from datetime import date, datetime, timezone, timedelta

CST = timezone(timedelta(hours=8))  # China Standard Time


def today_cst() -> date:
    """Get today's date in Asia/Shanghai timezone."""
    return datetime.now(timezone.utc).astimezone(CST).date()


def parse_date(s: str) -> date:
    """Parse a date string that may be YYYY-MM-DD or a full ISO datetime."""
    return date.fromisoformat(s[:10])


def is_working_day(d: date | None = None, holidays: set[date] | None = None) -> bool:
    """Check if a date is a Chinese working day.

    Returns False for:
    - Saturdays and Sundays (weekday >= 5)
    - Dates in the holidays set (configurable via system_config)

    Note: makeup workdays (调休, where Saturday/Sunday becomes a workday)
    are not currently handled. If needed, add a 'workdays' config set.
    """
    d = d or today_cst()
    if d.weekday() >= 5:  # Saturday or Sunday
        return False
    if holidays and d in holidays:
        return False
    return True