const { ConfidentialClientApplication } = require('@azure/msal-node');
const { Client } = require('@microsoft/microsoft-graph-client');
const { readFileSync } = require('node:fs');
const { resolve } = require('node:path');

function loadEnv() {
  const envPath = resolve(__dirname, '..', '.env');
  const content = readFileSync(envPath, 'utf-8');
  const vars = {};
  for (const line of content.split('\n')) {
    const trimmed = line.trim();
    if (!trimmed || trimmed.startsWith('#')) continue;
    const [key, ...rest] = trimmed.split('=');
    vars[key.trim()] = rest.join('=').trim();
  }
  return vars;
}

function stripHtml(html) {
  return html
    .replace(/<br\s*\/?>/gi, '\n')
    .replace(/<\/p>/gi, '\n')
    .replace(/<[^>]+>/g, '')
    .replace(/&nbsp;/g, ' ')
    .replace(/&amp;/g, '&')
    .replace(/&lt;/g, '<')
    .replace(/&gt;/g, '>')
    .replace(/\n{3,}/g, '\n\n')
    .trim();
}

function isRecurring(event) {
  return Boolean(event.seriesMasterId);
}

function parseEventToMeeting(event) {
  const startDate = event.start.dateTime.split('T');
  const endDate = event.end.dateTime.split('T');

  return {
    id: event.id,
    title: event.subject,
    date: startDate[0],
    start: startDate[1].substring(0, 5),
    end: endDate[1].substring(0, 5),
    bodyText: event.body?.contentType === 'html'
      ? stripHtml(event.body.content)
      : (event.body?.content || '').trim(),
    attendees: (event.attendees || []).map(a => ({
      name: a.emailAddress.name,
      email: a.emailAddress.address.toLowerCase()
    })),
    isRecurring: isRecurring(event)
  };
}

function formatEventChoice(meeting) {
  return `📅 ${meeting.date} ${meeting.start}-${meeting.end} ${meeting.title}`;
}

async function buildAuthenticatedClient() {
  const env = loadEnv();

  const cca = new ConfidentialClientApplication({
    auth: {
      clientId: env.AZURE_CLIENT_ID,
      clientSecret: env.AZURE_CLIENT_SECRET,
      authority: `https://login.microsoftonline.com/${env.AZURE_TENANT_ID}`
    }
  });

  const tokenResponse = await cca.acquireTokenByClientCredential({
    scopes: ['https://graph.microsoft.com/.default']
  });

  return Client.init({
    authProvider: (done) => done(null, tokenResponse.accessToken)
  });
}

async function getCalendarEvents(daysAhead = 7) {
  const env = loadEnv();
  const client = await buildAuthenticatedClient();

  const now = new Date();
  const future = new Date(now);
  future.setDate(future.getDate() + daysAhead);

  const response = await client
    .api(`/users/${env.AZURE_USER_EMAIL}/calendarView`)
    .query({
      startDateTime: now.toISOString(),
      endDateTime: future.toISOString()
    })
    .select('id,subject,start,end,body,attendees,seriesMasterId')
    .orderby('start/dateTime')
    .top(500)
    .get();

  return (response.value || []).map(parseEventToMeeting);
}

function extractJoinUrlFromBody(body) {
  if (!body) return null;
  const m = body.match(/https:\/\/teams\.microsoft\.com\/l\/meetup-join\/[^\s"'<>]+/);
  return m ? m[0] : null;
}

async function getEventById(eventId) {
  if (typeof eventId !== 'string' || !eventId.trim()) {
    throw new TypeError('eventId must be a non-empty string');
  }

  try {
    const env = loadEnv();
    const client = await buildAuthenticatedClient();

    const event = await client
      .api(`/users/${env.AZURE_USER_EMAIL}/events/${eventId}`)
      .select('id,subject,start,end,body,attendees,seriesMasterId,onlineMeeting')
      .get();
    return event;
  } catch (cause) {
    throw new Error(`Failed to fetch event ${eventId}: ${cause.message}`, { cause });
  }
}

module.exports = {
  isRecurring, parseEventToMeeting, formatEventChoice,
  getCalendarEvents, getEventById, extractJoinUrlFromBody
};