'use strict';

/**
 * IMAP ID 注入代理（专治 163 "Unsafe Login"）
 *
 * 背景：LibreDesk 的 go-imap 客户端不发 IMAP ID 命令，163 会在 SELECT 时返回
 *   "NO SELECT Unsafe Login"，导致邮箱无法收取。
 *
 * 本代理：明文监听 1993，TLS 连接上游 imap.163.com:993；
 * 在客户端发 SELECT/EXAMINE 之前，自动发送一条 ID 命令并吞掉它的响应。
 * 仅用于本地/内网 POC，不要在公网暴露。
 */
const net = require('net');
const tls = require('tls');

const LISTEN_PORT = Number(process.env.LISTEN_PORT || 1993);
const UPSTREAM_HOST = process.env.UPSTREAM_HOST || 'imap.163.com';
const UPSTREAM_PORT = Number(process.env.UPSTREAM_PORT || 993);
const ID_LINE = process.env.ID_LINE || '("name" "libredesk" "version" "2.9" "vendor" "libredesk")';

let connSeq = 0;

function log(...args) {
  console.log(new Date().toISOString(), '[imap-id-proxy]', ...args);
}

function pipeLineSplitter(onLine) {
  let buf = '';
  return {
    push(chunk) {
      buf += chunk.toString('latin1');
      let idx;
      while ((idx = buf.indexOf('\r\n')) >= 0) {
        const line = buf.slice(0, idx);
        buf = buf.slice(idx + 2);
        onLine(line);
      }
    },
  };
}

const server = net.createServer((client) => {
  const id = ++connSeq;
  const tag = `P${id}`;
  let injected = false;
  let waitingId = false;
  const pendingFromClient = [];
  let upstreamWrite = null;

  log(`conn ${id} opened`);

  const upstream = tls.connect({ host: UPSTREAM_HOST, port: UPSTREAM_PORT, servername: UPSTREAM_HOST }, () => {
    log(`conn ${id} upstream TLS ready`);
  });
  upstream.setEncoding('latin1');
  client.setEncoding('latin1');

  upstreamWrite = (line) => upstream.write(`${line}\r\n`);

  const clientLines = pipeLineSplitter((line) => {
    const upper = line.toUpperCase();
    const isMailboxCmd = /^\S+\s+(SELECT|EXAMINE)\b/.test(upper);
    if (!injected && isMailboxCmd) {
      injected = true;
      waitingId = true;
      pendingFromClient.push(line);
      log(`conn ${id} injecting ID before: ${line.slice(0, 40)}`);
      upstream.write(`${tag} ID ${ID_LINE}\r\n`);
      return;
    }
    if (waitingId) {
      pendingFromClient.push(line);
      return;
    }
    upstream.write(`${line}\r\n`);
  });

  const upstreamLines = pipeLineSplitter((line) => {
    if (waitingId) {
      if (line.startsWith('* ID ')) return; // 吞掉 untagged ID 响应
      if (/^P\d+\s+(OK|NO|BAD)\b/i.test(line)) {
        const ok = /^P\d+\s+OK\b/i.test(line);
        log(`conn ${id} ID response: ${line.slice(0, 60)}`);
        waitingId = false;
        if (!ok) {
          // ID 被拒也继续转发，让上层自己报错
          client.write(`${line}\r\n`);
        }
        while (pendingFromClient.length) upstream.write(`${pendingFromClient.shift()}\r\n`);
        return;
      }
      // 其它服务器响应（如 * OK）先转发
      client.write(`${line}\r\n`);
      return;
    }
    client.write(`${line}\r\n`);
  });

  client.on('data', (chunk) => clientLines.push(chunk));
  upstream.on('data', (chunk) => upstreamLines.push(chunk));

  const close = (why) => {
    log(`conn ${id} closed (${why})`);
    client.destroy();
    upstream.destroy();
  };
  client.on('error', (e) => close(`client error ${e.message}`));
  upstream.on('error', (e) => {
    log(`conn ${id} upstream error ${e.message}`);
    client.destroy();
  });
  client.on('close', () => upstream.destroy());
  upstream.on('close', () => client.destroy());
});

server.listen(LISTEN_PORT, '0.0.0.0', () => {
  log(`listening :${LISTEN_PORT} -> ${UPSTREAM_HOST}:${UPSTREAM_PORT} (TLS)`);
});