Backend Implementation

const express = require('express');
const multer = require('multer');
const upload = multer();

app.post('/api/sign', upload.single('document'), async (req, res) => {
  try {
    const { eventId, auditTrail, documentFields, signerFields } = req.body;
    const document = req.file.buffer.toString('base64');
    
    // 1. Fill document fields
    const annotated = await fetch('https://api.superdoc.dev/v1/annotate', {
      method: 'POST',
      headers: { 
        'Authorization': `Bearer ${process.env.SUPERDOC_API_KEY}`,
        'Content-Type': 'application/json'
      },
      body: JSON.stringify({
        document,
        fields: [...documentFields, ...signerFields]
      })
    });
    
    if (!annotated.ok) throw new Error('Annotation failed');
    
    // 2. Apply digital signature
    const annotatedBlob = await annotated.blob();
    const signed = await fetch('https://api.superdoc.dev/v1/sign', {
      method: 'POST',
      headers: { 
        'Authorization': `Bearer ${process.env.SUPERDOC_API_KEY}`,
        'Content-Type': 'application/json'
      },
      body: JSON.stringify({
        document: Buffer.from(await annotatedBlob.arrayBuffer()).toString('base64'),
        auditTrail
      })
    });
    
    if (!signed.ok) throw new Error('Signing failed');
    
    // 3. Save signed PDF
    const signedPdf = await signed.blob();
    await saveToS3(signedPdf, `signed/${eventId}.pdf`);
    
    // 4. Log for compliance
    await db.signatures.create({
      eventId,
      signerName: signerFields.find(f => f.id === 'signature')?.value,
      signedAt: new Date(),
      auditTrail: JSON.stringify(auditTrail)
    });
    
    res.json({ success: true, documentId: eventId });
    
  } catch (error) {
    console.error('Signing failed:', error);
    res.status(500).json({ error: 'Failed to sign document' });
  }
});

app.post('/api/generate-pdf', async (req, res) => {
  const { documentSource, fileName } = req.body;
  
  // If documentSource is URL, fetch it
  let document;
  if (typeof documentSource === 'string' && documentSource.startsWith('http')) {
    const docResponse = await fetch(documentSource);
    document = Buffer.from(await docResponse.arrayBuffer()).toString('base64');
  } else {
    document = documentSource; // Already base64 or will be handled
  }
  
  // 1. Convert to PDF
  const result = await fetch('https://api.superdoc.dev/v1/convert?from=docx&to=pdf', {
    method: 'POST',
    headers: { 
      'Authorization': `Bearer ${process.env.SUPERDOC_API_KEY}`,
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({
      document,
    })
  });
  
  if (!result.ok) throw new Error('PDF generation failed');
  
  // Send PDF back to frontend
  const pdf = await result.blob();
  res.type('application/pdf');
  res.send(Buffer.from(await pdf.arrayBuffer()));
});