"""国内期货交易时段与盘前连接窗口。"""
from __future__ import annotations

from datetime import datetime, timedelta
from typing import Optional
from zoneinfo import ZoneInfo

TZ = ZoneInfo("Asia/Shanghai")

# 各交易段开盘时刻 (时, 分)
SESSION_OPENS = (
    (9, 0),
    (13, 30),
    (21, 0),
)


def is_trading_session(now: Optional[datetime] = None) -> bool:
    d = now or datetime.now(TZ)
    if d.tzinfo is None:
        d = d.replace(tzinfo=TZ)
    else:
        d = d.astimezone(TZ)
    wd = d.weekday()
    if wd == 6:
        return False
    if wd == 5 and d.hour < 21:
        return False
    t = d.hour * 60 + d.minute
    def in_range(sh: int, sm: int, eh: int, em: int) -> bool:
        return t >= sh * 60 + sm and t < eh * 60 + em
    if in_range(9, 0, 11, 30):
        return True
    if in_range(13, 30, 15, 0):
        return True
    if in_range(21, 0, 24, 0):
        return True
    if in_range(0, 0, 2, 30):
        return True
    return False


def _session_open_allowed(day: datetime, hour: int, minute: int) -> bool:
    wd = day.weekday()
    if (hour, minute) == (9, 0) or (hour, minute) == (13, 30):
        return wd < 5
    if (hour, minute) == (21, 0):
        if wd < 5:
            return True
        return wd == 5
    return False


def iter_session_starts(
    start: datetime,
    *,
    hours_ahead: int = 36,
) -> list[datetime]:
    """列出 start 之后若干小时内的各段开盘时刻。"""
    if start.tzinfo is None:
        start = start.replace(tzinfo=TZ)
    else:
        start = start.astimezone(TZ)
    end = start + timedelta(hours=hours_ahead)
    out: list[datetime] = []
    day = start.replace(hour=0, minute=0, second=0, microsecond=0)
    while day <= end:
        for h, m in SESSION_OPENS:
            if not _session_open_allowed(day, h, m):
                continue
            dt = day.replace(hour=h, minute=m)
            if dt > start and dt <= end:
                out.append(dt)
        day += timedelta(days=1)
    out.sort()
    return out


def minutes_until_next_session(now: Optional[datetime] = None) -> Optional[float]:
    d = now or datetime.now(TZ)
    if d.tzinfo is None:
        d = d.replace(tzinfo=TZ)
    else:
        d = d.astimezone(TZ)
    starts = iter_session_starts(d, hours_ahead=48)
    if not starts:
        return None
    return (starts[0] - d).total_seconds() / 60.0


def in_premarket_connect_window(
    now: Optional[datetime] = None,
    *,
    minutes_before: int = 30,
) -> bool:
    """距下一段开盘 <= minutes_before 分钟，且当前尚未进入交易时段。"""
    if is_trading_session(now):
        return False
    mins = minutes_until_next_session(now)
    if mins is None:
        return False
    return 0 < mins <= float(minutes_before)