from __future__ import annotations

from dataclasses import dataclass
from datetime import datetime
from typing import Any


@dataclass(frozen=True)
class AvailabilityResult:
    start: str
    end: str
    available: bool
    busy_slots: list[dict[str, str]]
    checked_calendars: list[str]


class CalendarAvailabilityAgent:
    def __init__(self, calendar_service: Any) -> None:
        self.calendar_service = calendar_service

    def get_availability(
        self, start: str, end: str, calendar_ids: list[str] | None = None
    ) -> AvailabilityResult:
        start_dt = _parse_iso_datetime(start)
        end_dt = _parse_iso_datetime(end)

        if end_dt <= start_dt:
            raise ValueError("end must be after start.")

        calendars = calendar_ids or ["primary"]
        query_body = {
            "timeMin": start_dt.isoformat(),
            "timeMax": end_dt.isoformat(),
            "items": [{"id": calendar_id} for calendar_id in calendars],
        }

        freebusy = self.calendar_service.freebusy().query(body=query_body).execute()
        calendars_payload = freebusy.get("calendars", {})

        busy_slots: list[dict[str, str]] = []
        for calendar_id, data in calendars_payload.items():
            for busy_slot in data.get("busy", []):
                busy_slots.append(
                    {
                        "calendar_id": calendar_id,
                        "start": busy_slot["start"],
                        "end": busy_slot["end"],
                    }
                )

        return AvailabilityResult(
            start=start_dt.isoformat(),
            end=end_dt.isoformat(),
            available=len(busy_slots) == 0,
            busy_slots=busy_slots,
            checked_calendars=calendars,
        )


def _parse_iso_datetime(value: str) -> datetime:
    normalized = value.strip()
    if normalized.endswith("Z"):
        normalized = normalized[:-1] + "+00:00"

    parsed = datetime.fromisoformat(normalized)
    if parsed.tzinfo is None:
        raise ValueError("datetime must include a timezone offset, for example +01:00.")
    return parsed