/**
 * utils/graphMailer.js
 * Invia email tramite Microsoft Graph API (per Exchange con 2FA/OAuth2).
 * Gestisce automaticamente il token OAuth2 con cache e refresh.
 */
'use strict';

let cachedToken = null;
let tokenExpiresAt = 0;

/**
 * Ottiene un access token OAuth2 da Microsoft (client credentials flow).
 * Il token viene cachato per circa 55 minuti per evitare richieste continue.
 */
async function getAccessToken() {
  const now = Date.now();
  if (cachedToken && now < tokenExpiresAt) {
    return cachedToken;
  }

  const { AZURE_TENANT_ID, AZURE_CLIENT_ID, AZURE_CLIENT_SECRET } = process.env;

  const url = `https://login.microsoftonline.com/${AZURE_TENANT_ID}/oauth2/v2.0/token`;

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

  const res = await fetch(url, {
    method: 'POST',
    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
    body: body.toString(),
  });

  if (!res.ok) {
    const errText = await res.text();
    throw new Error(`[Graph Auth] Errore ottenendo token OAuth2: ${res.status} ${errText}`);
  }

  const data = await res.json();
  cachedToken = data.access_token;
  // Scade in data.expires_in secondi, refresh 5 minuti prima
  tokenExpiresAt = now + (data.expires_in - 300) * 1000;
  return cachedToken;
}

/**
 * Invia una email tramite Microsoft Graph API.
 *
 * @param {Object} options
 * @param {string[]} options.to - Destinatari (array di email)
 * @param {string[]} [options.cc] - CC (array di email)
 * @param {string[]} [options.bcc] - BCC (array di email)
 * @param {string} options.subject - Oggetto email
 * @param {string} options.bodyHtml - Corpo HTML
 * @param {Array}  [options.attachments] - [{ filename, content (base64), contentType }]
 * @param {Array}  [options.inlineImages] - [{ cid, content (base64), contentType }]
 * @returns {Promise<void>}
 */
async function sendMail({ to, cc = [], bcc = [], subject, bodyHtml, attachments = [], inlineImages = [], inReplyTo, references, messageId }) {
  const sender = process.env.AZURE_MAIL_SENDER;
  if (!sender) throw new Error('AZURE_MAIL_SENDER non configurato nel .env');

  const token = await getAccessToken();

  const toRecipients = to.map(addr => ({
    emailAddress: { address: addr }
  }));
  const ccRecipients = cc.map(addr => ({
    emailAddress: { address: addr }
  }));
  const bccRecipients = bcc.map(addr => ({
    emailAddress: { address: addr }
  }));

  // Costruisce gli allegati (file + immagini inline)
  const allAttachments = [
    ...attachments.map(a => ({
      '@odata.type': '#microsoft.graph.fileAttachment',
      name: a.filename,
      contentType: a.contentType || 'application/octet-stream',
      contentBytes: a.content, // già base64
    })),
    ...inlineImages.map(img => ({
      '@odata.type': '#microsoft.graph.fileAttachment',
      name: img.cid,
      contentId: img.cid,
      contentType: img.contentType || 'image/png',
      contentBytes: img.content, // già base64
      isInline: true,
    })),
  ];

  const headers = [];
  if (inReplyTo) {
    headers.push({ name: 'In-Reply-To', value: inReplyTo });
  }
  if (references) {
    headers.push({ name: 'References', value: references });
  }

  const payload = {
    message: {
      subject,
      body: {
        contentType: 'HTML',
        content: bodyHtml,
      },
      toRecipients,
      ccRecipients,
      bccRecipients,
      attachments: allAttachments,
      internetMessageHeaders: headers.length ? headers : undefined,
    },
    saveToSentItems: true,
  };

  const url = `https://graph.microsoft.com/v1.0/users/${encodeURIComponent(sender)}/sendMail`;

  const res = await fetch(url, {
    method: 'POST',
    headers: {
      'Authorization': `Bearer ${token}`,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify(payload),
  });

  if (res.status === 202) {
    let actualMessageId = messageId;
    try {
      // Wait 1.5 seconds for Exchange to process and place it in Sent Items
      await new Promise(resolve => setTimeout(resolve, 1500));

      const searchUrl = `https://graph.microsoft.com/v1.0/users/${encodeURIComponent(sender)}/mailFolders/sentItems/messages?$filter=subject eq '${subject.replace(/'/g, "''")}'&$top=1&$select=internetMessageId`;
      const searchRes = await fetch(searchUrl, {
        headers: {
          'Authorization': `Bearer ${token}`,
          'Content-Type': 'application/json'
        }
      });

      if (searchRes.ok) {
        const searchData = await searchRes.json();
        if (searchData.value && searchData.value.length > 0) {
          actualMessageId = searchData.value[0].internetMessageId;
        }
      }
    } catch (searchErr) {
      console.warn('[Graph Mailer] Failed to retrieve actual InternetMessageId from Sent Items:', searchErr.message);
    }

    return { internetMessageId: actualMessageId };
  }

  const errText = await res.text();
  throw new Error(`[Graph Mail] Errore invio email: ${res.status} ${errText}`);
}

module.exports = { sendMail };