/**
 * Gmail service – OAuth client, send reply, send ticket-closed/notification emails.
 */
const { google } = require('googleapis');
const { CONFIG } = require('../config');
const { extractRawEmail, escapeHtml } = require('../utils');
const { getStaffSignatureBlocks } = require('./staffSignature');
const { logError } = require('./debugLog');
const { readEnvFile } = require('./configPersistence');

function sanitizeHeaderValue(v) { return String(v || '').replace(/[\r\n]+/g, ' ').trim(); }
const EMAIL_RE = /^[^@\s]+@[^@\s]+$/;

function buildCompanySigHtml() {
  const safeLogoUrl = escapeHtml(CONFIG.LOGO_URL || '');
  return `
        <table border="0" cellpadding="0" cellspacing="0" style="margin-top: 16px;">
          <tr>
            <td style="padding-right: 12px; vertical-align: top;">
              ${safeLogoUrl ? `<img src="${safeLogoUrl}" width="65" alt="Indifferent Broccoli">` : ''}
            </td>
            <td style="border-left: 1px solid #ddd; padding-left: 12px; vertical-align: top; font-size: 13px; color: #333;">
              Indifferent Broccoli Support<br>
              <a href="https://indifferentbroccoli.com/">https://indifferentbroccoli.com/</a><br>
              Join us on <a href="https://discord.gg/2vmfrrtvJY">Discord</a><br>
              <br>
              <em>Host your own game server. Or not... we don't care.</em>
            </td>
          </tr>
        </table>`;
}

function buildCompanySigText() {
  return [
    'Indifferent Broccoli Support',
    'https://indifferentbroccoli.com/',
    'Join us on Discord: https://discord.gg/2vmfrrtvJY',
    '',
    "Host your own game server. Or not... we don't care."
  ].join('\n');
}

function getGmailClient() {
  const auth = new google.auth.OAuth2(
    process.env.GOOGLE_CLIENT_ID,
    process.env.GOOGLE_CLIENT_SECRET
  );
  auth.setCredentials({ refresh_token: CONFIG.REFRESH_TOKEN });
  return google.gmail({ version: 'v1', auth });
}

/**
 * Re-read REFRESH_TOKEN from .env, update in-memory config, and probe Google.
 * Used by the internal /gmail/reload endpoint so the weekly reauth chore does
 * not require a full container restart.
 *
 * Throws if the env file is missing the token, or if the probe call (getProfile)
 * fails — the caller surfaces the error so the UI can see why.
 */
async function reloadGmailClient() {
  const envMap = readEnvFile();
  const newToken = envMap.get('REFRESH_TOKEN');
  if (!newToken) {
    const err = new Error('REFRESH_TOKEN not set in .env');
    err.code = 'ENOTOKEN';
    throw err;
  }
  process.env.REFRESH_TOKEN = newToken;
  CONFIG.REFRESH_TOKEN = newToken;
  const gmail = getGmailClient();
  const profile = await gmail.users.getProfile({ userId: 'me' });
  return { emailAddress: profile.data.emailAddress };
}

// Fetch the first message's Subject + Message-ID from a Gmail thread, used to
// derive a faithful Re: subject and a proper In-Reply-To/References header.
async function fetchThreadSubjectAndMsgId(gmail, threadId) {
  try {
    const thread = await gmail.users.threads.get({ userId: 'me', id: threadId });
    const firstMsg = (thread.data.messages || [])[0];
    const headers = firstMsg?.payload?.headers || [];
    return {
      subject: headers.find(h => h.name === 'Subject')?.value || null,
      msgId: sanitizeHeaderValue(headers.find(h => h.name === 'Message-ID')?.value) || null
    };
  } catch (_) {
    return { subject: null, msgId: null };
  }
}

// Strip leading "Re:" variants and re-prepend a single one, then RFC 2047 encode.
function encodeReplySubject(baseSubject) {
  const stripped = String(baseSubject).replace(/^(?:\s*Re\s*:\s*)+/i, '');
  const safe = sanitizeHeaderValue(`Re: ${stripped}`);
  return `=?utf-8?B?${Buffer.from(safe).toString('base64')}?=`;
}

// Compose and send a multipart/alternative reply on an existing Gmail thread.
async function sendThreadedEmail(gmail, { threadId, recipient, encodedSubject, msgId, messageText, userId }) {
  const sigBlocks = userId ? await getStaffSignatureBlocks(userId) : { text: '', html: '' };
  const safeStaffSigHtml = sigBlocks.html ? sigBlocks.html.replace(/\n/g, '<br>') : '';
  const safeStaffSigText = sigBlocks.text;

  const htmlBody = `
    <div style="font-family: sans-serif; font-size: 14px; color: #333;">
      <p>${escapeHtml(messageText || '').replace(/\n/g, '<br>')}</p>
      ${safeStaffSigHtml ? `<p style="margin: 10px 0;">${safeStaffSigHtml}</p>` : ''}
      ${buildCompanySigHtml()}
    </div>`;

  const plainBody = [messageText || ''];
  if (safeStaffSigText) plainBody.push('', safeStaffSigText);
  plainBody.push('', ...buildCompanySigText().split('\n'));

  const boundary = '000000000000' + Date.now().toString(16);
  const headers = [
    `From: ${sanitizeHeaderValue(CONFIG.MY_EMAIL)}`,
    `To: ${recipient}`,
    `Subject: ${encodedSubject}`,
    msgId && `In-Reply-To: ${msgId}`,
    msgId && `References: ${msgId}`,
    'MIME-Version: 1.0',
    `Content-Type: multipart/alternative; boundary="${boundary}"`
  ].filter(Boolean);

  const raw = Buffer.from([
    ...headers,
    '',
    `--${boundary}`,
    'Content-Type: text/plain; charset="UTF-8"',
    '',
    ...plainBody,
    '',
    `--${boundary}`,
    'Content-Type: text/html; charset="UTF-8"',
    '',
    htmlBody,
    '',
    `--${boundary}--`
  ].join('\r\n'))
    .toString('base64')
    .replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');

  await gmail.users.messages.send({ userId: 'me', requestBody: { raw, threadId } });
}

// Resolve and validate a customer recipient from a ticket's senderEmail.
// Returns null and logs if invalid or self-addressed.
function resolveCustomerRecipient(ticket, context) {
  const recipientEmail = sanitizeHeaderValue(extractRawEmail(ticket.senderEmail || '')).toLowerCase();
  if (!recipientEmail || recipientEmail === CONFIG.MY_EMAIL) return null;
  if (!EMAIL_RE.test(recipientEmail)) {
    logError(`${context}: invalid recipient`, new Error(`Rejected: ${recipientEmail}`)).catch(() => {});
    return null;
  }
  return recipientEmail;
}

async function sendTicketClosedEmail(ticket, closerName, userId = null) {
  try {
    const recipient = resolveCustomerRecipient(ticket, 'sendTicketClosedEmail');
    if (!recipient) return;

    const gmail = getGmailClient();
    const { subject, msgId } = await fetchThreadSubjectAndMsgId(gmail, ticket.gmailThreadId);
    const encodedSubject = encodeReplySubject(subject || ticket.subject || 'Support');
    const messageText = `${closerName} has marked this ticket as resolved. If you would like to re-open this issue, please reply to this email.`;

    await sendThreadedEmail(gmail, {
      threadId: ticket.gmailThreadId,
      recipient,
      encodedSubject,
      msgId,
      messageText,
      userId
    });
  } catch (err) {
    console.error('Ticket closed email error:', err);
  }
}

/**
 * Send a notification email in the ticket thread (e.g. escalation, high-priority).
 * @param {Object} ticket - Ticket with gmailThreadId, senderEmail, subject
 * @param {string} subjectLine - Fallback subject if the thread can't be queried
 * @param {string} messageBody - Plain or HTML message body
 * @param {string} [userId] - Discord user ID for signature (optional)
 */
async function sendTicketNotificationEmail(ticket, subjectLine, messageBody, userId = null) {
  try {
    const recipient = resolveCustomerRecipient(ticket, 'sendTicketNotificationEmail');
    if (!recipient) return;

    const gmail = getGmailClient();
    const { subject, msgId } = await fetchThreadSubjectAndMsgId(gmail, ticket.gmailThreadId);
    const encodedSubject = encodeReplySubject(subject || subjectLine || ticket.subject || 'Support');

    await sendThreadedEmail(gmail, {
      threadId: ticket.gmailThreadId,
      recipient,
      encodedSubject,
      msgId,
      messageText: messageBody,
      userId
    });
  } catch (err) {
    console.error('Ticket notification email error:', err);
  }
}

/**
 * Send a Gmail reply on an existing thread. Caller supplies subject + messageId
 * (typically pulled from the latest non-self message in the thread).
 */
async function sendGmailReply(threadId, replyText, recipientEmail, subject, messageId, userId = null) {
  const safeRecipient = sanitizeHeaderValue(extractRawEmail(recipientEmail || '')).toLowerCase();
  if (!EMAIL_RE.test(safeRecipient)) {
    logError('sendGmailReply: invalid recipient', new Error(`Rejected: ${safeRecipient}`)).catch(() => {});
    return null;
  }

  const gmail = getGmailClient();
  await sendThreadedEmail(gmail, {
    threadId,
    recipient: safeRecipient,
    encodedSubject: encodeReplySubject(subject || 'Support'),
    msgId: sanitizeHeaderValue(messageId) || null,
    messageText: replyText,
    userId
  });
}

module.exports = {
  getGmailClient,
  reloadGmailClient,
  sendGmailReply,
  sendTicketClosedEmail,
  sendTicketNotificationEmail
};