index.ts

import * as functions from "firebase-functions";
import * as admin from "firebase-admin";
import * as fs from "fs";
import * as path from 'path';

const app = admin.initializeApp();
const firestore = admin.firestore(app);

exports.post = functions.https.onRequest(async (req, res) => {
    // Get post ID from url params
    const params = req.url.split('/');
    const postID = params[params.length - 1].trim();
    if (!postID) {
        res.status(404).send('Post not found.');
    }

    // Get the post snapshot from Firestore
    const postSnapshot = await firestore.doc(`posts/${postID}`).get();

    // Check if the post exists
    if (!postSnapshot.exists) {
        res.status(404).send('Post not found.');
        return;
    }

    // Extract the data from the post
    const postData = postSnapshot.data()!;

    const operations = [{
        // Pass image from Cloud Storage
        operation: 'input',
        type: 'gcs',
        source: postData.imagePath
    },
    {
        // Resize to the common thumbnail size
        operation: 'resize',
        width: '1200',
        height: '630',
        fit: 'cover'
    },
    {
        // Add title text
        operation: 'text',
        value: postData.title.toUpperCase(),
        font: '900 70px sans-serif',
        strokeWidth: 1,
        maxWidth: 1000,
        wrap: true,
        left: 50,
        top: 450,
    },
    {
        // Add subtitle text
        operation: 'text',
        value: postData.subtitle,
        font: '400 40px sans-serif',
        maxWidth: 1000,
        textColor: '#ffffffcc',
        wrap: true,
        left: 50,
        top: 520,
    },
    {
        // Output as JPG, reduce quality
        operation: 'output',
        quality: 80,
        format: 'jpeg'
    },
    ];

    // Encode query parameters from operations and pass it to the Cloud Function
    const encodedOperations = encodeURIComponent(JSON.stringify(operations));
    return `https://{FUNCTIONS_REGION}-{PROJECT_ID}.cloudfunctions.net/ext-image-processing-api-handler/process?operations=${encodedOperations}`;

    // Return HTML file with metadata variables
    const templatePath = path.join(__dirname, './assets/html/post.html');
    var source = fs.readFileSync(templatePath, { encoding: 'utf-8' })
        .replaceAll('{{title}}', postData.title)
        .replaceAll('{{subtitle}}', postData.subtitle)
        .replaceAll('{{imageUrl}}', imageUrl);

    res.status(200).send(source);
});