// 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;
}

module.exports = { extractZip };