work for job ' + (++jobCount));
}

// Function to schedule a job
function scheduleJob(date) {
  // Cancel the current job if it exists
  if (currentJob) {
    currentJob.cancel();
  }

  nextJobDate = date;
  currentJob = schedule.scheduleJob(date, function(){
    console.log(`Executing job ${jobCount + 1} at ${new Date()}`);

    // Do the work
    doSomeWork();

    // Schedule the next job 10 minutes after this one completes
    let nextDate = addMinutes(new Date(), 10);
    scheduleJob(nextDate);
  });
}

// Schedule the first job 10 minutes from now
let startDate = addMinutes(new Date(), 10);
scheduleJob(startDate);

app.get('/health', (req, res) => {
  res.json({ nextJobDate });
});

app.post('/schedule', (req, res) => {
  const date = parseISO(req.body.date);

  if (!isValid(date)) {
    return res.status(400).send({ error: 'Invalid date' });
  }

  scheduleJob(date);

  res.send({ message: `Job scheduled for ${date}` });
});

app.listen(port, () => {
  console.log(`Server listening at http://localhost:${port}`);
});