handler.js

require("dotenv").config();
const jwt = require("jsonwebtoken");
const nodemailer = require("nodemailer");
const nodemailerSendgrid = require("nodemailer-sendgrid");

module.exports.notifier = (event, context, callback) => {
  let verifiedEvent;

  try {
    verifiedEvent = jwt.verify(JSON.parse(event.body).payload, process.env.JWT_SECRET);
  } catch (e) {
    return sendResponse({ statusCode: 401, callback, body: e });
  }

  sendEmail(verifiedEvent)
    .then(info => {
      sendResponse({ statusCode: 200, body: info, callback });
    })
    .catch(error => {
      return sendResponse({ statusCode: 422, body: error, callback });
    });
};

const sendResponse = ({ statusCode, body, callback }) => {
  const response = {
    statusCode,
    headers: {
      "Access-Control-Allow-Origin": "*",
      "Access-Control-Allow-Credentials": true,
    },
    multiValueHeaders: {
      "Access-Control-Allow-Headers": ["Access-Control-Allow-Origin", "Content-Type"],
    },
    body: JSON.stringify(body),
  };
  return callback(null, response);
};

const _smtpConnect = () => {
  return new Promise(resolve => {
    const transporter = nodemailer.createTransport(nodemailerSendgrid({ apiKey: process.env.API_KEY }));
    resolve(transporter);
  });
};

const sendEmail = payload => {
  return _smtpConnect().then(transporter => {
    return new Promise((resolve, reject) => {
      const mailOptions = { ...payload, text: payload.body, html: payload.body };

      transporter.sendMail(mailOptions, (error, info) => {
        if (error) {
          reject(error);
        }
        resolve(info);
      });
    });
  });
};