BitBucket PR creation webhook -> AWS Lambda -> Slack bot

lambda.js

/*
    Used for a bigger team where not everyone is on Slack. A random user from the list is chosen and notified about a PR.
    If the user is already set as a reviewer it's discarded from the random pool.
    The lambda is the most simple configuration for requests with 128MB of RAM provisioned.
    https://support.atlassian.com/bitbucket-cloud/docs/event-payloads/
    https://api.slack.com/messaging/webhooks
*/

const https = require('https');

const hook = data => new Promise((resolve, reject) => {
    const options = {
        host: 'hooks.slack.com',
        path: '/services/...', // change me
        method: 'POST',
        headers: {
            'Content-Type': 'application/json',
        },
    };

    const req = https.request(options, res => { resolve(JSON.stringify(res.statusCode)); });
    req.on('error', e => { reject(e.message); });
    req.write(JSON.stringify(data));
    req.end();
});

const users = [ // [slack_user_id, bitbucket_user_name]
    ['UDEADBEEF', 'John Smith'],
];

const pickReviewer = excludeUsers => {
    const bb_users = users.map(u => u[1]);
    const slack_users = users.map(u => u[0]);
    excludeUsers.forEach(user => {
        const i = bb_users.indexOf(user);
        if (i > -1) {
            bb_users.splice(i, 1);
            slack_users.splice(i, 1);
        }
    });

    return slack_users[Math.floor(Math.random() * slack_users.length)];
};

const bb_users = users.map(u => u[1]);
const slack_users = users.map(u => u[0]);
const getUser = user => (bb_users.indexOf(user) !== -1 ? `<@${slack_users[bb_users.indexOf(user)]}>` : user);

const reviewersList = reviewers => {
    if (reviewers.length === 0) return '';

    return `
:mag_right: ${reviewers.map(getUser).join(', ')}
`;
};

const formatSlackMessage = body => {
    const pr = body.pullrequest;

    const reviewers = pr.reviewers.map(r => r.display_name);
    const author = body.pullrequest.author.display_name;

    const text = `:git-pr: <${pr.links.html.href}|*${pr.title}*>
:writing_hand: ${pr.author.display_name}${reviewersList(reviewers)}
:game_die: <@${pickReviewer([...reviewers, author])}>`;

    return { text };
};

exports.handler = async event => {
    let body;
    let statusCode = '200';
    const headers = {
        'Content-Type': 'application/json',
        'Access-Control-Allow-Origin': '*',
    };

    try {
        if (event.httpMethod === 'POST') {
            body = await JSON.parse(event.body);

            await hook(formatSlackMessage(body))
                .then(result => console.log(`Status code: ${result}`))
                .catch(err => console.error(`Error doing the request for the event: ${JSON.stringify(event)} => ${err}`));
        }
    } catch (err) {
        statusCode = '400';
        body = err.message;
    }

    return {
        statusCode,
        body,
        headers,
    };
};