#!/usr/bin/env python3
# -*- coding: utf-8 -*-
from __future__ import annotations

import random
from datetime import datetime, timedelta
from typing import Iterable, Optional, Set, Tuple

from services.time_utils import BEIJING_TZ


def _parse_hhmm(value: str, default: Tuple[int, int] = (8, 0)) -> Tuple[int, int]:
    text = str(value or "").strip()
    if ":" not in text:
        return default
    try:
        h, m = text.split(":", 1)
        hour = int(h)
        minute = int(m)
        if 0 <= hour <= 23 and 0 <= minute <= 59:
            return hour, minute
    except Exception:
        pass
    return default


def _parse_weekdays(value: str, default: Iterable[int] = (1, 2, 3, 4, 5)) -> Set[int]:
    text = str(value or "").strip()
    days = []
    for part in text.split(","):
        part = part.strip()
        if not part:
            continue
        try:
            day = int(part)
        except Exception:
            continue
        if 1 <= day <= 7:
            days.append(day)
    return set(days) if days else set(default)


def _parse_cst_datetime(value: Optional[str]) -> Optional[datetime]:
    if not value:
        return None
    text = str(value).strip()
    if not text:
        return None
    try:
        naive = datetime.strptime(text, "%Y-%m-%d %H:%M:%S")
        return BEIJING_TZ.localize(naive)
    except Exception:
        return None


def compute_next_run_at(
    *,
    now: datetime,
    schedule_time: str,
    weekdays: str,
    random_delay: int = 0,
    last_run_at: Optional[str] = None,
) -> datetime:
    """
    计算下一次实际执行时间（北京时间，aware datetime）。

    规则：
    - weekday 过滤（1=周一..7=周日）
    - random_delay=1 时：在 [schedule_time-15min, schedule_time+15min] 内随机
    - 同一天只执行一次：若 last_run_at 是今天，则 next_run_at 至少是下一可用日
    """
    if now.tzinfo is None:
        now = BEIJING_TZ.localize(now)

    hour, minute = _parse_hhmm(schedule_time, default=(8, 0))
    allowed_weekdays = _parse_weekdays(weekdays, default=(1, 2, 3, 4, 5))
    random_delay = 1 if int(random_delay or 0) == 1 else 0

    last_run_dt = _parse_cst_datetime(last_run_at)
    last_run_date = last_run_dt.date() if last_run_dt else None

    base_today = now.replace(hour=hour, minute=minute, second=0, microsecond=0)
    for day_offset in range(0, 14):
        day = (base_today + timedelta(days=day_offset)).date()
        if last_run_date is not None and day == last_run_date:
            continue

        candidate_base = base_today.replace(year=day.year, month=day.month, day=day.day)
        if candidate_base.isoweekday() not in allowed_weekdays:
            continue

        if random_delay:
            window_start = candidate_base - timedelta(minutes=15)
            window_end = candidate_base + timedelta(minutes=15)

            # 只从“未来窗口”中抽样，避免抽到过去时间导致整天被跳过
            delta_seconds = (now - window_start).total_seconds()
            if delta_seconds < 0:
                min_offset = 0
            else:
                min_offset = int(delta_seconds // 60) + 1
            max_offset = int((window_end - window_start).total_seconds() // 60)
            if min_offset > max_offset:
                continue
            candidate = window_start + timedelta(minutes=random.randint(min_offset, max_offset))
        else:
            candidate = candidate_base

        if candidate <= now:
            continue
        return candidate

    # 兜底：找不到则推迟一天
    return now + timedelta(days=1)


def format_cst(dt: datetime) -> str:
    """格式化为 DB 存储用的 CST 字符串。"""
    if dt.tzinfo is None:
        dt = BEIJING_TZ.localize(dt)
    dt = dt.astimezone(BEIJING_TZ)
    return dt.strftime("%Y-%m-%d %H:%M:%S")