Parse dates in natural language for Slack Message Menus

parse-dates.js

/* Example payload
{
  name: 'set_due_date',
  value: '',
  callback_id: 'new_task_message',
  team: { id: 'TXXXXXXXX', domain: 'gette' },
  channel: { id: 'CXXXXXXXX', name: 'work' },
  user: { id: 'UXXXXXXXX', name: 'guillegette' },
  action_ts: '1494154614.757129',
  message_ts: '1494138801.457727',
  attachment_id: '2',
  token: '...'
}
*/
const express = require('express');
const router = express.Router();
const chrono = require('chrono-node');
const moment = require('moment-timezone');

router.post('/options', (req, res, next) => {
  if (req.body.name !== 'set_due_date') {
    // You can only set 1 options API url in Slack, so you need to keep this in 
    // mind if you have multiple types of menus
    return next('Not a valid call');
  }
  const userInput = req.body.value;
  
  // The user click for the firt time on the message menu and we are returning 
  // a default list of options.
  if (!userInput) {
    return res.json({options: [
      {value: 'tomorrow', text: 'Tomorrow'},
      {value: 'in 2 days', text: 'In 2 days'},
      {value: 'on monday', text: 'On Monday'},
      {value: 'next week', text: 'Next week'}
    ]});
  }
  
  // Unfortunately, Slack does not provide the user timezone as part of the payload
  // so hopefully you have this information in your database or you can get it
  // using the users.info API endpoint
  const userTimezone = getUserTimezone(req.body.user.id);
  const userLocalTime = moment.tz(userTimezone).toDate();
    
  // chrono.parse('text to parse', 'offset');
  // offset is a Date object representing the user localtime, because tomorrow is not
  // the same if the user is in Sydney or in San Francisco.
  const dateResults = chrono.parse(userInput, userLocalTime);
  
  if (dateResults.length === 0) {
    return res.json({
      options: []
    });
  }
  
  // We iterate over the parsed results and we use moment.js to turn the date object
  // into a nice format https://momentjs.com/docs/#/displaying/
  const dueDates = dateResults.map((result) => {
    const date = result.start.date();
    return {
      value: date.toString(),
      text: moment(date).format('ddd, hA')
    }
  });
  
  return res.json({
    options: dueDates
  });
    
});