"""Reserved localparts that may not be registered (SPEC §4/§6.1).

Mail-grade from day one: role addresses (RFC 2142) plus common admin/system
handles. Comparison is case-insensitive; keep entries lowercase.
"""

from __future__ import annotations

RESERVED_LOCALPARTS: frozenset[str] = frozenset(
    {
        # RFC 2142 role addresses
        "postmaster",
        "abuse",
        "hostmaster",
        "webmaster",
        "usenet",
        "news",
        "www",
        "uucp",
        "ftp",
        "noc",
        "security",
        "mailer-daemon",
        # Common system/admin handles
        "admin",
        "administrator",
        "root",
        "noreply",
        "no-reply",
        "donotreply",
        "do-not-reply",
        "support",
        "help",
        "info",
        "contact",
        "sales",
        "billing",
        "system",
        "daemon",
        "nobody",
        "null",
        "void",
        "test",
    }
)


def is_reserved(localpart: str) -> bool:
    """Return True if ``localpart`` is reserved (case-insensitive)."""
    return localpart.lower() in RESERVED_LOCALPARTS