from datetime import datetime, timedelta
from zoneinfo import ZoneInfo

TZ = ZoneInfo("Asia/Shanghai")
DAY_CUTOFF_HOUR = 8


def now_shanghai() -> datetime:
    return datetime.now(TZ)


def _align_cutoff(dt: datetime) -> datetime:
    cutoff = dt.replace(hour=DAY_CUTOFF_HOUR, minute=0, second=0, microsecond=0)
    if dt < cutoff:
        cutoff -= timedelta(days=1)
    return cutoff


def get_yesterday_period(now: datetime | None = None) -> tuple[datetime, datetime]:
    """[D-1 08:00, D 08:00) in Shanghai time."""
    now = now or now_shanghai()
    end = _align_cutoff(now)
    start = end - timedelta(days=1)
    return start, end


def get_daybefore_period(now: datetime | None = None) -> tuple[datetime, datetime]:
    """前日周期 [D-2 08:00, D-1 08:00) in Shanghai time."""
    now = now or now_shanghai()
    end = _align_cutoff(now) - timedelta(days=1)
    start = end - timedelta(days=1)
    return start, end


def get_today_period(now: datetime | None = None) -> tuple[datetime, datetime]:
    """[D 08:00, now) in Shanghai time."""
    now = now or now_shanghai()
    start = _align_cutoff(now)
    return start, now


def to_ms(dt: datetime) -> int:
    return int(dt.timestamp() * 1000)