Code snippet to demonstrate Promises.

gistfile1.js

'use strict';

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

module.exports = function(Events) {
    Events.cancel = function(data, options) {
        return Promise.try(function() {
            var eventIds = data.eventIds;
            var partnerId = options.context.partnerId;
            var userId = options.context.userId;
            var userType = options.context.userType;
            
            if (userType === "practitioner") { // ===. not ==
                var practitionerId = userId;
            } else {
                var practitionerId = data.practitionerId;
            }
            
            return Promise.each(eventIds, function(eventId) {
                // assumes that all of the below returns a promise. if not, you need to promisify.
                return Promise.all([
                    dataProvider.events.exists(eventId, options),
                    practitioners.exists({
                        userId: practitionerId,
                        partnerId: partnerId
                    }, options)
                ]).spread(function(event, practitioner) {
                    Promise.try(function() {
                        // only happens when the previous three calls all succeeded
                        return Promise.all([
                            dataProvider.events.edit(eventId, {status: "cancelled"}, options),
                            patients.exists(event.patientId, options)
                        ]);
                    }).spread(function(editResult, patient) {
                        var message =  "Dear " +  patient.firstName + "," + " " +
                            "your appointment with " +
                            "Dr. " + practitioner.practGivenName + " " +
                            "at " + event.location + " " +
                            "has been CANCELLED for " + 
                            moment(event.start).utcOffset(+330).format('MMMM DD YYYY h:mm a')  +  
                            ".";
                        
                        return messaging.sendMessage({
                            message: message,
                            number: "+" + patient.phoneNumber
                        });
                    }).then(function(response){
                        if (response.statusCode !== 200) {
                            throw new Error("Non-200 status code received (" + response.statusCode + ")")
                        }
                    });
                })
            }).then(function() {
                return {
                    message: "Marked event as cancelled"
                };
            });
        });
    }
};