// dump_plain.js - 把某个会话抓包解密成「明文帧」，供 fake 模式回放
// 用法: node dump_plain.js --session ../../packets/relay-04/session_005 [--out <目录>]
// 原理:
//   连接前半段是明文帧（可直接用），后半段是自变体 XOR 流密码加密帧；
//   密钥只有 1 字节，直接穷举 256 种，要求「该消息之后每条解密后都是完整帧」。
// 产物: <out>/<方向>_<序号>.bin（明文帧）+ <out>/summary.txt
const fs = require('fs');
const path = require('path');

const Argv = process.argv.slice(2);
const Arg = (Name, Def) => {
  const I = Argv.indexOf('--' + Name);
  return I >= 0 && Argv[I + 1] ? Argv[I + 1] : Def;
};

const SessionDir = path.resolve(Arg('session', ''));
const OutDir = path.resolve(Arg('out', path.join(SessionDir, 'plain')));
const CMD_NAME = {
  c2s: { 1: 'Hash Request', 3: 'Auth/EnterSpace', 32: 'ClientLog' },
  s2c: { 0: 'SpaceState(待证)', 2: 'Hash Response', 32: 'Open Space' },
};

function PeekFrame(Buf) {
  if (Buf.length < 2) return null;
  const B0 = Buf[0];
  if (B0 & 0x80) {
    if (Buf.length < 4) return null;
    return {
      TotalSize: 4 + ((((B0 & 0x3f) << 24) | (Buf[1] << 16) | (Buf[2] << 8) | Buf[3]) >>> 0),
      HeaderSize: 4,
      Compressed: (B0 & 0x40) !== 0,
    };
  }
  return { TotalSize: 2 + (((B0 & 0x3f) << 8) | Buf[1]), HeaderSize: 2, Compressed: (B0 & 0x40) !== 0 };
}

function IsFrames(Buf) {
  if (!Buf.length) return false;
  let Off = 0;
  while (Off < Buf.length) {
    const Info = PeekFrame(Buf.slice(Off));
    if (!Info || Off + Info.TotalSize > Buf.length) return false;
    Off += Info.TotalSize;
  }
  return true;
}

// 把一段连续字节流切成一帧帧；有任何残余则返回 null
function SplitFrames(Buf) {
  const Out = [];
  let Off = 0;
  while (Off < Buf.length) {
    const Info = PeekFrame(Buf.slice(Off));
    if (!Info || Off + Info.TotalSize > Buf.length) return null;
    Out.push(Buf.slice(Off, Off + Info.TotalSize));
    Off += Info.TotalSize;
  }
  return Out.length ? Out : null;
}

function NullmapSize(Buf, Offset) {
  const R = Buf[Offset];
  if (R === undefined) return 0;
  if ((R & 0x80) !== 0) {
    if (R & 0x40) return 4 + (((R & 0x3f) << 16) | (Buf[Offset + 1] << 8) | Buf[Offset + 2]);
    return 1 + (R & 0x3f);
  }
  return 1 + ((R & 0x60) >>> 5);
}

function CipherApply(Bufs, K, Encoded) {
  const Slot = new Int32Array(8);
  for (let I = 0; I < 8; I++) Slot[I] = ((K ^ (I << 3)) ^ (Encoded ? 87 : 0)) & 0xff;
  let Idx = 0;
  return Bufs.map((Buf) => {
    const Out = Buffer.alloc(Buf.length);
    for (let I = 0; I < Buf.length; I++) {
      const Plain = (Buf[I] ^ Slot[Idx]) & 0xff;
      Out[I] = Plain;
      Slot[Idx] = Plain;
      Idx = Idx ^ (Plain & 7);
    }
    return Out;
  });
}

// 返回 { Start, K, Frames:[{Buf, Msg}] }
// Msg = 该帧首字节落在第几条 WS 消息上（把帧映射回抓包时刻，供时间线回放）
// 注意：大帧会被拆到多条 WS 消息里，所以加密段要「拼接成流」再判帧
//
// 两个必须的护栏（否则会静默丢帧，实测 mine-01/session_001 59 条 c2s 全是明文整帧，
// 却被一个巧合的 K=31 判成「加密段只切出 1 帧」，结果只 dump 出 13 条）：
//   ① 若剩余部分的每条消息自身就是完整帧，就不再尝试解密（它们本来就是明文）→ 跳过这个 Start；
//   ② 多个候选起点都能解时取 Start 最大的那个（尽可能按明文处理；全明文会话会命中 Start = 消息数）。
function Solve(Bufs, Encoded) {
  let Best = null;
  for (let Start = 0; Start <= Bufs.length; Start++) {
    let Ok = true;
    for (let I = 0; I < Start; I++) if (!IsFrames(Bufs[I])) Ok = false;
    if (!Ok) continue;
    const Prefix = [];
    for (let I = 0; I < Start; I++) for (const F of SplitFrames(Bufs[I]) || []) Prefix.push({ Buf: F, Msg: I });
    if (Start === Bufs.length) {
      if (!Best || Start > Best.Start) Best = { Start, K: null, Frames: Prefix };
      continue;
    }
    const Rest = Bufs.slice(Start);
    if (Rest.every(IsFrames)) continue; // ① 剩余部分本来就是明文，别硬解
    const Hits = [];
    let WinFrames = null;
    for (let K = 0; K < 256; K++) {
      const Decoded = CipherApply(Rest, K, Encoded);
      const Fr = SplitFrames(Buffer.concat(Decoded));
      if (!Fr) continue;
      Hits.push(K);
      if (WinFrames) continue;
      // 每条消息在拼接流里的结束偏移，用于判断帧起点落在哪条消息
      const Bound = [];
      let Sum = 0;
      for (const B of Decoded) Bound.push((Sum += B.length));
      const Tagged = [];
      let Off = 0;
      for (const F of Fr) {
        let M = 0;
        while (M < Bound.length - 1 && Off >= Bound[M]) M++;
        Tagged.push({ Buf: F, Msg: Start + M });
        Off += F.length;
      }
      WinFrames = Prefix.concat(Tagged);
    }
    if (Hits.length === 1 && WinFrames && (!Best || Start > Best.Start)) Best = { Start, K: Hits[0], Frames: WinFrames };
  }
  return Best;
}

// 从 relay 的 log.txt 里取出某方向每条消息的到达时刻（毫秒）；无 log 时返回空数组
function ReadMessageTimes(SessionDir, Direction) {
  const LogPath = path.join(SessionDir, 'log.txt');
  if (!fs.existsSync(LogPath)) return [];
  const Out = [];
  for (const Line of fs.readFileSync(LogPath, 'utf8').split('\n')) {
    const M = /^\[([^\]]+)\]\s*(?:>>>|<<<)\s+(c2s|s2c)_(\d+)\.bin/.exec(Line.trim());
    if (!M || M[2] !== Direction) continue;
    Out.push({ Seq: Number(M[3]), Time: Date.parse(M[1]) });
  }
  Out.sort((A, B) => A.Seq - B.Seq);
  return Out;
}

function Describe(Buf) {
  const Info = PeekFrame(Buf);
  if (!Info || Info.TotalSize !== Buf.length) return '非法帧';
  const At = Info.HeaderSize + NullmapSize(Buf, Info.HeaderSize);
  if (At >= Buf.length) return '保活 ping';
  return '命令 ID=' + Buf[At];
}

if (!fs.existsSync(SessionDir)) {
  console.log('会话目录不存在: ' + SessionDir);
  process.exit(1);
}
fs.mkdirSync(OutDir, { recursive: true });
const Lines = ['来源会话: ' + SessionDir, ''];

for (const Direction of ['c2s', 's2c']) {
  const Files = fs
    .readdirSync(SessionDir)
    .filter((F) => new RegExp('^' + Direction + '_\\d+\\.bin$').test(F))
    .sort();
  if (!Files.length) continue;
  const Bufs = Files.map((F) => fs.readFileSync(path.join(SessionDir, F)));
  const Solved = Solve(Bufs, Direction === 'c2s');
  Lines.push('== ' + Direction + '  消息 ' + Bufs.length + ' 条 ==');
  if (!Solved) {
    Lines.push('  未能解出（密钥不唯一或帧不完整）');
    Lines.push('');
    continue;
  }
  Lines.push('  明文前 ' + Solved.Start + ' 条，加密 ' + (Bufs.length - Solved.Start) + ' 条，K=' + Solved.K);
  // 时间线：每条帧相对该方向首条消息的时刻（毫秒），供 fake 模式按真实节奏回放
  const Times = ReadMessageTimes(SessionDir, Direction);
  if (!Times.length) Lines.push('  （无 log.txt 时间戳，时间线按 150ms 估算）');
  const Base = Times.length ? Times[0].Time : 0;
  const Timeline = [];
  Solved.Frames.forEach((Frame, I) => {
    const Name = Direction + '_' + String(I).padStart(4, '0') + '.bin';
    fs.writeFileSync(path.join(OutDir, Name), Frame.Buf);
    const Ms = Times[Frame.Msg] ? Math.max(0, Times[Frame.Msg].Time - Base) : I * 150;
    Timeline.push(Name + '\t' + Ms);
    Lines.push('  ' + Name + '  ' + String(Frame.Buf.length).padStart(6) + 'B  +' + Ms + 'ms  ' + Describe(Frame.Buf));
  });
  fs.writeFileSync(path.join(OutDir, 'timeline_' + Direction + '.txt'), Timeline.join('\n') + '\n', 'utf8');
  // 覆盖度自检：解出的帧必须覆盖到每一条 WS 消息，否则明确报出来（历史上这里静默丢过帧）
  const Covered = new Set(Solved.Frames.map((F) => F.Msg));
  if (Covered.size < Bufs.length) Lines.push('  ⚠ 只覆盖 ' + Covered.size + '/' + Bufs.length + ' 条消息，有帧没解出来');
  Lines.push('');
}

fs.writeFileSync(path.join(OutDir, 'summary.txt'), Lines.join('\n'), 'utf8');
console.log(Lines.join('\n'));
console.log('\n已写出明文帧: ' + OutDir);