cloudflare-domain-manager/packages/shared/src/subdomain.ts

export function dnsNameToSubdomainLabel(
  recordName: string,
  zoneName: string,
): string | null {
  const rn = recordName.trim().replace(/\.+$/, "");
  const zn = zoneName.trim().replace(/\.+$/, "");
  if (!rn || !zn) return null;

  if (rn === "*") return "*";

  const wildcardFqdn = `*.${zn}`;
  if (rn.toLowerCase() === wildcardFqdn.toLowerCase()) return "*";

  if (rn.toLowerCase() === zn.toLowerCase()) return "@";

  const zoneSuffix = `.${zn}`;
  if (rn.toLowerCase().endsWith(zoneSuffix.toLowerCase())) {
    const prefix = rn.slice(0, rn.length - zoneSuffix.length);
    return prefix || "@";
  }

  if (rn.startsWith("*.")) return rn;
  if (!rn.includes(".")) return rn;

  return null;
}

export function subdomainLabelToFqdn(label: string, zoneName: string): string {
  return label === "@" ? zoneName : `${label}.${zoneName}`;
}

/** Canonical DNS record name as returned by Cloudflare for a zone. */
export function normalizeDnsRecordName(
  recordName: string,
  zoneName: string,
): string {
  const label = dnsNameToSubdomainLabel(recordName, zoneName);
  if (label == null) {
    return recordName.trim().replace(/\.+$/, "");
  }
  return subdomainLabelToFqdn(label, zoneName);
}

export function dnsRecordNamesMatch(
  left: string,
  right: string,
  zoneName: string,
): boolean {
  return (
    normalizeDnsRecordName(left, zoneName).toLowerCase() ===
    normalizeDnsRecordName(right, zoneName).toLowerCase()
  );
}