Sneaker price tracker using SendGrid and Node.js

index.js

require('dotenv').config()
const SneaksAPI = require('sneaks-api');
const fs = require("fs");
const schedule = require('node-schedule');
const sneaks = new SneaksAPI();
const sgMail = require('@sendgrid/mail');
sgMail.setApiKey(process.env.SENDGRID_API_KEY);
const jsonString = fs.readFileSync("./subscribers.json");
const subscribers = JSON.parse(jsonString);


(async function main() {
    const sneakerMap = await getSneakerMap(subscribers);
    for await (const subscriber of subscribers) {
        if (sneakerMap[subscriber.styleID].price < subscriber.lastResellPrice - 10) {
            notifySubscriber(sneakerMap[subscriber.styleID], subscriber.email);
            subscriber.lastResellPrice = sneakerMap[subscriber.styleID].price;
        }
    }
    fs.writeFileSync("./subscribers.json", JSON.stringify(subscribers));
})()


async function getSneakerMap(subscribers) {
    var sneakerMap = new Object();
    for (const subscriber of subscribers) {
        if (sneakerMap[subscriber.styleID]) continue;
        const sneaker = await sneaksApiFunctionWrapper(subscriber.styleID);
        sneakerMap[subscriber.styleID] = sneaker;
    }
    return sneakerMap;
}

function notifySubscriber(sneaker, email) {
    const msg = {
        to: RECIPIENT_EMAIL, // Change to your recipient
        from: SENDER_EMAIL, // Change to your verified sender
        subject: `Price Drop - ${sneaker.name}`,
        html: createEmailInHTML(sneaker),
    }
    sgMail.send(msg)
        .then((response) => {
            console.log(response[0].statusCode)
            console.log(response[0].headers)
        })
        .catch((error) => {
            console.error(error)
        })
}

function sneaksApiFunctionWrapper(styleID) {
    return new Promise((resolve, reject) => {
        sneaks.getProductPrices(styleID, function (err, product) {
            const lowestResellSite = Object.keys(product.lowestResellPrice).reduce((a, b) => product.lowestResellPrice[a] > product.lowestResellPrice[b] ? a : b);
            const sneaker = {
                name: product.shoeName,
                image: product.thumbnail,
                site: lowestResellSite,
                price: product.lowestResellPrice[lowestResellSite],
                url: product.resellLinks[lowestResellSite],
                styleID: product.styleID
            };
            resolve(sneaker);
        }, (errorResponse) => {
            reject(errorResponse);
        });
    });
}

function createEmailInHTML(sneaker) {
    return `
    <h2> 
        <img style="font-size:14px;display:block;margin-left:auto;margin-right:auto;width:200px; padding-bottom:15px" src="https://raw.githubusercontent.com/druv5319/Sneaks-API/master/Screenshots/Sneaks_Logo.png"/>
    </h2>
    <div style=" margin-left: auto; margin-right: auto;box-sizing:border-box;width:45%; margin-bottom:30px;background:#fdfdfd;border:1px solid #f0f0f0">
        <h2 style="text-align: center; color: black; font-family: 'avenir';">Price Drop - ${sneaker.name}</h2>
        <p>
            <img style="display: block; margin-left: auto; margin-right: auto;" src=${sneaker.image} alt="" width="auto" height="250" />
        </p>
        <h2 style="text-align: center; color: black; font-family: 'avenir';">$${sneaker.price}</h2>
        <p>&nbsp;</p>
        <p style="font-size: 1.5em; color: black; font-family: avenir; text-align: center;">${sneaker.name} has dropped to
            <strong>$${sneaker.price}</strong> on <strong>${sneaker.site}</strong></p>
        <p style="text-align: center;">
            <a href="${sneaker.url}" style="box-sizing:border-box;border-color:#348eda;font-weight:400;text-decoration:none;display:inline-block;margin:0;color:#ffffff;background-color:#348eda;border:solid 1px #348eda;border-radius:2px;font-size:14px;padding:12px 45px; font-weight: 600;">Buy now on ${sneaker.site}</a>
        </p>
    </div>`;
}