from datetime import datetime
from zoneinfo import ZoneInfo

_tz = ZoneInfo("Asia/Taipei")


def configure_timezone(tz_name: str) -> None:
    """Update the application timezone. Called on startup and when settings change."""
    global _tz
    try:
        _tz = ZoneInfo(tz_name)
    except Exception:
        _tz = ZoneInfo("Asia/Taipei")


def now_tw() -> datetime:
    """Return current time in the configured timezone as a naive datetime."""
    return datetime.now(tz=_tz).replace(tzinfo=None)