import { googleCalendarAuth } from './auth';
import { startOfMonth, endOfMonth, format } from 'date-fns';

const CALENDAR_API_BASE = 'https://www.googleapis.com/calendar/v3';

export interface CalendarEvent {
  id: string;
  summary: string;
  description?: string;
  location?: string;
  start: {
    dateTime?: string;
    date?: string;
    timeZone?: string;
  };
  end: {
    dateTime?: string;
    date?: string;
    timeZone?: string;
  };
  status: string;
  colorId?: string;
}

export interface Calendar {
  id: string;
  summary: string;
  description?: string;
  primary?: boolean;
  backgroundColor?: string;
  foregroundColor?: string;
}

export interface CalendarListResponse {
  items: Calendar[];
}

export interface EventsListResponse {
  items: CalendarEvent[];
  nextPageToken?: string;
}

async function fetchWithAuth(url: string): Promise<Response> {
  const token = await googleCalendarAuth.getAccessToken();
  if (!token) {
    throw new Error('Not authenticated with Google Calendar');
  }

  const response = await fetch(url, {
    headers: {
      Authorization: `Bearer ${token}`,
    },
  });

  if (response.status === 401) {
    // Token might be invalid, clear and throw
    googleCalendarAuth.clearTokens();
    throw new Error('Authentication expired, please re-authenticate');
  }

  if (!response.ok) {
    throw new Error(`Calendar API error: ${response.status}`);
  }

  return response;
}

export async function getCalendarList(): Promise<Calendar[]> {
  const response = await fetchWithAuth(`${CALENDAR_API_BASE}/users/me/calendarList`);
  const data: CalendarListResponse = await response.json();
  return data.items;
}

export async function getEventsForMonth(
  calendarId: string = 'primary',
  date: Date = new Date()
): Promise<CalendarEvent[]> {
  const timeMin = startOfMonth(date).toISOString();
  const timeMax = endOfMonth(date).toISOString();

  const params = new URLSearchParams({
    timeMin,
    timeMax,
    singleEvents: 'true',
    orderBy: 'startTime',
    maxResults: '100',
  });

  const url = `${CALENDAR_API_BASE}/calendars/${encodeURIComponent(calendarId)}/events?${params}`;
  const response = await fetchWithAuth(url);
  const data: EventsListResponse = await response.json();
  return data.items;
}

export async function getEventsForDay(
  calendarId: string = 'primary',
  date: Date = new Date()
): Promise<CalendarEvent[]> {
  const dayStart = new Date(date);
  dayStart.setHours(0, 0, 0, 0);

  const dayEnd = new Date(date);
  dayEnd.setHours(23, 59, 59, 999);

  const params = new URLSearchParams({
    timeMin: dayStart.toISOString(),
    timeMax: dayEnd.toISOString(),
    singleEvents: 'true',
    orderBy: 'startTime',
  });

  const url = `${CALENDAR_API_BASE}/calendars/${encodeURIComponent(calendarId)}/events?${params}`;
  const response = await fetchWithAuth(url);
  const data: EventsListResponse = await response.json();
  return data.items;
}

export function getEventTime(event: CalendarEvent): { start: Date; end: Date; allDay: boolean } {
  const allDay = !!event.start.date;

  let start: Date;
  let end: Date;

  if (allDay) {
    start = new Date(event.start.date!);
    end = new Date(event.end.date!);
  } else {
    start = new Date(event.start.dateTime!);
    end = new Date(event.end.dateTime!);
  }

  return { start, end, allDay };
}

export function formatEventTime(event: CalendarEvent): string {
  const { start, allDay } = getEventTime(event);

  if (allDay) {
    return 'All day';
  }

  return format(start, 'h:mm a');
}