from __future__ import annotations

import re
from datetime import datetime
from typing import Optional

from module.logger import logger


DOWNTIME_FORMAT_RE = re.compile(
    r'(\d{4})-(\d{1,2})-(\d{1,2}) '
    r'(\d{1,2}):(\d{2})~(\d{1,2}):(\d{2})',
)

def parse_downtime(downtime: str) -> Optional[datetime]:
    """
    Parse downtime window string into end datetime.

    Args:
        downtime (str): Window string in format 'YYYY-MM-DD HH:MM~HH:MM'.

    Returns:
        Optional[datetime]: End datetime parsed from the window,
        or None if no pattern matched.
    """
    match = DOWNTIME_FORMAT_RE.search(downtime)
    if not match:
        logger.warning(f'Failed to parse downtime window: {downtime}')
        return None
    year, month, day = int(match.group(1)), int(match.group(2)), int(match.group(3))
    end_hour, end_minute = int(match.group(6)), int(match.group(7))
    end_dt = datetime(year, month, day, end_hour, end_minute)
    logger.info(f'Parsed downtime window: end={end_dt:%Y-%m-%d %H:%M}')
    return end_dt