import calendar
from dataclasses import dataclass
from datetime import date, datetime
from typing import Generator

import pytz
import streamlit as st
from googleapiclient.discovery import build


def build_calendar_api(creds):
    return build("calendar", "v3", credentials=creds)


@dataclass
class Event:
    id: str
    title: str
    description: str | None
    start: datetime


@st.cache_data(ttl=60, show_spinner="Fetching calendars...")
def get_calendars(_service):
    calendars = []
    page_token = None
    while True:
        calendar_list = _service.calendarList().list(pageToken=page_token).execute()
        for entry in calendar_list["items"]:
            cal_id = entry["id"]
            calendars.append(cal_id)
        page_token = calendar_list.get("nextPageToken")
        if not page_token:
            break

    return calendars


def localize(date_input: datetime | date) -> datetime:
    local_timezone = pytz.timezone("America/Los_Angeles")
    timezone_aware_datetime = local_timezone.localize(
        datetime(date_input.year, date_input.month, date_input.day)
    )
    utc_datetime = timezone_aware_datetime.astimezone(pytz.utc)
    return utc_datetime


@st.cache_data(ttl=60, show_spinner="Fetching calendar events...")
def get_events(
    _service,
    start: datetime | date,
    end: datetime | date,
    calendar_ids: list[str],
) -> list[Event]:
    all_events: list[Event] = []
    for cal_id in calendar_ids:
        all_events.extend(
            _gen_events(
                _service,
                calendarId=cal_id,
                timeMin=localize(start).isoformat(),
                timeMax=localize(end).isoformat(),
                singleEvents=True,
                orderBy="startTime",
            )
        )
    all_events.sort(key=lambda ev: ev.start)
    return all_events


def _gen_events(_service, **kwargs) -> Generator[Event, None, None]:
    page_token = None
    while True:
        events = (
            _service.events()
            .list(
                **kwargs,
                pageToken=page_token,
            )
            .execute()
        )
        for event in events["items"]:
            start = _parse_date(event["start"])
            ev = Event(
                id=event["id"],
                title=event["summary"],
                description=event.get("description"),
                start=start,
            )
            yield ev

        page_token = events.get("nextPageToken")
        if not page_token:
            break


def _parse_date(date_obj: dict) -> datetime:
    if "dateTime" in date_obj:
        dt = datetime.fromisoformat(date_obj["dateTime"].rstrip("Z"))

    elif "date" in date_obj:
        dt = datetime.fromisoformat(date_obj["date"])
    else:
        raise ValueError("Event has no start date")

    is_naive = dt.tzinfo is None or dt.tzinfo.utcoffset(dt) is None
    if is_naive:
        if "timeZone" in date_obj:
            timezone = pytz.timezone(date_obj["timeZone"])
            dt = timezone.localize(dt)
        else:
            dt = pytz.utc.localize(dt)

    return dt


def get_start_and_end(month_date: date) -> tuple[date, date]:
    start_of_month = date(month_date.year, month_date.month, 1)
    last_day_of_month = calendar.monthrange(month_date.year, month_date.month)[1]
    end_of_month = date(month_date.year, month_date.month, last_day_of_month)
    return start_of_month, end_of_month