Code snippet to demonstrate Promises.

gistfile1.txt

'use strict';

var _            = require('lodash'),
    async        = require('async'),
    moment        = require('moment'),
    messaging     = require('../../messaging'),
    patients      = require('../patients'),
    practitioners = require('../practitioners'),
    dataProvider = require('../../database');

module.exports = function(Events) {
    Events.cancel = function (data, options, cb) {
	var eventIds,
	    partnerId,
	    practitionerId,
	    userId,
	    userType;

	eventIds   = data.eventIds;
	partnerId  = options.context.partnerId;
	userId     = options.context.userId;
	userType   = options.context.userType;

	if(userType == "practitioner") {
	    practitionerId = userId;
	}
	else {
	    practitionerId = data.practitionerId;
	}

	async.each(eventIds, function(eventId, cb) {

	    var eventInfo;
	    async.waterfall([
		function(next) {
		    dataProvider.events.exists(eventId, options, next);
		},

		function(event, next) {
		    eventInfo = event;

		    var filter = { 'userId': practitionerId,
				   'partnerId': partnerId
				 };
		    practitioners.exists(filter, options, next);
		},

		function(practitioner, next) {
		    eventInfo.practInfo = practitioner;

		    var status =  {"status": "cancelled"};
		    dataProvider.events.edit(eventId, status, options, next);
		},

		function(status, next) {
		    patients.exists(eventInfo.patientId, options, next);
		},

		function(patientInfo, next) {
		    eventInfo.patientInfo = patientInfo;
		    next();
		},

		function(next) {
		    var message =  "Dear " +  eventInfo.patientInfo.firstName + "," + " " +
				   "your appointment with " +
				   "Dr. " + eventInfo.practInfo.practGivenName + " " +
				   "at " + eventInfo.location + " " +
				   "has been CANCELLED for " + 
			           moment(eventInfo.start).utcOffset(+330).format('MMMM DD YYYY h:mm a')  +  
			           ".";
				   
		    var options = {
		    "message": message,
		    "number": "+" + eventInfo.patientInfo.phoneNumber
		};
		    messaging.sendMessage(options,  function(err, response) {
			if (err) {
			    return next(err, null);
			}

			if (response.statusCode !== 200) {
			    return next(err, null);
			}
			next(null, eventInfo);
		    });
		}
	    ], cb);
	}, function(err, result) {
	    if (err)
		return cb(err);

	    return cb(null, {"message": "Marked event as cancelled"});
	});
    };
};