"""Handover time parsing for duty schedule import."""

import re
from datetime import datetime, timezone

# HH:MM or HH:MM:SS, optional space + timezone (IANA or "UTC")
HANDOVER_TIME_RE = re.compile(
    r"^\s*(\d{1,2}):(\d{2})(?::(\d{2}))?\s*(?:\s+(\S+))?\s*$", re.IGNORECASE
)


def parse_handover_time(text: str) -> tuple[int, int] | None:
    """Parse handover time string to (hour_utc, minute_utc). Returns None on failure."""
    m = HANDOVER_TIME_RE.match(text)
    if not m:
        return None
    hour = int(m.group(1))
    minute = int(m.group(2))
    # second = m.group(3) ignored
    tz_str = (m.group(4) or "").strip()
    if not tz_str or tz_str.upper() == "UTC":
        return (hour % 24, minute)
    try:
        from zoneinfo import ZoneInfo
    except ImportError:
        try:
            from backports.zoneinfo import ZoneInfo  # type: ignore
        except ImportError:
            return None
    try:
        tz = ZoneInfo(tz_str)
    except Exception:
        return None
    # Build datetime in that tz and convert to UTC
    dt = datetime(2000, 1, 1, hour, minute, 0, tzinfo=tz)
    utc = dt.astimezone(timezone.utc)
    return (utc.hour, utc.minute)