import { createHmac, timingSafeEqual } from 'node:crypto';

export function verifyWebhook(rawBody, signature, secrets, now = Date.now()) {
  if (!Buffer.isBuffer(rawBody) || rawBody.length > 65536) throw new Error('Invalid body.');
  const match = /^t=(\d{1,12}),v1=([a-f0-9]{64})$/.exec(signature || '');
  if (!match || Math.abs(now / 1000 - Number(match[1])) > 300) {
    throw new Error('Invalid or expired signature.');
  }
  const provided = Buffer.from(match[2], 'hex');
  const keys = Array.isArray(secrets) ? secrets : [secrets];
  const valid = keys.filter(key => typeof key === 'string' && key.startsWith('whsec_')).some(key => {
    const expected = createHmac('sha256', key)
      .update(match[1] + '.').update(rawBody).digest();
    return timingSafeEqual(provided, expected);
  });
  if (!valid) throw new Error('Invalid signature.');
  const event = JSON.parse(rawBody.toString('utf8'));
  const statuses = ['verified', 'expired', 'cancelled'];
  if (!event || typeof event.id !== 'string' || !event.id.startsWith('evt_') ||
      !event.data || !statuses.includes(event.data.status) ||
      event.type !== 'verification.' + event.data.status) {
    throw new Error('Invalid event.');
  }
  // The receiver must still compare Veri-Event-ID to event.id, bind event.data
  // to its stored attempt, check live/mode/state/reference, and deduplicate in DB.
  return event;
}