// SPDX-License-Identifier: Apache-2.0
// SPDX-FileCopyrightText: Copyright contributors to the vLLM project

#include <Python.h>

#include <unistd.h>

#include <vector>

extern "C" {

static void _batch_lookup(const std::vector<const char*>& paths,
                          std::vector<int>& exists_flags) {
  for (size_t i = 0; i < paths.size(); i++) {
    exists_flags[i] = (access(paths[i], F_OK) == 0) ? 1 : 0;
  }
}

/// @brief Check file existence for a batch of paths.
/// @param paths list[str] – absolute paths to check.
/// @return list[bool] – True if the corresponding path exists, False otherwise.
/// @note Releases the GIL for the entire batch. File existence via access(2).
static PyObject* batch_lookup(PyObject* /*self*/, PyObject* args) {
  PyObject* path_list;
  if (!PyArg_ParseTuple(args, "O!", &PyList_Type, &path_list)) {
    return nullptr;
  }

  const Py_ssize_t n = PyList_Size(path_list);
  std::vector<const char*> paths(n);
  for (Py_ssize_t i = 0; i < n; i++) {
    paths[i] = PyUnicode_AsUTF8AndSize(PyList_GetItem(path_list, i), nullptr);
    if (paths[i] == nullptr) {
      return nullptr;
    }
  }

  std::vector<int> exists_flags(n);
  {
    Py_BEGIN_ALLOW_THREADS _batch_lookup(paths, exists_flags);
    Py_END_ALLOW_THREADS
  }

  PyObject* result = PyList_New(n);
  if (result == nullptr) {
    return nullptr;
  }
  for (Py_ssize_t i = 0; i < n; i++) {
    PyList_SetItem(result, i, PyBool_FromLong(exists_flags[i]));
  }
  return result;
}

static PyMethodDef fs_io_C_methods[] = {
    {"batch_lookup", batch_lookup, METH_VARARGS,
     "batch_lookup(paths: list[str]) -> list[bool]\n"
     "\n"
     "Check file existence for a batch of paths."},
    {nullptr, nullptr, 0, nullptr},
};

static struct PyModuleDef fs_io_C_module = {
    PyModuleDef_HEAD_INIT, "fs_io_C", "Filesystem helpers for KV offload", -1,
    fs_io_C_methods,
};

PyMODINIT_FUNC PyInit_fs_io_C(void) { return PyModule_Create(&fs_io_C_module); }

}  // extern "C"