"""Asia/Shanghai 日切与时段桶。时间戳一律 UTC ms 入，上海出。"""

from __future__ import annotations

from datetime import datetime, timedelta
from zoneinfo import ZoneInfo

_SH = ZoneInfo("Asia/Shanghai")


def _to_shanghai(ts_ms: int) -> datetime:
    return datetime.fromtimestamp(int(ts_ms) / 1000.0, tz=_SH)


def shanghai_day(ts_ms: int) -> str:
    """上海自然日 YYYY-MM-DD。"""
    return _to_shanghai(ts_ms).strftime("%Y-%m-%d")


def shanghai_bucket(ts_ms: int, bucket_minutes: int = 60) -> int:
    """
    日内时段桶起点（分钟，0–1439）。
    默认 60 → 0,60,120,...,1380（即小时 0–23）。
    """
    if bucket_minutes <= 0:
        raise ValueError("bucket_minutes must be > 0")
    dt = _to_shanghai(ts_ms)
    minutes = dt.hour * 60 + dt.minute
    return (minutes // bucket_minutes) * bucket_minutes


def shanghai_bucket_hour(ts_ms: int) -> int:
    """0–23 小时桶。"""
    return shanghai_bucket(ts_ms, 60) // 60


def rolling_day_start(anchor_ymd: str, days: int) -> str:
    """锚点日（含）往前 days-1 天的起始 YYYY-MM-DD。"""
    d = datetime.strptime(anchor_ymd, "%Y-%m-%d").date()
    start = d - timedelta(days=max(0, days - 1))
    return start.strftime("%Y-%m-%d")