Hash an email

import { createHash } from 'node:crypto';

const PLUS_ADDRESSING_DOMAINS = new Set([
  'gmail.com',
  'outlook.com',
  'hotmail.com',
  'live.com',
  'msn.com',
  'icloud.com',
  'me.com',
  'mac.com',
  'proton.me',
  'protonmail.com',
  'pm.me',
  'fastmail.com',
  'fastmail.fm',
]);

export function normaliseEmail(raw) {
  const value = raw.trim().normalize('NFKC').toLowerCase();
  const at = value.lastIndexOf('@');
  if (at <= 0 || at === value.length - 1 || /\s/.test(value)) return null;

  let local = value.slice(0, at);
  let domain = value.slice(at + 1);
  if (domain.endsWith('.')) domain = domain.slice(0, -1);
  if (!domain) return null;
  if (domain === 'googlemail.com') domain = 'gmail.com';

  if (PLUS_ADDRESSING_DOMAINS.has(domain)) {
    const plus = local.indexOf('+');
    if (plus >= 0) local = local.slice(0, plus);
  }
  if (domain === 'gmail.com') local = local.replaceAll('.', '');
  return local ? `${local}@${domain}` : null;
}

export function registryDigest(email) {
  const normalised = normaliseEmail(email);
  return normalised && createHash('sha256').update(normalised).digest('hex');
}

const digest = registryDigest(signupEmail);
if (digest === null) {
  // Not an email address. Skip the registry for this value.
}