"""Generate ICS calendar containing only one user's duties (for subscription link)."""

from datetime import datetime, timezone

from icalendar import Calendar, Event

from duty_teller.db.models import Duty

# Summary labels by event_type (duty | unavailable | vacation)
SUMMARY_BY_TYPE: dict[str, str] = {
    "duty": "Duty",
    "unavailable": "Unavailable",
    "vacation": "Vacation",
}


def _parse_utc_iso(iso_str: str) -> datetime:
    """Parse ISO 8601 UTC string (e.g. 2025-01-15T09:00:00Z) to timezone-aware datetime."""
    s = iso_str.strip().rstrip("Z")
    if "Z" in s:
        s = s.replace("Z", "+00:00")
    else:
        s = s + "+00:00"
    return datetime.fromisoformat(s)


def build_personal_ics(duties_with_name: list[tuple[Duty, str]]) -> bytes:
    """
    Build a single VCALENDAR with one VEVENT per duty.
    duties_with_name: list of (Duty, full_name); full_name is unused for SUMMARY
    if we use event_type only; can be used later for DESCRIPTION.
    """
    cal = Calendar()
    cal.add("prodid", "-//Duty Teller//Personal Calendar//EN")
    cal.add("version", "2.0")
    cal.add("calscale", "GREGORIAN")

    for duty, _full_name in duties_with_name:
        event = Event()
        start_dt = _parse_utc_iso(duty.start_at)
        end_dt = _parse_utc_iso(duty.end_at)
        # Ensure timezone-aware for icalendar
        if start_dt.tzinfo is None:
            start_dt = start_dt.replace(tzinfo=timezone.utc)
        if end_dt.tzinfo is None:
            end_dt = end_dt.replace(tzinfo=timezone.utc)
        event.add("dtstart", start_dt)
        event.add("dtend", end_dt)
        summary = SUMMARY_BY_TYPE.get(
            duty.event_type if duty.event_type else "duty", "Duty"
        )
        event.add("summary", summary)
        event.add("uid", f"duty-{duty.id}@duty-teller")
        event.add("dtstamp", datetime.now(timezone.utc))
        cal.add_component(event)

    return cal.to_ical()