/**
 * Gmail service – OAuth client, send reply, send ticket-closed email.
 */
const { google } = require('googleapis');
const { CONFIG } = require('../config');
const { extractRawEmail } = require('../utils');

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 });
}

async function sendGmailReply(
  threadId,
  replyText,
  recipientEmail,
  subject,
  discordUser,
  messageId
) {
  const gmail = getGmailClient();

  const utf8Subject = `=?utf-8?B?${Buffer.from(
    `Re: ${subject}`
  ).toString('base64')}?=`;
  const htmlBody = `
    <div style="font-family: sans-serif; font-size: 14px; color: #333;">
      <p><strong>From:</strong> ${discordUser} on Discord</p>
      <p>${replyText.replace(/\n/g, '<br>')}</p>
      <hr style="border:none; border-top:1px solid #ddd; margin:20px 0;">
      <table border="0" cellpadding="0" cellspacing="0">
        <tr>
          <td style="padding-right: 12px;">
            <img src="${CONFIG.LOGO_URL}" width="65">
          </td>
          <td style="border-left: 1px solid #ddd; padding-left: 12px;">
            <p style="margin: 0; font-weight: bold;">${discordUser}</p>
            <div style="color: #666; font-size: 12px;">${CONFIG.SIGNATURE}</div>
          </td>
        </tr>
      </table>
    </div>`;

  const headers = [
    `From: ${CONFIG.MY_EMAIL}`,
    `To: ${recipientEmail}`,
    `Subject: ${utf8Subject}`,
    messageId ? `In-Reply-To: ${messageId}` : '',
    messageId ? `References: ${messageId}` : '',
    'MIME-Version: 1.0',
    'Content-Type: text/html; charset="UTF-8"',
    '',
    htmlBody
  ].filter(Boolean);

  const raw = Buffer.from(headers.join('\r\n'))
    .toString('base64')
    .replace(/\+/g, '-')
    .replace(/\//g, '_')
    .replace(/=+$/, '');

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

async function sendTicketClosedEmail(ticket, discordDisplayName) {
  try {
    const gmail = getGmailClient();

    // Send to the ticket sender (customer), not derived from thread (which can be support)
    const recipientEmail = extractRawEmail(ticket.senderEmail || '').toLowerCase();
    if (!recipientEmail || recipientEmail === CONFIG.MY_EMAIL) return;

    let subjectHeader = ticket.subject || 'Support';
    let msgId = null;
    try {
      const thread = await gmail.users.threads.get({
        userId: 'me',
        id: ticket.gmailThreadId
      });
      const messages = thread.data.messages || [];
      const lastMsg = [...messages].reverse()[0];
      if (lastMsg?.payload?.headers) {
        const subj = lastMsg.payload.headers.find(h => h.name === 'Subject')?.value;
        if (subj) subjectHeader = subj;
        msgId = lastMsg.payload.headers.find(h => h.name === 'Message-ID')?.value;
      }
    } catch (_) {
      /* use ticket.subject and no In-Reply-To if thread fetch fails */
    }

    const finalSubject = `${CONFIG.TICKET_CLOSE_SUBJECT_PREFIX} ${subjectHeader}`;
    const utf8Subject = `=?utf-8?B?${Buffer.from(
      finalSubject
    ).toString('base64')}?=`;

    const serverDisplayName = discordDisplayName || 'Support';

    const htmlBody = `
      <div style="font-family: sans-serif; font-size: 14px; color: #333;">
        <p><strong>From:</strong> ${serverDisplayName} on Discord</p>
        <p><strong>Message:</strong></p>
        <p>${CONFIG.TICKET_CLOSE_MESSAGE.replace(/\n/g, '<br>')}</p>
        <p style="margin-top: 16px;">${CONFIG.TICKET_CLOSE_SIGNATURE}</p>
        <hr style="border:none; border-top:1px solid #ddd; margin:20px 0;">
        <table border="0" cellpadding="0" cellspacing="0">
          <tr>
            <td style="padding-right: 12px;">
              <img src="${CONFIG.LOGO_URL}" width="65">
            </td>
            <td style="border-left: 1px solid #ddd; padding-left: 12px;">
              <p style="margin: 0; font-weight: bold;">${serverDisplayName}</p>
              <div style="color: #666; font-size: 12px;">${CONFIG.SIGNATURE}</div>
            </td>
          </tr>
        </table>
      </div>`;

    const rawHeaders = [
      `From: ${CONFIG.MY_EMAIL}`,
      `To: ${recipientEmail}`,
      `Subject: ${utf8Subject}`,
      msgId ? `In-Reply-To: ${msgId}` : '',
      msgId ? `References: ${msgId}` : '',
      'MIME-Version: 1.0',
      'Content-Type: text/html; charset="UTF-8"',
      '',
      htmlBody
    ].filter(Boolean);

    const raw = Buffer.from(rawHeaders.join('\r\n'))
      .toString('base64')
      .replace(/\+/g, '-')
      .replace(/\//g, '_')
      .replace(/=+$/, '');

    await gmail.users.messages.send({
      userId: 'me',
      requestBody: { raw, threadId: ticket.gmailThreadId }
    });
  } 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 - Subject line (e.g. "Ticket escalated" or "Priority updated")
 * @param {string} messageBody - Plain or HTML message body
 * @param {string} [fromLabel] - Label for "From" (e.g. "Support on Discord")
 */
async function sendTicketNotificationEmail(ticket, subjectLine, messageBody, fromLabel) {
  try {
    const gmail = getGmailClient();
    const recipientEmail = extractRawEmail(ticket.senderEmail || '').toLowerCase();
    if (!recipientEmail || recipientEmail === CONFIG.MY_EMAIL) return;

    let subjectHeader = ticket.subject || 'Support';
    let msgId = null;
    try {
      const thread = await gmail.users.threads.get({
        userId: 'me',
        id: ticket.gmailThreadId
      });
      const messages = thread.data.messages || [];
      const lastMsg = [...messages].reverse()[0];
      if (lastMsg?.payload?.headers) {
        const subj = lastMsg.payload.headers.find(h => h.name === 'Subject')?.value;
        if (subj) subjectHeader = subj;
        msgId = lastMsg.payload.headers.find(h => h.name === 'Message-ID')?.value;
      }
    } catch (_) {}

    const finalSubject = subjectLine || subjectHeader;
    const utf8Subject = `=?utf-8?B?${Buffer.from(finalSubject).toString('base64')}?=`;
    const label = fromLabel || CONFIG.SUPPORT_NAME || 'Support';
    const htmlBody = `
      <div style="font-family: sans-serif; font-size: 14px; color: #333;">
        <p><strong>From:</strong> ${label} on Discord</p>
        <p>${(messageBody || '').replace(/\n/g, '<br>')}</p>
        <hr style="border:none; border-top:1px solid #ddd; margin:20px 0;">
        <table border="0" cellpadding="0" cellspacing="0">
          <tr>
            <td style="padding-right: 12px;">
              <img src="${CONFIG.LOGO_URL}" width="65">
            </td>
            <td style="border-left: 1px solid #ddd; padding-left: 12px;">
              <p style="margin: 0; font-weight: bold;">${label}</p>
              <div style="color: #666; font-size: 12px;">${CONFIG.SIGNATURE}</div>
            </td>
          </tr>
        </table>
      </div>`;

    const rawHeaders = [
      `From: ${CONFIG.MY_EMAIL}`,
      `To: ${recipientEmail}`,
      `Subject: ${utf8Subject}`,
      msgId ? `In-Reply-To: ${msgId}` : '',
      msgId ? `References: ${msgId}` : '',
      'MIME-Version: 1.0',
      'Content-Type: text/html; charset="UTF-8"',
      '',
      htmlBody
    ].filter(Boolean);

    const raw = Buffer.from(rawHeaders.join('\r\n'))
      .toString('base64')
      .replace(/\+/g, '-')
      .replace(/\//g, '_')
      .replace(/=+$/, '');

    await gmail.users.messages.send({
      userId: 'me',
      requestBody: { raw, threadId: ticket.gmailThreadId }
    });
  } catch (err) {
    console.error('Ticket notification email error:', err);
  }
}

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