<script src="https://cdnjs.cloudflare.com/ajax/libs/pdf.js/2.16.105/pdf.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jspdf/2.5.1/jspdf.umd.min.js"></script>
<script src="https://unpkg.com/pdf-lib/dist/pdf-lib.min.js"></script>

<input type="file" id="upload" accept=".pdf" />
<button onclick="compressPDF()">Compress & Download</button>

<script>
  async function compressPDF() {
    const file = document.getElementById('upload').files[0];
    if (!file) return alert("Please select a PDF!");

    // 1. Load the PDF using pdf.js
    const arrayBuffer = await file.arrayBuffer();
    const pdf = await pdfjsLib.getDocument(arrayBuffer).promise;
    
    // Initialize jsPDF (The builder)
    const { jsPDF } = window.jspdf;
    const newPdf = new jsPDF();

    // 2. Loop through every page
    for (let i = 1; i <= pdf.numPages; i++) {
      const page = await pdf.getPage(i);
      
      // Determine scale (lower scale = smaller file but blurrier)
      const viewport = page.getViewport({ scale: 1 }); 
      
      // Create a temporary canvas to render the page
      const canvas = document.createElement('canvas');
      const ctx = canvas.getContext('2d');
      canvas.width = viewport.width;
      canvas.height = viewport.height;

      // Render page to canvas
      await page.render({ canvasContext: ctx, viewport: viewport }).promise;

      // 3. Compress: Convert canvas to JPEG with 0.5 quality (50%)
      const imgData = canvas.toDataURL('image/jpeg', 0.5); 

      // 4. Add image to the new PDF
      if (i > 1) newPdf.addPage();
      const pdfWidth = newPdf.internal.pageSize.getWidth();
      const pdfHeight = newPdf.internal.pageSize.getHeight();
      newPdf.addImage(imgData, 'JPEG', 0, 0, pdfWidth, pdfHeight);
    }

    // 5. Save
    newPdf.save("compressed.pdf");
  }

  async function mergePDFs(file1, file2) {
    const { PDFDocument } = PDFLib;

    // 1. Load both documents
    const pdf1Bytes = await file1.arrayBuffer();
    const pdf2Bytes = await file2.arrayBuffer();

    const pdf1 = await PDFDocument.load(pdf1Bytes);
    const pdf2 = await PDFDocument.load(pdf2Bytes);

    // 2. Copy all pages from PDF 2
    const copiedPages = await pdf1.copyPages(pdf2, pdf2.getPageIndices());

    // 3. Add them to PDF 1
    copiedPages.forEach((page) => pdf1.addPage(page));

    // 4. Save
    const mergedPdfBytes = await pdf1.save();
    
    // (Helper function to trigger download would go here)
    downloadBlob(mergedPdfBytes, "merged.pdf");
  }
</script>