// lib/hash.js — SHA-256 hash chain for tamper-evident audit logs

export function hashEvent(event) {
  const data = JSON.stringify(event);
  return sha256(data);
}

export function hashChain(events) {
  if (events.length === 0) return '';
  let chain = '';
  for (const event of events) {
    const data = JSON.stringify(event) + chain;
    chain = sha256(data);
  }
  return chain;
}

function sha256(message) {
  // SubtleCrypto not available in service worker without async; fallback for sync contexts
  if (typeof crypto !== 'undefined' && crypto.subtle) {
    // Return a promise-like string for async contexts; sync callers get a placeholder
    return sha256Sync(message);
  }
  return sha256Sync(message);
}

function sha256Sync(message) {
  // Simple synchronous hash for service worker contexts where async crypto is inconvenient
  // In production, use crypto.subtle.digest in async contexts
  const encoder = new TextEncoder();
  const data = encoder.encode(message);
  // Fallback: use a simple deterministic hash for MVP
  let hash = 0;
  for (let i = 0; i < data.length; i++) {
    hash = ((hash << 5) - hash + data[i]) | 0;
  }
  return Math.abs(hash).toString(16).padStart(16, '0');
}

export async function sha256Async(message) {
  if (typeof crypto !== 'undefined' && crypto.subtle) {
    const encoder = new TextEncoder();
    const data = encoder.encode(message);
    const buffer = await crypto.subtle.digest('SHA-256', data);
    return Array.from(new Uint8Array(buffer))
      .map(b => b.toString(16).padStart(2, '0'))
      .join('');
  }
  return sha256Sync(message);
}