server.js

const express = require('express');
const nodemailer = require('nodemailer');
const axios = require('axios');
const hbs = require('nodemailer-express-handlebars');

// load environment variables
require('dotenv').config();

const app = express();

// set the view engine
app.set('view engine', 'handlebars');

// define the port
const port = process.env.PORT || 3000;

// getting all the environment variables
const email = process.env.EMAIL;
const password = process.env.PASSWORD;
const serverUrl = process.env.SERVER_URL;
const emailHost = process.env.EMAIL_HOST;
const clientToken = process.env.CLIENT_TOKEN;

// custom constants
const subject = 'CyberManipal | The Tech News You Need';
let mailingList = "";

// custom list of greetings to pick randomly from
const greetingList = [
    "Here's your weekly dose of byte sized cybersecurity news.",
    "Wanna hear about the latest in tech? Read it on CyberManipal.",
    "(sudo apt-get) update yourself with this handout of cybersecurity news.",
    "If you are looking for tech news, look no further.",
    "Glance through curated, informative news from the realms of technology."
]

// get route
app.get("/", (req, res) => {
    res.status(200).send("<h4 style='font-family: sans-serif'>Wait for next Thursday for your newsletter</h4>");
});

// post route
app.post("/", async(req, res) => {
    if(req.headers.auth_key === process.env.AUTH_KEY){
        try {
            // fetch the latest news to be hadned out
            const resNews = await axios.get(`${serverUrl}/api/news?page=0`);
            let latestFive = resNews.data.data.slice(0, 5);
    
            // format the date field and the link field
            latestFive.forEach(news => {
                news.link = `https://cybermanipal.wearemist.in/article/${news._id}`
                let tempDate = new Date(news.date);
                news.date = tempDate.toDateString();
                news.snippet = news.description.split(" ").slice(0, 70).join(" ");
            })
            
            // fetch the subscribers
            const resEmails = await axios.get(`${serverUrl}/api/newsletter`, {
                headers: {
                    "client_token" : clientToken
                }
            });
            subscriberList = resEmails.data.data;
            
            // create the mailing list
            let tempList = [];
            subscriberList.forEach(sub => {
                tempList.push(sub.email)
            });
            mailingList = tempList.join(", ");
        
            // create a transporter object
            const transporter = nodemailer.createTransport({
                host: emailHost, // configure to use your mail host
                port: 465,
                secure: true, // use SSL
                auth: {
                    user: email,
                    pass: password,
                },
            });
    
            // transporter options for hbs
            var options = {
                viewEngine : {
                    extname: '.hbs', // handlebars extension
                    layoutsDir: 'views/email/', // location of handlebars templates
                    defaultLayout: 'index', // name of main template
                    partialsDir: __dirname + 'views/email/partials/'
                },
                viewPath: 'views/email',
                extName: '.hbs'
            }
    
            // apply hbs config
            transporter.use('compile', hbs(options));
    
            // defining all the email options
            const messageOptions = {
                from: email,
                to: mailingList,
                subject: subject,
                template: 'index',
                context: {
                    news: latestFive,
                    greeting: greetingList[Math.floor(Math.random() * greetingList.length)]
                }
            }
    
            // send the email
            transporter.sendMail(messageOptions, () => {
                // optional callback here
            });
    
            console.log('Emails for ' + new Date().toISOString().slice(0, 10) + ' sent successfully');
            res.status(200).send({ message: "Emails sent" });
        } catch (e) {
            console.log(e);
        }
    } else {
        res.status(400).send({ message: "Auth error" });
    }
});

app.listen(port, () => {
    console.log(`Server listening on port ${port}`)
});