from __future__ import annotations

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


DEFAULT_TIMEZONE = "Asia/Shanghai"
DATETIME_DISPLAY_FORMAT = "%Y-%m-%d %H:%M:%S"


def utc_now() -> datetime:
    return datetime.now(timezone.utc).replace(tzinfo=None)


def current_year_for_timezone(timezone_name: str | None) -> int:
    return datetime.now(timezone.utc).astimezone(timezone_for_name(timezone_name)).year


def timezone_for_name(name: str | None) -> ZoneInfo:
    try:
        return ZoneInfo((name or DEFAULT_TIMEZONE).strip() or DEFAULT_TIMEZONE)
    except ZoneInfoNotFoundError:
        return ZoneInfo(DEFAULT_TIMEZONE)


def format_datetime_for_timezone(value: datetime | None, timezone_name: str | None) -> str:
    if value is None:
        return "-"
    if value.tzinfo is None:
        value = value.replace(tzinfo=timezone.utc)
    return value.astimezone(timezone_for_name(timezone_name)).strftime(DATETIME_DISPLAY_FORMAT)