Client-side Hash (SHA-256)

async function generateFileHash(file: File): Promise<string> {
  const arrayBuffer = await file.arrayBuffer();
  const hashBuffer = await crypto.subtle.digest('SHA-256', arrayBuffer);
  
  // Convert to hex string
  const hashArray = Array.from(new Uint8Array(hashBuffer));
  const hashHex = hashArray.map(b => b.toString(16).padStart(2, '0')).join('');
  
  return hashHex;
}

// With progress tracking for large files
async function generateHashWithProgress(
  file: File,
  onProgress: (percent: number) => void
): Promise<string> {
  const chunkSize = 2 * 1024 * 1024; // 2MB chunks
  const chunks: Uint8Array[] = [];
  let loaded = 0;
  
  // Read file in chunks to show progress
  for (let start = 0; start < file.size; start += chunkSize) {
    const chunk = file.slice(start, start + chunkSize);
    const buffer = await chunk.arrayBuffer();
    chunks.push(new Uint8Array(buffer));
    
    loaded += buffer.byteLength;
    onProgress((loaded / file.size) * 100);
  }
  
  // Combine and hash
  const totalLength = chunks.reduce((sum, c) => sum + c.length, 0);
  const combined = new Uint8Array(totalLength);
  let offset = 0;
  
  for (const chunk of chunks) {
    combined.set(chunk, offset);
    offset += chunk.length;
  }
  
  const hashBuffer = await crypto.subtle.digest('SHA-256', combined);
  const hashArray = Array.from(new Uint8Array(hashBuffer));
  return hashArray.map(b => b.toString(16).padStart(2, '0')).join('');
}

// Deduplication example
const hashCache = new Map<string, boolean>();

async function uploadWithDeduplication(file: File): Promise<void> {
  const hash = await generateFileHash(file);
  
  if (hashCache.has(hash)) {
    console.log('File already uploaded, skipping...');
    return;
  }
  
  // Check server-side
  const checkResponse = await fetch(`/api/files/check/${hash}`);
  const { exists } = await checkResponse.json();
  
  if (exists) {
    console.log('File exists on server, skipping upload');
    hashCache.set(hash, true);
    return;
  }
  
  // Upload
  const formData = new FormData();
  formData.append('file', file);
  formData.append('hash', hash);
  
  await fetch('/api/upload', { method: 'POST', body: formData });
  hashCache.set(hash, true);
}