header.js

const { TwitterClient } = require('twitter-api-client')
const axios = require('axios')
const sharp = require('sharp')
const Feed = require('rss-to-json')
const Jimp = require('jimp')
const fs = require('fs')

const numberOfFollowers = 3
const widthHeightFollowerImage = 90

function getVariable(name) {

    if (fs.existsSync(`${__dirname}/creds.json`)) {
        return require(`${__dirname}/creds.json`)[name]
    }
    return process.env[name]
}

async function uploadBanner() {
    console.log(`Uploading to twitter...`)
    const base64 = await fs.readFileSync('/tmp/1500x500_final.png', { encoding: 'base64' });
    await twitterClient.accountsAndUsers
        .accountUpdateProfileBanner({ banner: base64 })
}

async function createBanner(headline) {
    const banner = await Jimp.read(`${__dirname}/assets/banner.png`)
    const mask = await Jimp.read(`${__dirname}/assets/mask.png`)
    const font = await Jimp.loadFont(Jimp.FONT_SANS_32_WHITE)
    // build banner
    console.log(`Adding followers...`)
    await Promise.all([...Array(numberOfFollowers)].map((_, i) => {
        return new Promise(async resolve => {
            const image = await Jimp.read(`/tmp/${i}.png`)
            const x = 600 + i * (widthHeightFollowerImage + 10);
            console.log(`Appending image ${i} with x=${x}`)
            banner.composite(image, x, 360);
            resolve()
        })
    }))
    console.log(`Adding headline...`)
    banner.print(font, 380, 250, headline);
    await banner.writeAsync('/tmp/1500x500_final.png');
}

async function getLatestArticleHeadline() {
    console.log(`Retrieving headline...`)
    const rss = await Feed.parse(`${getVariable('RSS_FEED')}`)
    const title = rss.items[0].title
    console.log(`Retrieved headline: ${title}`)
    // add padding left & right to align it properly
    const padding = ' '.repeat(Math.ceil((60 - title.length) / 2))
    return `${padding}${title}${padding}`;
}

async function saveAvatar(user, path) {
    console.log(`Retrieving avatar...`)
    const response = await axios({
        url: user.profile_image_url_https,
        responseType: 'arraybuffer'
    })
    await sharp(response.data)
        .resize(widthHeightFollowerImage, widthHeightFollowerImage)
        .toFile(path)
}

async function getImagesOfLatestFollowers() {
    console.log(`Retrieving followers...`)
    try {
        const data = await twitterClient
        .accountsAndUsers
        .followersList({
            screen_name: getVariable('TWITTER_HANDLE'),
            count: numberOfFollowers
        })
        await Promise.all(data.users
            .map((user, index) => saveAvatar(user, `/tmp/${index}.png`)))
      } catch (err) {
        console.log(err)
      }

}

const twitterClient = new TwitterClient({
    apiKey: getVariable('TWITTER_API_KEY'),
    apiSecret: getVariable('TWITTER_API_SECRET_KEY'),
    accessToken: getVariable('TWITTER_API_ACCESS_TOKEN'),
    accessTokenSecret: getVariable('TWITTER_API_ACCESS_SECRET'),
});

exports.handler = async () => {
    await getImagesOfLatestFollowers()
    const title = await getLatestArticleHeadline()
    await createBanner(title)
    await uploadBanner()
    return {
        statusCode: 200,
        body: JSON.stringify({ status: 'ok' }),
      };
}