Cloudflare worker that returns a book cover given a book title and author name using the Open Library API

worker.js

addEventListener('fetch', event => {
  event.respondWith(handleRequest(event.request))
})

const DEFAULT_IMAGE_URL = '';  // Update to your own default image

async function handleRequest(request) {
  const url = new URL(request.url);
  const bookTitle = url.searchParams.get('book_title') || '';
  const authorName = url.searchParams.get('author_name') || '';

  // Attempt to fetch ISBNs from Open Library
  const isbns = await fetchISBNs(bookTitle, authorName);
  if (isbns.length === 0) {
    console.log("No ISBNs found, using default image.");
    return fetchAndCacheImage(DEFAULT_IMAGE_URL);
  }

  // Try fetching cover images for the first ten ISBNs
  for (let i = 0; i < Math.min(10, isbns.length); i++) {
    const coverUrl = `https://covers.openlibrary.org/b/isbn/${isbns[i]}-L.jpg?default=false`;
    const imageResponse = await fetch(coverUrl);
    if (imageResponse.ok) {
      console.log(`Cover image found for ISBN ${isbns[i]}`);
      return new Response(imageResponse.body, {
        headers: {
          'Content-Type': 'image/jpeg'
        }
      });
    } else {
      console.log(`No cover found for ISBN ${isbns[i]}`);
    }
  }

  // If no valid cover images were found, return the default image
  console.log("No valid covers found, using default image.");
  return fetchAndCacheImage(DEFAULT_IMAGE_URL);
}

async function fetchISBNs(bookTitle, authorName) {
  const searchUrl = `https://openlibrary.org/search.json?title=${encodeURIComponent(bookTitle)}&author=${encodeURIComponent(authorName)}&fields=isbn`;
  const response = await fetch(searchUrl);
  if (!response.ok) {
    console.error("Failed to fetch ISBNs:", response.statusText);
    return [];
  }

  const data = await response.json();
  if (data.docs.length > 0 && data.docs[0].isbn) {
    return data.docs[0].isbn;
  }
  return [];
}

async function fetchAndCacheImage(imageUrl) {
  console.log(`Fetching image from URL: ${imageUrl}`);
  const imageResponse = await fetch(imageUrl);
  return new Response(imageResponse.body, {
    status: imageResponse.status,
    statusText: imageResponse.statusText,
    headers: {
      'Cache-Control': 'public, max-age=31536000, immutable', // Cache for 1 year
      'Content-Type': 'image/jpeg'
    }
  });
}