index.js

const fs = require('fs');
const {google} = require('googleapis');
const express = require('express');

// If modifying these scopes, delete token.json.
const SCOPES = ['https://www.googleapis.com/auth/calendar.readonly'];
// The file token.json stores the user's access and refresh tokens, and is
// created automatically when the authorization flow completes for the first
// time.
const TOKEN_PATH = 'token.json';


const app = express();

// routes
app.get('/', (_, res) => {
  res.send("Welcome to the Google Calendar Events Service");
});

app.get('/get-calendar-events', function(req, res) {
  authorize(
    req.query.client_secret, 
    req.query.client_id,
    req.query.redirect_uris, 
    listEvents)
});

// spin up app on port 3000
app.listen(3000, () => {
  console.log('Server is up on port 3000');
});



function authorize(client_secret, client_id, redirect_uris, callback) {
  const oAuth2Client = new google.auth.OAuth2(
      client_id, client_secret, redirect_uris[0]);

  // Check if we have previously stored a token.
  fs.readFile(TOKEN_PATH, (err, token) => {
    if (err) return getAccessToken(oAuth2Client, callback);
    oAuth2Client.setCredentials(JSON.parse(token));
    callback(oAuth2Client);
  });
}


function getAccessToken(oAuth2Client, callback) {
  const authUrl = oAuth2Client.generateAuthUrl({
    access_type: 'offline',
    scope: SCOPES,
  });
  console.log('Authorize this app by visiting this url:', authUrl);
  const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout,
  });
  rl.question('Enter the code from that page here: ', (code) => {
    rl.close();
    oAuth2Client.getToken(code, (err, token) => {
      if (err) return console.error('Error retrieving access token', err);
      oAuth2Client.setCredentials(token);
      // Store the token to disk for later program executions
      fs.writeFile(TOKEN_PATH, JSON.stringify(token), (err) => {
        if (err) return console.error(err);
        console.log('Token stored to', TOKEN_PATH);
      });
      callback(oAuth2Client);
    });
  });
}


function listEvents(auth) {
  const calendar = google.calendar({version: 'v3', auth});
  calendar.events.list({
    calendarId: 'primary',
    timeMin: (new Date()).toISOString(),
    maxResults: 10,
    singleEvents: true,
    orderBy: 'startTime',
  }, (err, res) => {
    if (err) return console.log('The API returned an error: ' + err);
    const events = res.data.items;
    if (events.length) {
      console.log('Upcoming 10 events:');
      events.map((event, i) => {
        const start = event.start.dateTime || event.start.date;
        const end = event.end.dateTime || event.end.date;
        console.log(`start: ${start} - end: ${end} - ${event.summary}`);
      });
    } else {
      console.log('No upcoming events found.');
    }
  });
}