index.js

// Declaring variables and destructuring to get important values
const express = require('express');
const TelegramBot = require('node-telegram-bot-api')
const { getEmailBody } = require('./functions')
const { google } = require('googleapis');
const { OAuth2Client } = require('google-auth-library');
const { port, myChatId, telegramBotToken, oa_clientId, oa_clientSecret, oa_redirectUri, oa_accessType, refreshtime } = require('dotenv').config().parsed

// Declaring instances for express, telegram_bot and oauth2
const app = express();
const bot = new TelegramBot(telegramBotToken, { polling: true });
const oauth2Client = new OAuth2Client({
    clientId: oa_clientId,
    clientSecret: oa_clientSecret,
    redirectUri: oa_redirectUri,
});

// Create a URL for user consent
const consentUrl = oauth2Client.generateAuthUrl({
    access_type: oa_accessType,
    scope: ['https://www.googleapis.com/auth/gmail.readonly'],
});

// Redirect the user to the Google OAuth consent page
app.get('/auth', (req, res) => {

    res.redirect(consentUrl);
});

// Handle the callback with the authorization code
app.get('/callback', async (req, res) => {
    const code = req.query.code;

    try {
        const { tokens } = await oauth2Client.getToken(code);
        oauth2Client.setCredentials(tokens);

        res.send('Authentication successful. You can now monitor your Gmail account.');
        console.log("Authentication Successful")
    } catch (error) {
        console.error('Authentication error:', error);
        res.status(500).send('Authentication error. Check the console for details.');
    }
});

app.listen(port, () => {
    console.log(`App listening at http://localhost:${port}`);
});

// Set up the Gmail API
const gmail = google.gmail({
    version: 'v1',
    auth: oauth2Client,
});

// Function to check for new emails
async function checkForNewEmails() {
    try {
        const response = await gmail.users.messages.list({
            userId: 'me',
            q: 'is:unread', // Modify the query as needed
        });

        const messages = response.data.messages;

        if (messages && messages.length > 0) {
            // Perform your desired actions for new emails
            for (const message of messages) {


                const messageId = message.id;
                const email = await gmail.users.messages.get({
                    userId: 'me',
                    id: messageId,
                    format: 'full', // Get the full email content
                });

                // Send a message
                bot.sendMessage(myChatId, `New Mail \nSubject | ${email.data.subject || "No Subject"}\nBody | ${getEmailBody(email.data)}`)
                    .then(() => {
                        console.log('Message sent successfully.');
                    })
                    .catch((error) => {
                        console.error('Error sending message:', error);
                    });


            }
        } else {
            /* bot.sendMessage(myChatId, `No new mails`)
                 .then(() => {
                     console.log('Message sent successfully.');
                 })
                 .catch((error) => {
                     console.error('Error sending message:', error);
                 });
            */
            console.log('No new emails.');
        }
    } catch (error) {
        console.error('Error checking for new emails:', error);
    }
}

setInterval(checkForNewEmails, refreshtime * 60 * 1000); // 5 minutes