"""合约选择：次日 16:00（上海）到期 + ATM 行权价（暂定默认，待拍板可改）。"""

from __future__ import annotations

import re
from datetime import datetime, timedelta, timezone
from typing import Any
from zoneinfo import ZoneInfo

from .types import OptionPair

_SH = ZoneInfo("Asia/Shanghai")
_DATE_RE = re.compile(r"^\d{6}$")


def safe_float(v: Any) -> float | None:
    if v is None or v == "":
        return None
    try:
        return float(v)
    except (TypeError, ValueError):
        return None


def parse_option_inst_id(inst_id: str) -> tuple[str | None, float | None, str | None]:
    """ETH-USD_UM-YYMMDD-STRIKE-C → (YYMMDD, strike, C|P)."""
    parts = (inst_id or "").strip().split("-")
    if len(parts) < 5:
        return None, None, None
    ymd = parts[-3]
    strike = safe_float(parts[-2])
    opt = parts[-1].upper()
    if not _DATE_RE.fullmatch(ymd) or strike is None or opt not in ("C", "P"):
        return None, None, None
    return ymd, strike, opt


def expiry_ms_from_ymd(ymd: str) -> int:
    """OKX 期权到期：当日 08:00 UTC = 上海 16:00。"""
    yy, mm, dd = int(ymd[0:2]), int(ymd[2:4]), int(ymd[4:6])
    dt = datetime(2000 + yy, mm, dd, 8, 0, 0, tzinfo=timezone.utc)
    return int(dt.timestamp() * 1000)


def next_session_expiry_ymd(now: datetime | None = None) -> str:
    """
    业务约定：开仓选「次日 16:00」到期。
    - 上海时间 >= 当日 16:00：目标到期日 = 次日
    - 上海时间 < 当日 16:00：目标到期日 = 当日（当日 16:00 到期仍可用作盘口对齐/预热）
    正式开仓窗从当日 16:00 起，届时「次日」即日历次日。
    """
    now_sh = (now or datetime.now(tz=_SH)).astimezone(_SH)
    open_today = now_sh.replace(hour=16, minute=0, second=0, microsecond=0)
    if now_sh >= open_today:
        target = now_sh.date() + timedelta(days=1)
    else:
        target = now_sh.date()
    return target.strftime("%y%m%d")


def pick_atm_strike(strikes: list[float], mark_px: float) -> float | None:
    if not strikes or mark_px <= 0:
        return None
    return min(strikes, key=lambda s: (abs(s - mark_px), s))


def select_option_pair(
    instruments: list[dict[str, Any]],
    *,
    mark_px: float,
    expiry_ymd: str | None = None,
    now: datetime | None = None,
) -> OptionPair | None:
    """
    从 live 合约列表中选出：目标到期日 + ATM 同行权价 Call/Put。
    行权价规则暂定 ATM（最接近标记/指数价）；待拍板后可替换。
    """
    ymd = expiry_ymd or next_session_expiry_ymd(now)
    by_strike: dict[float, dict[str, str]] = {}

    for row in instruments:
        if not isinstance(row, dict):
            continue
        state = str(row.get("state") or "live").lower()
        if state and state != "live":
            continue

        inst_id = str(row.get("instId") or "")
        y, stk, opt = parse_option_inst_id(inst_id)

        if y is None or stk is None or opt is None:
            exp = safe_float(row.get("expTime"))
            if exp:
                ms = int(exp) if exp > 10_000_000_000 else int(exp * 1000)
                y = datetime.fromtimestamp(ms / 1000, tz=timezone.utc).strftime("%y%m%d")
            stk = safe_float(row.get("stk"))
            opt_raw = str(row.get("optType") or "").upper()
            opt = opt_raw if opt_raw in ("C", "P") else None

        if not inst_id or y != ymd or stk is None or opt not in ("C", "P"):
            continue
        by_strike.setdefault(float(stk), {})[opt] = inst_id

    complete = {s: v for s, v in by_strike.items() if "C" in v and "P" in v}
    if not complete:
        return None

    atm = pick_atm_strike(list(complete.keys()), mark_px)
    if atm is None:
        return None

    legs = complete[atm]
    return OptionPair(
        expiry_ymd=ymd,
        expiry_ms=expiry_ms_from_ymd(ymd),
        strike=atm,
        call_inst_id=legs["C"],
        put_inst_id=legs["P"],
    )