from __future__ import annotations

from datetime import UTC, datetime, timedelta, timezone
from zoneinfo import ZoneInfo, ZoneInfoNotFoundError


def resolve_timezone(timezone_name: str):
    try:
        return ZoneInfo(timezone_name)
    except ZoneInfoNotFoundError:
        fallback_mapping = {
            "Asia/Shanghai": timezone(timedelta(hours=8)),
            "Asia/Hong_Kong": timezone(timedelta(hours=8)),
            "UTC": UTC,
        }
        return fallback_mapping.get(timezone_name, UTC)


def format_now(timezone_name: str) -> str:
    current = datetime.now(resolve_timezone(timezone_name))
    return current.strftime("%Y-%m-%d %H:%M:%S.%f")[:-3]