"""日/周/月时间范围解析（Asia/Shanghai）。"""

from __future__ import annotations

from datetime import date, datetime, timedelta
from zoneinfo import ZoneInfo

_SH = ZoneInfo("Asia/Shanghai")


def today_shanghai(now: datetime | None = None) -> str:
    n = (now or datetime.now(tz=_SH)).astimezone(_SH)
    return n.strftime("%Y-%m-%d")


def parse_ymd(ymd: str) -> date:
    return datetime.strptime(ymd, "%Y-%m-%d").date()


def day_bounds_ms(ymd: str) -> tuple[int, int]:
    """上海自然日 [start_ms, end_ms)，end 为次日 00:00。"""
    d = parse_ymd(ymd)
    start = datetime(d.year, d.month, d.day, 0, 0, 0, tzinfo=_SH)
    end = start + timedelta(days=1)
    return int(start.timestamp() * 1000), int(end.timestamp() * 1000)


def resolve_range(
    range_name: str,
    anchor_ymd: str | None = None,
    *,
    month_mode: str = "rolling_30",
    now: datetime | None = None,
) -> dict:
    """
    返回:
      anchor, start_ymd, end_ymd (含), start_ms, end_ms (半开区间), days
    """
    anchor = anchor_ymd or today_shanghai(now)
    parse_ymd(anchor)  # validate

    name = (range_name or "day").strip().lower()
    if name == "day":
        start_ymd = end_ymd = anchor
        days = 1
    elif name == "week":
        end_ymd = anchor
        start = parse_ymd(anchor) - timedelta(days=6)
        start_ymd = start.strftime("%Y-%m-%d")
        days = 7
    elif name == "month":
        end_ymd = anchor
        mode = (month_mode or "rolling_30").strip().lower()
        if mode in ("calendar", "natural", "natural_month"):
            d = parse_ymd(anchor)
            start_ymd = d.replace(day=1).strftime("%Y-%m-%d")
            days = (parse_ymd(end_ymd) - parse_ymd(start_ymd)).days + 1
        else:
            # rolling_30
            start = parse_ymd(anchor) - timedelta(days=29)
            start_ymd = start.strftime("%Y-%m-%d")
            days = 30
    else:
        raise ValueError(f"invalid range: {range_name!r}")

    start_ms, _ = day_bounds_ms(start_ymd)
    _, end_ms = day_bounds_ms(end_ymd)
    return {
        "range": name,
        "anchor": anchor,
        "start_ymd": start_ymd,
        "end_ymd": end_ymd,
        "start_ms": start_ms,
        "end_ms": end_ms,
        "days": days,
        "month_mode": month_mode if name == "month" else None,
    }