const crypto = require('crypto');
const fs = require('fs');

// Function to create HMAC for a file using streams
function createHmacForFile(filePath, algorithm, key) {
  return new Promise((resolve, reject) => {
    // Create Hmac object
    const hmac = crypto.createHmac(algorithm, key);
    
    // Create read stream
    const stream = fs.createReadStream(filePath);
    
    // Handle stream events
    stream.on('data', (data) => {
      hmac.update(data);
    });
    
    stream.on('end', () => {
      const digest = hmac.digest('hex');
      resolve(digest);
    });
    
    stream.on('error', (error) => {
      reject(error);
    });
  });
}

// Secret key
const secretKey = 'file-authentication-key';

// Example usage (adjust file path as needed)
const filePath = 'example.txt';

// Create a test file if it doesn't exist
if (!fs.existsSync(filePath)) {
  fs.writeFileSync(filePath, 'This is a test file for HMAC authentication.\n'.repeat(100));
  console.log(`Created test file: ${filePath}`);
}

// Create HMAC for the file with different algorithms
Promise.all([
  createHmacForFile(filePath, 'md5', secretKey),
  createHmacForFile(filePath, 'sha1', secretKey),
  createHmacForFile(filePath, 'sha256', secretKey)
])
.then(([md5Digest, sha1Digest, sha256Digest]) => {
  console.log(`File: ${filePath}`);
  console.log(`Secret Key: ${secretKey}`);
  console.log(`HMAC-MD5: ${md5Digest}`);
  console.log(`HMAC-SHA1: ${sha1Digest}`);
  console.log(`HMAC-SHA256: ${sha256Digest}`);
  
  // Store the HMAC for later verification
  fs.writeFileSync(`${filePath}.hmac`, sha256Digest);
  console.log(`HMAC stored in: ${filePath}.hmac`);
})
.catch(error => {
  console.error('Error creating HMAC for file:', error.message);
});