/* ---------- PHP serialize 反序列化（字节精确，覆盖 s/i/d/b/a/N） ---------- */
export function phpUnserialize(input: string): unknown {
  const buf = Buffer.from(input, "utf8");
  let i = 0;
  function parse(): unknown {
    const type = String.fromCharCode(buf[i]);
    const colon = buf.indexOf(0x3a, i + 2); // 跳过 "类型:" 后定位计数值结束的冒号
    if (type === "N") { i += 2; return null; } // N;
    if (type === "b") { const v = buf[i + 2] === 0x31; i += 4; return v; } // b:0; / b:1;
    if (type === "i") { const j = buf.indexOf(0x3b, i); const v = parseInt(buf.toString("utf8", i + 2, j)); i = j + 1; return v; } // i:123;
    if (type === "d") { const j = buf.indexOf(0x3b, i); const v = parseFloat(buf.toString("utf8", i + 2, j)); i = j + 1; return v; } // d:1.5;
    if (type === "s") { // s:LEN:"...";（LEN 为 UTF-8 字节数）
      const len = parseInt(buf.toString("utf8", i + 2, colon));
      const start = colon + 2;
      const v = buf.toString("utf8", start, start + len);
      i = start + len + 2;
      return v;
    }
    if (type === "a") { // a:COUNT:{ key;value; ... }
      const n = parseInt(buf.toString("utf8", i + 2, colon));
      i = colon + 2; // 跳过 '{'
      const arr: unknown[] = [];
      const obj: Record<string, unknown> = {};
      let isArr = true;
      for (let k = 0; k < n; k++) {
        const key = parse();
        const val = parse();
        if (typeof key === "number") { isArr = isArr && true; arr[key] = val; }
        else { isArr = false; obj[String(key)] = val; }
      }
      i += 1; // 消费 '}'
      return isArr ? arr : obj;
    }
    throw new Error(`phpUnserialize: unknown type '${type}' at byte ${i}`);
  }
  return parse();
}