offscreen.js

chrome.runtime.onMessage.addListener(async (request) => {
  if (request.action === 'createPdfOffscreen') {
    const { imageUrls, mangaTitle, chapter } = request;
    const { jsPDF } = window.jspdf;
    const pdf = new jsPDF();

    for (let i = 0; i < imageUrls.length; i++) {
      const dataUrl = imageUrls[i];
      await new Promise(resolve => {
        const img = new Image();
        img.src = dataUrl;
        img.onload = function () {
          const pageWidth = pdf.internal.pageSize.getWidth();
          const pageHeight = pdf.internal.pageSize.getHeight();
          const ratio = Math.min(pageWidth / img.width, pageHeight / img.height);
          const imgWidth = img.width * ratio;
          const imgHeight = img.height * ratio;
          const x = (pageWidth - imgWidth) / 2;
          const y = (pageHeight - imgHeight) / 2;
          if (i > 0) {
            pdf.addPage();
          }
          // The format (e.g., 'PNG', 'JPEG') is part of the data URL, but jsPDF can handle it.
          pdf.addImage(img, 'PNG', x, y, imgWidth, imgHeight);
          resolve();
        }
        img.onerror = () => resolve(); // Continue if an image fails to load
      });
    }

    const pdfBlob = pdf.output('blob');
    const pdfFilename = `${mangaTitle} - ${chapter.name}.pdf`;

    const reader = new FileReader();
    reader.onload = function () {
      // Send the data URL back to the service worker to handle the download
      chrome.runtime.sendMessage({
        action: 'downloadPdf',
        url: reader.result,
        filename: pdfFilename
      });
    };
    reader.readAsDataURL(pdfBlob);
  }
});