interface IdTokenClaims {
  email?: unknown;
}

export function getEmailFromIdToken(idToken: string | undefined): string | undefined {
  if (!idToken) return undefined;

  try {
    const payload = idToken.split('.')[1];
    if (!payload) return undefined;

    const claims = JSON.parse(Buffer.from(payload, 'base64url').toString('utf8')) as IdTokenClaims;
    return typeof claims.email === 'string' && claims.email.length > 0 ? claims.email : undefined;
  } catch {
    return undefined;
  }
}