import { createHmac, timingSafeEqual } from 'crypto';

const SECRET =
  process.env.UNSUBSCRIBE_SECRET ||
  process.env.COOKIE_SECRET ||
  process.env.SECRET ||
  'default-secret-change-in-production';

export function generateUnsubscribeToken(email: string, category: string): string {
  const data = `${email}:${category}`;
  return createHmac('sha256', SECRET).update(data).digest('hex');
}

export function verifyUnsubscribeToken(
  email: string,
  category: string,
  token: string,
): boolean {
  const expectedToken = generateUnsubscribeToken(email, category);
  const tokenBuffer = Buffer.from(token, 'hex');
  const expectedBuffer = Buffer.from(expectedToken, 'hex');

  // Handle length mismatch safely to avoid timing leaks
  if (tokenBuffer.length !== expectedBuffer.length) {
    // Compare against zero-filled buffer of same length as token to maintain constant time
    const zeroBuffer = Buffer.alloc(tokenBuffer.length);
    timingSafeEqual(tokenBuffer, zeroBuffer);
    return false;
  }

  return timingSafeEqual(tokenBuffer, expectedBuffer);
}

export function getUnsubscribeUrl(email: string, category: string): string {
  const token = generateUnsubscribeToken(email, category);
  const params = new URLSearchParams({ email, category, token });
  const dashboardUrl = process.env.DASHBOARD_URL || 'http://localhost:3000';
  return `${dashboardUrl}/unsubscribe?${params.toString()}`;
}