def mask_str(value: str) -> str:
    """Mask a word."""
    if len(value) < 2:
        return "*"
    return f"{value[0]}{'*' * (len(value) - 1)}"


def mask_email(email: str) -> str:
    """Mask an email address."""
    if "@" not in email:
        return mask_str(email)
    local, domain = email.split("@")
    parts = local.split(".")
    domain_name, domain_tld = domain.split(".", maxsplit=1)
    return f"{'.'.join(map(mask_str, parts))}@{mask_str(domain_name)}.{domain_tld}"


def mask_phone_number(phone_number: str) -> str:
    """Mask a phone number."""
    return "*" * len(phone_number)