/**
 * engines/cpp/main.cpp
 * --------------------
 * C++ 动力学模拟引擎（模板/参考实现）。
 *
 * 接口与 C 引擎一致：
 *   输入: param.json, <input_dir>/coord.txt, connection.txt, bond.txt
 *   输出: <output_dir>/trajectory.txt (JSON)
 *
 * 编译:
 *   g++ -O3 -march=native -o build/dynamics_cpp main.cpp
 *
 * 用法:
 *   ./build/dynamics_cpp <input_dir> <output_dir> <param_json>
 */

#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <vector>
#include <cmath>
#include <chrono>
#include <cstring>

struct SimParams {
    double box_a;
    int NT;
    double DT;
    int NSTEP;
    int warmup_steps;
    double G[3];
    double B[3];
};

struct Atom {
    int id;
    double mass, radius;
    double x, y, z;
    double vx, vy, vz;
    bool fx, fy, fz;  // fixed constraints
};

struct Bond {
    int i, j;
    double stiffness, rest_length;
};

// ========================================================================
// 请在下方实现 Leapfrog 算法
// 参考 engines/c/main.c 中的物理核心实现
// ========================================================================

int main(int argc, char **argv) {
    if (argc < 4) {
        std::cerr << "用法: " << argv[0] << " <input_dir> <output_dir> <param_json>" << std::endl;
        return 1;
    }

    std::string input_dir  = argv[1];
    std::string output_dir = argv[2];
    std::string param_path = argv[3];

    auto t0 = std::chrono::high_resolution_clock::now();

    // TODO: 读取 param.json、coord.txt、connection.txt、bond.txt
    // TODO: 执行 Leapfrog 模拟
    // TODO: 输出 trajectory.txt (JSON 格式)
    //
    // 提示：输出格式与 Python 版兼容，参考 engines/c/main.c 中的 write_trajectory_json

    auto t1 = std::chrono::high_resolution_clock::now();
    double elapsed = std::chrono::duration<double>(t1 - t0).count();

    std::cout << "[C++-engine] 占位: NT=" << 0 << ", " << elapsed << " s (待实现)" << std::endl;
    return 0;
}