// zip.js —— 零依赖 ZIP 解压（stored/deflate），供技能安装与热更新复用。
"use strict";
const fs = require("fs");
const path = require("path");
const zlib = require("zlib");

// 解析中央目录，把 zip 内容写入 destDir；返回写出的文件数。
function extractZip(buf, destDir) {
  // 找 EOCD（0x06054b50），从尾部回扫
  let eocd = -1;
  for (let i = buf.length - 22; i >= 0 && i >= buf.length - 22 - 65536; i--) {
    if (buf.readUInt32LE(i) === 0x06054b50) { eocd = i; break; }
  }
  if (eocd < 0) throw new Error("不是有效的 zip（找不到 EOCD）");
  const count = buf.readUInt16LE(eocd + 10);
  let ptr = buf.readUInt32LE(eocd + 16); // 中央目录起始偏移
  let written = 0;
  for (let n = 0; n < count; n++) {
    if (buf.readUInt32LE(ptr) !== 0x02014b50) break;
    const method = buf.readUInt16LE(ptr + 10);
    const compSize = buf.readUInt32LE(ptr + 20);
    const nameLen = buf.readUInt16LE(ptr + 28);
    const extraLen = buf.readUInt16LE(ptr + 30);
    const commentLen = buf.readUInt16LE(ptr + 32);
    const localOff = buf.readUInt32LE(ptr + 42);
    const name = buf.toString("utf8", ptr + 46, ptr + 46 + nameLen);
    ptr += 46 + nameLen + extraLen + commentLen;
    // 读本地头，定位数据
    if (buf.readUInt32LE(localOff) !== 0x04034b50) continue;
    const lNameLen = buf.readUInt16LE(localOff + 26);
    const lExtraLen = buf.readUInt16LE(localOff + 28);
    const dataStart = localOff + 30 + lNameLen + lExtraLen;
    const comp = buf.subarray(dataStart, dataStart + compSize);
    // 防目录穿越
    const safe = name.replace(/\\/g, "/").replace(/^\/+/, "");
    if (safe.includes("../")) continue;
    const outPath = path.join(destDir, safe);
    if (safe.endsWith("/")) { fs.mkdirSync(outPath, { recursive: true }); continue; }
    fs.mkdirSync(path.dirname(outPath), { recursive: true });
    let data;
    if (method === 0) data = comp;
    else if (method === 8) data = zlib.inflateRawSync(comp);
    else throw new Error(`不支持的压缩方式 ${method}`);
    fs.writeFileSync(outPath, data);
    written++;
  }
  return written;
}

// ---- 零依赖 ZIP 压缩（deflate/stored），供员工团队打包等复用 ----
// CRC32 表（懒加载）
let CRC_TABLE = null;
function crc32(buf) {
  if (!CRC_TABLE) {
    CRC_TABLE = new Int32Array(256);
    for (let n = 0; n < 256; n++) {
      let c = n;
      for (let k = 0; k < 8; k++) c = c & 1 ? 0xedb88320 ^ (c >>> 1) : c >>> 1;
      CRC_TABLE[n] = c;
    }
  }
  let crc = ~0;
  for (let i = 0; i < buf.length; i++) crc = (crc >>> 8) ^ CRC_TABLE[(crc ^ buf[i]) & 0xff];
  return (~crc) >>> 0;
}

// MS-DOS 时间/日期（固定用一个合法值即可，不追求精确时间戳）
function dosDateTime(d) {
  const date = d || new Date();
  const time = ((date.getHours() & 0x1f) << 11) | ((date.getMinutes() & 0x3f) << 5) | ((date.getSeconds() / 2) & 0x1f);
  const day = (((date.getFullYear() - 1980) & 0x7f) << 9) | (((date.getMonth() + 1) & 0x0f) << 5) | (date.getDate() & 0x1f);
  return { time: time & 0xffff, date: day & 0xffff };
}

// files: [{ path, content(string|Buffer), mode?(unix 权限，如 0o755) }]
// 返回一个 zip 的 Buffer。目录靠文件路径里的 "/" 隐含，无需单独目录项。
function createZip(files) {
  const { time, date } = dosDateTime();
  const locals = [];
  const centrals = [];
  let offset = 0;
  for (const f of files) {
    const nameBuf = Buffer.from(String(f.path).replace(/^\/+/, ""), "utf8");
    const raw = Buffer.isBuffer(f.content) ? f.content : Buffer.from(String(f.content == null ? "" : f.content), "utf8");
    const crc = crc32(raw);
    // 尝试 deflate；若压不小就存储（method 0）
    let method = 8;
    let comp = zlib.deflateRawSync(raw, { level: 9 });
    if (comp.length >= raw.length) { method = 0; comp = raw; }

    // 本地文件头
    const lh = Buffer.alloc(30);
    lh.writeUInt32LE(0x04034b50, 0);
    lh.writeUInt16LE(20, 4);            // version needed
    lh.writeUInt16LE(0, 6);             // flags
    lh.writeUInt16LE(method, 8);
    lh.writeUInt16LE(time, 10);
    lh.writeUInt16LE(date, 12);
    lh.writeUInt32LE(crc, 14);
    lh.writeUInt32LE(comp.length, 18);
    lh.writeUInt32LE(raw.length, 22);
    lh.writeUInt16LE(nameBuf.length, 26);
    lh.writeUInt16LE(0, 28);           // extra len
    locals.push(lh, nameBuf, comp);

    // 中央目录项
    const ch = Buffer.alloc(46);
    // unix 权限写进外部属性高 16 位（低位保留），默认 0644，可执行给 0755
    const unixMode = f.mode ? f.mode : 0o644;
    const externalAttr = (unixMode << 16) >>> 0;
    ch.writeUInt32LE(0x02014b50, 0);
    ch.writeUInt16LE(0x031e, 4);       // version made by (unix)
    ch.writeUInt16LE(20, 6);           // version needed
    ch.writeUInt16LE(0, 8);            // flags
    ch.writeUInt16LE(method, 10);
    ch.writeUInt16LE(time, 12);
    ch.writeUInt16LE(date, 14);
    ch.writeUInt32LE(crc, 16);
    ch.writeUInt32LE(comp.length, 20);
    ch.writeUInt32LE(raw.length, 24);
    ch.writeUInt16LE(nameBuf.length, 28);
    ch.writeUInt16LE(0, 30);           // extra len
    ch.writeUInt16LE(0, 32);           // comment len
    ch.writeUInt16LE(0, 34);           // disk number
    ch.writeUInt16LE(0, 36);           // internal attr
    ch.writeUInt32LE(externalAttr, 38);
    ch.writeUInt32LE(offset, 42);
    centrals.push(ch, nameBuf);

    offset += lh.length + nameBuf.length + comp.length;
  }

  const localPart = Buffer.concat(locals);
  const centralPart = Buffer.concat(centrals);
  const eocd = Buffer.alloc(22);
  eocd.writeUInt32LE(0x06054b50, 0);
  eocd.writeUInt16LE(0, 4);
  eocd.writeUInt16LE(0, 6);
  eocd.writeUInt16LE(files.length, 8);
  eocd.writeUInt16LE(files.length, 10);
  eocd.writeUInt32LE(centralPart.length, 12);
  eocd.writeUInt32LE(localPart.length, 16); // central dir offset
  eocd.writeUInt16LE(0, 20);
  return Buffer.concat([localPart, centralPart, eocd]);
}

module.exports = { extractZip, createZip };