from __future__ import annotations


def normalize_email_identity(value: str | None) -> str | None:
    if value is None:
        return None
    normalized = value.strip().lower()
    return normalized or None


def mask_mobile(value: str | None) -> str | None:
    if not value:
        return None
    if len(value) <= 4:
        return value
    return f"{value[:2]}{'*' * max(len(value) - 6, 1)}{value[-4:]}"