Facebook chat bot sample on Google Cloud Functions

facebook_chatbot_GCF.js

const request = require("request");
const {Datastore} = require('@google-cloud/datastore');

const datastore = new Datastore({keyFilename: './gcpkey.json'});

const callSendAPI = (sender_id, body) => {
    let request_body = {
        recipient: {
            id: sender_id
        },
        message: body
    }

    request({
        uri: 'https://graph.facebook.com/v2.6/me/messages',
        qs: { access_token: 'SECRET_ACCESS_TOKEN' },
        method: 'POST',
        json: request_body
    }, (err, resp, body) => {
        if (err) {
            console.error('Unable to send message:' + err);
        } else {
            if (resp.statusCode === 200) {
                console.log('message sent!')
            } else {
                console.error(resp.statusCode, body)
            }
        }
    });
}

// Webhook for facebook messenger
exports.webhook = (req, res) => {
    if (req.method === 'GET') {
        const VERIFY_TOKEN = 'I don\'t say bleeh bleh bleh';

        let mode = req.query['hub.mode'];
        let token = req.query['hub.verify_token'];
        let challenge = req.query['hub.challenge'];

        if (mode && token) {
            if (mode === 'subscribe' && token === VERIFY_TOKEN) {
                console.log('WEBHOOK_VERIFIED');
                res.status(200).send(challenge);
            } else {
                res.sendStatus(403);
            }
        }
    } else if (req.method === 'POST') {
        let body = req.body;

        if (body.object === 'page') {
            body.entry.forEach((entry) => {
                let webhook_event = entry.messaging[0];

                if (webhook_event.postback) {
                    let payload = webhook_event.postback.payload;

                    if (payload === 'ping') {
                        const key = datastore.key(['reppergee', '5650385196810240']);
                        datastore.get(key).then((entity) => {
                            const balance = (entity && entity[0] && entity[0][webhook_event.sender.id]) || 0;

                            datastore.save({
                                key: key,
                                data: {
                                    [webhook_event.sender.id]: balance + 10
                                }
                            }).then(() => {
                                callSendAPI(webhook_event.sender.id, { text: `Таны дансны үлдэгдэл амжилттай 10 оноогоор нэмэгдэж, нийтдээ ${balance + 10} оноо боллоо.` });
                            }).catch(console.error);
                        });
                    }
                }
            });

            res.status(200).send('EVENT_RECEIVED');
        } else {
            res.sendStatus(404);
        }
    }
}