import { NodeHtmlMarkdown } from 'node-html-markdown';

export interface CalendarEvent {
  id: string;
  subject: string;
  start: string; // "HH:MM"
  end: string;   // "HH:MM"
  body: string;
  attendees: { name: string; email: string }[];
}

interface AppTokenEntry {
  accessToken: string;
  expiresAt: number; // ms
}

let appTokenCache: AppTokenEntry | null = null;

const tenantId = process.env.AZURE_TENANT_ID ?? '';
const graphClientId = process.env.AZURE_GRAPH_CLIENT_ID ?? '';
const graphClientSecret = process.env.AZURE_GRAPH_CLIENT_SECRET ?? '';

async function getAppToken(): Promise<string> {
  if (appTokenCache && appTokenCache.expiresAt > Date.now() + 60_000) {
    return appTokenCache.accessToken;
  }

  if (!tenantId || !graphClientId || !graphClientSecret) {
    throw new Error(`Graph config incomplete: tenantId=${!!tenantId} clientId=${!!graphClientId} secret=${!!graphClientSecret}`);
  }

  const body = new URLSearchParams({
    client_id: graphClientId,
    client_secret: graphClientSecret,
    grant_type: 'client_credentials',
    scope: 'https://graph.microsoft.com/.default',
  });

  const res = await fetch(
    `https://login.microsoftonline.com/${tenantId}/oauth2/v2.0/token`,
    { method: 'POST', headers: { 'Content-Type': 'application/x-www-form-urlencoded' }, body },
  );

  if (!res.ok) {
    const detail = await res.text();
    console.error(`[graph] app token exchange failed ${res.status}: ${detail}`);
    throw new Error(`Graph app token exchange failed (${res.status}): ${detail}`);
  }

  const json = await res.json() as { access_token: string; expires_in: number };
  appTokenCache = {
    accessToken: json.access_token,
    expiresAt: Date.now() + json.expires_in * 1000,
  };
  console.log(`[graph] app token obtained, expires_in=${json.expires_in}s`);
  return appTokenCache.accessToken;
}

function toHHMM(dateTime: string): string {
  // Graph returns local time when Prefer: outlook.timezone header is set
  return dateTime.slice(11, 16);
}

export async function getCalendarEvents(
  userEmail: string,
  date: string,
): Promise<CalendarEvent[]> {
  console.log(`[graph] getCalendarEvents email=${userEmail} date=${date}`);
  const graphToken = await getAppToken();

  const start = `${date}T00:00:00`;
  const end = `${date}T23:59:59`;
  const select = 'id,subject,start,end,body,attendees,isAllDay';
  const url =
    `https://graph.microsoft.com/v1.0/users/${encodeURIComponent(userEmail)}/calendarView` +
    `?startDateTime=${encodeURIComponent(start)}` +
    `&endDateTime=${encodeURIComponent(end)}` +
    `&$select=${select}` +
    `&$top=50`;

  const timezone = process.env.CALENDAR_TIMEZONE ?? 'Europe/Berlin';

  const res = await fetch(url, {
    headers: {
      Authorization: `Bearer ${graphToken}`,
      'Content-Type': 'application/json',
      'Prefer': `outlook.timezone="${timezone}"`,
    },
  });

  if (!res.ok) {
    const detail = await res.text();
    console.error(`[graph] calendarView failed ${res.status}: ${detail}`);
    throw new Error(`Graph calendarView failed (${res.status}): ${detail}`);
  }
  console.log(`[graph] calendarView OK`);

  const CAUTION_BANNER = /CAUTION:\s*This email is from outside the organization\.[^]*?content is safe\./gi;

  function cleanBody(raw: string, contentType: string): string {
    const md = contentType === 'html'
      ? NodeHtmlMarkdown.translate(raw)
      : raw;
    return md
      .replace(CAUTION_BANNER, '')
      .replace(/(?:\\?[-_=*~]){10,}/g, '\n\n---\n\n')
      .replace(/\n{3,}/g, '\n\n')
      .trim();
  }

  type GraphEvent = {
    id: string;
    subject: string;
    start: { dateTime: string };
    end: { dateTime: string };
    body: { contentType: string; content: string };
    isAllDay: boolean;
    attendees: { emailAddress: { name: string; address: string }; type: string }[];
  };

  const data = await res.json() as { value: GraphEvent[] };

  return data.value
    .filter((e) => !e.isAllDay)
    .map((e) => ({
      id: e.id,
      subject: e.subject ?? '',
      start: toHHMM(e.start.dateTime),
      end: toHHMM(e.end.dateTime),
      body: cleanBody(e.body?.content ?? '', e.body?.contentType ?? 'text'),
      attendees: (e.attendees ?? [])
        .filter((a) => a.emailAddress.address.toLowerCase() !== userEmail.toLowerCase())
        .map((a) => ({ name: a.emailAddress.name, email: a.emailAddress.address })),
    }))
    .sort((a, b) => a.start.localeCompare(b.start));
}