Mujoco_WASM/python/mujoco/structs.h

// Copyright 2022 DeepMind Technologies Limited
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef MUJOCO_PYTHON_STRUCTS_H_
#define MUJOCO_PYTHON_STRUCTS_H_

#include <array>
#include <istream>
#include <memory>
#include <optional>
#include <ostream>
#include <unordered_map>
#include <string>
#include <vector>

#include <absl/types/span.h>
#include <mujoco/mujoco.h>
#include <mujoco/mjxmacro.h>
#include "indexers.h"
#include "mjdata_meta.h"
#include "raw.h"
#include <pybind11/numpy.h>
#include <pybind11/pybind11.h>

namespace mujoco::python {
namespace _impl {
template <typename T>
class WrapperBase {
 public:
  WrapperBase(WrapperBase&& other) = default;

  T* get() { return ptr_; }
  const T* get() const { return ptr_; }

  const pybind11::handle owner() const { return owner_; }

 protected:
  static void DefaultCapsuleDestructor(PyObject* pyobj) {
    T* ptr = static_cast<T*>(PyCapsule_GetPointer(pyobj, nullptr));
    if (ptr) {
      delete ptr;
    }
  }

  // Takes ownership of ptr.
  explicit WrapperBase(T* ptr,
                       void (*destructor)(PyObject*) = DefaultCapsuleDestructor)
      : ptr_(ptr),
        owner_(pybind11::capsule(ptr_, /* name = */ nullptr, destructor)) {}

  // `ptr` is owned by `owner`.
  WrapperBase(T* ptr, pybind11::handle owner)
      : ptr_(ptr),
        owner_(pybind11::reinterpret_borrow<pybind11::object>(owner)) {}

  T* ptr_;
  pybind11::object owner_;
};

template <typename T, typename = void>
struct py_array_or_tuple {
  using type = pybind11::tuple;
};

template <typename T>
struct py_array_or_tuple<T, std::enable_if_t<std::is_arithmetic_v<T>>> {
  using type = pybind11::array_t<T>;
};

// A type that resolves to a NumPy array if the dtype is numeric, and
// a Python tuple otherwise.
template <typename T> using py_array_or_tuple_t =
    typename py_array_or_tuple<T>::type;

template <typename T>
struct enable_if_mj_struct {};

template <typename T>
class MjWrapper {};

template <typename T>
class StructListBase {
 public:
  StructListBase(T* ptr, int num, pybind11::handle owner) : ptr_(ptr) {
    for (int i = 0; i < num; ++i) {
      wrappers_.push_back(std::make_shared<MjWrapper<T>>(&ptr[i], owner));
    }
  }

  StructListBase(const StructListBase& other) = delete;
  StructListBase(StructListBase&& other) = default;

  MjWrapper<T>& operator[](int i) {
    if (i < 0 || i >= wrappers_.size()) {
      throw pybind11::index_error();
    }
    return *wrappers_[i];
  }

  int size() const {
    return wrappers_.size();
  }

 protected:
  // Slicing
  StructListBase(StructListBase& other, pybind11::slice slice) {
    pybind11::size_t start, stop, step, slicelength;
    slice.compute(other.size(), &start, &stop, &step, &slicelength);
    ptr_ = &other.ptr_[start];
    for (int i = start; i < stop; i += step) {
      wrappers_.push_back(other.wrappers_[i]);
    }
  }

  T* ptr_;

  // Using shared_ptr here so that we get identical Python objects when slicing.
  std::vector<std::shared_ptr<MjWrapper<T>>> wrappers_;
};

template <typename T>
struct is_mj_struct_list { static constexpr bool value = false; };

template <typename T>
class MjStructList {};

// ==================== MJOPTION ===============================================
template <>
class MjWrapper<raw::MjOption> : public WrapperBase<raw::MjOption> {
 public:
  MjWrapper();
  MjWrapper(const MjWrapper&);
  MjWrapper(MjWrapper&&) = default;
  MjWrapper(raw::MjOption* ptr, pybind11::handle owner);
  ~MjWrapper() = default;

  #define X(var, dim) py_array_or_tuple_t<mjtNum> var;
  MJOPTION_VECTORS
  #undef X
};

using MjOptionWrapper = MjWrapper<raw::MjOption>;

template <>
struct enable_if_mj_struct<raw::MjOption> { using type = void; };

// ==================== MJVISUAL ===============================================
template <>
class MjWrapper<raw::MjVisualHeadlight>
    : public WrapperBase<raw::MjVisualHeadlight> {
 public:
  MjWrapper();
  MjWrapper(const MjWrapper& other);
  MjWrapper(MjWrapper&&) = default;
  MjWrapper(raw::MjVisualHeadlight* ptr, pybind11::handle owner);
  ~MjWrapper() = default;

  #define X(var) py_array_or_tuple_t<float> var
  X(ambient);
  X(diffuse);
  X(specular);
  #undef X
};

using MjVisualHeadlightWrapper = MjWrapper<raw::MjVisualHeadlight>;

template <>
struct enable_if_mj_struct<raw::MjVisualHeadlight> { using type = void; };

template <>
class MjWrapper<raw::MjVisualRgba> : public WrapperBase<raw::MjVisualRgba> {
 public:
  MjWrapper();
  MjWrapper(const MjWrapper& other);
  MjWrapper(MjWrapper&&) = default;
  MjWrapper(raw::MjVisualRgba* ptr, pybind11::handle owner);
  ~MjWrapper() = default;

  #define X(var) py_array_or_tuple_t<float> var
  X(fog);
  X(haze);
  X(force);
  X(inertia);
  X(joint);
  X(actuator);
  X(actuatornegative);
  X(actuatorpositive);
  X(com);
  X(camera);
  X(light);
  X(selectpoint);
  X(connect);
  X(contactpoint);
  X(contactforce);
  X(contactfriction);
  X(contacttorque);
  X(contactgap);
  X(rangefinder);
  X(constraint);
  X(slidercrank);
  X(crankbroken);
  #undef X
};

using MjVisualRgbaWrapper = MjWrapper<raw::MjVisualRgba>;

template <>
struct enable_if_mj_struct<raw::MjVisualRgba> { using type = void; };

template <>
class MjWrapper<raw::MjVisual> : public WrapperBase<raw::MjVisual> {
 public:
  MjWrapper();
  MjWrapper(const MjWrapper& other);
  MjWrapper(MjWrapper&&) = default;
  MjWrapper(raw::MjVisual* ptr, pybind11::handle owner);
  ~MjWrapper() = default;

  MjVisualHeadlightWrapper headlight;
  MjVisualRgbaWrapper rgba;
};

using MjVisualWrapper = MjWrapper<raw::MjVisual>;

template <>
struct enable_if_mj_struct<raw::MjVisual> { using type = void; };

// ==================== MJSTATISTIC ============================================
template <>
class MjWrapper<raw::MjStatistic> : public WrapperBase<raw::MjStatistic> {
 public:
  MjWrapper();
  MjWrapper(const MjWrapper&);
  MjWrapper(MjWrapper&&) = default;
  MjWrapper(raw::MjStatistic* ptr, pybind11::handle owner);
  ~MjWrapper() = default;

  #define X(var) py_array_or_tuple_t<mjtNum> var
  X(center);
  #undef X
};

using MjStatisticWrapper = MjWrapper<raw::MjStatistic>;

template <>
struct enable_if_mj_struct<raw::MjStatistic> { using type = void; };

// ==================== MJWARNINGSTAT ==========================================
template <>
class MjWrapper<raw::MjWarningStat> : public WrapperBase<raw::MjWarningStat> {
 public:
  MjWrapper();
  MjWrapper(const MjWrapper&);
  MjWrapper(MjWrapper&&) = default;
  MjWrapper(raw::MjWarningStat* ptr, pybind11::handle owner);
  ~MjWrapper() = default;
};

using MjWarningStatWrapper = MjWrapper<raw::MjWarningStat>;

template <>
struct enable_if_mj_struct<raw::MjWarningStat> { using type = void; };

template <>
class MjStructList<raw::MjWarningStat>
    : public StructListBase<raw::MjWarningStat> {
 public:
  MjStructList(raw::MjWarningStat* ptr, int num, pybind11::handle owner);

  using StructListBase::operator[];
  using StructListBase::size;
  MjStructList Slice(pybind11::slice slice) {
    return MjStructList(*this, slice);
  }

#define X(type, var) pybind11::array_t<type> var
  X(int, lastinfo);
  X(int, number);
#undef X

 protected:
  MjStructList(MjStructList& other, pybind11::slice slice);
};

using MjWarningStatList = MjStructList<raw::MjWarningStat>;

template <>
struct py_array_or_tuple<raw::MjWarningStat> {
  using type = MjWarningStatList;
};

template <>
struct is_mj_struct_list<raw::MjWarningStat> {
  static constexpr bool value = true;
};

// ==================== MJTIMERSTAT ============================================
template <>
class MjWrapper<raw::MjTimerStat> : public WrapperBase<raw::MjTimerStat> {
 public:
  MjWrapper();
  MjWrapper(const MjWrapper&);
  MjWrapper(MjWrapper&&) = default;
  MjWrapper(raw::MjTimerStat* ptr, pybind11::handle owner);
  ~MjWrapper() = default;
};

using MjTimerStatWrapper = MjWrapper<raw::MjTimerStat>;

template <>
struct enable_if_mj_struct<raw::MjTimerStat> { using type = void; };

template <>
class MjStructList<raw::MjTimerStat> : public StructListBase<raw::MjTimerStat> {
 public:
  MjStructList(raw::MjTimerStat* ptr, int num, pybind11::handle owner);

  using StructListBase::operator[];
  using StructListBase::size;
  MjStructList Slice(pybind11::slice slice) {
    return MjStructList(*this, slice);
  }

#define X(type, var) pybind11::array_t<type> var
  X(mjtNum, duration);
  X(int, number);
#undef X

 protected:
  MjStructList(MjStructList& other, pybind11::slice slice);
};

using MjTimerStatList = MjStructList<raw::MjTimerStat>;

template <>
struct py_array_or_tuple<raw::MjTimerStat> {
  using type = MjTimerStatList;
};

template <>
struct is_mj_struct_list<raw::MjTimerStat> {
  static constexpr bool value = true;
};

// ==================== MJSOLVERSTAT ===========================================
template <>
class MjWrapper<raw::MjSolverStat> : public WrapperBase<raw::MjSolverStat> {
 public:
  MjWrapper();
  MjWrapper(const MjWrapper&);
  MjWrapper(MjWrapper&&) = default;
  MjWrapper(raw::MjSolverStat* ptr, pybind11::handle owner);
  ~MjWrapper() = default;
};

using MjSolverStatWrapper = MjWrapper<raw::MjSolverStat>;

template <>
struct enable_if_mj_struct<raw::MjSolverStat> { using type = void; };

template <>
class MjStructList<raw::MjSolverStat>
    : public StructListBase<raw::MjSolverStat> {
 public:
  MjStructList(raw::MjSolverStat* ptr, int num, pybind11::handle owner);

  using StructListBase::operator[];
  using StructListBase::size;
  MjStructList Slice(pybind11::slice slice) {
    return MjStructList(*this, slice);
  }

#define X(type, var) pybind11::array_t<type> var
  X(mjtNum, improvement);
  X(mjtNum, gradient);
  X(mjtNum, lineslope);
  X(int, nactive);
  X(int, nchange);
  X(int, neval);
  X(int, nupdate);
#undef X

 protected:
  MjStructList(MjStructList& other, pybind11::slice slice);
};

using MjSolverStatList = MjStructList<raw::MjSolverStat>;

template <>
struct py_array_or_tuple<raw::MjSolverStat> {
  using type = MjSolverStatList;
};

template <>
struct is_mj_struct_list<raw::MjSolverStat> {
  static constexpr bool value = true;
};

// ==================== MJMODEL ================================================
template <>
class MjWrapper<raw::MjModel> : public WrapperBase<raw::MjModel> {
 public:
  MjWrapper(const MjWrapper&);
  MjWrapper(MjWrapper&&);
  ~MjWrapper();

  MjModelIndexer& indexer() { return indexer_; }

  void Serialize(std::ostream& output) const;
  static MjWrapper<raw::MjModel> Deserialize(std::istream& input);

  static MjWrapper LoadXMLFile(
      const std::string& filename,
      const std::optional<
          std::unordered_map<std::string, pybind11::bytes>>& assets);

  static MjWrapper LoadBinaryFile(
      const std::string& filename,
      const std::optional<
          std::unordered_map<std::string, pybind11::bytes>>& assets);

  static MjWrapper LoadXML(
      const std::string& xml,
      const std::optional<
          std::unordered_map<std::string, pybind11::bytes>>& assets);

  static constexpr char kFromRawPointer[] =
      "__MUJOCO_STRUCTS_MJMODELWRAPPER_LOOKUP";
  static MjWrapper* FromRawPointer(raw::MjModel* m) noexcept;

  MjOptionWrapper opt;
  MjVisualWrapper vis;
  MjStatisticWrapper stat;

#define X(dtype, var, dim0, dim1) py_array_or_tuple_t<dtype> var;
  MJMODEL_POINTERS
#undef X
  // TODO(nimrod): Exclude text_data and names from the MJMODEL_POINTERS macro.
  pybind11::bytes text_data_bytes;
  pybind11::bytes names_bytes;

 private:
  explicit MjWrapper(raw::MjModel* ptr);

  MjModelIndexer indexer_;
};

using MjModelWrapper = MjWrapper<raw::MjModel>;

template <>
struct enable_if_mj_struct<raw::MjModel> { using type = void; };

// ==================== MJCONTACT ==============================================
template <>
class MjWrapper<raw::MjContact> : public WrapperBase<raw::MjContact> {
 public:
  MjWrapper();
  MjWrapper(const MjWrapper&);
  MjWrapper(MjWrapper&&) = default;
  MjWrapper(raw::MjContact* ptr, pybind11::handle owner);
  ~MjWrapper() = default;

  #define X(var) py_array_or_tuple_t<mjtNum> var
  X(pos);
  X(frame);
  X(friction);
  X(solref);
  X(solimp);
  X(H);
  #undef X
};

using MjContactWrapper = MjWrapper<raw::MjContact>;

template <>
struct enable_if_mj_struct<raw::MjContact> { using type = void; };

template <>
class MjStructList<raw::MjContact> : public StructListBase<raw::MjContact> {
 public:
  MjStructList(raw::MjContact* ptr, int num, pybind11::handle owner);

  using StructListBase::operator[];
  using StructListBase::size;
  MjStructList Slice(pybind11::slice slice) {
    return MjStructList(*this, slice);
  }

#define X(type, var) pybind11::array_t<type> var
  X(mjtNum, dist);
  X(mjtNum, pos);
  X(mjtNum, frame);
  X(mjtNum, includemargin);
  X(mjtNum, friction);
  X(mjtNum, solref);
  X(mjtNum, solimp);
  X(mjtNum, mu);
  X(mjtNum, H);
  X(int, dim);
  X(int, geom1);
  X(int, geom2);
  X(int, exclude);
  X(int, efc_address);
#undef X

 protected:
  MjStructList(MjStructList& other, pybind11::slice slice);
};

using MjContactList = MjStructList<raw::MjContact>;

template <>
struct py_array_or_tuple<raw::MjContact> {
  using type = MjContactList;
};

template <>
struct is_mj_struct_list<raw::MjContact> {
  static constexpr bool value = true;
};

// ==================== MJDATA =================================================
template <>
class MjWrapper<raw::MjData>: public WrapperBase<raw::MjData> {
 public:
  explicit MjWrapper(const MjModelWrapper& model);
  MjWrapper(const MjWrapper& other);
  MjWrapper(MjWrapper&&);
  ~MjWrapper();

  MjDataIndexer& indexer() { return indexer_; }

  void Serialize(std::ostream& output) const;
  static MjWrapper<raw::MjData> Deserialize(std::istream& input);

  static constexpr char kFromRawPointer[] =
      "__MUJOCO_STRUCTS_MJDATAWRAPPER_LOOKUP";
  static MjWrapper* FromRawPointer(raw::MjData* m) noexcept;

#define X(dtype, var, dim0, dim1) py_array_or_tuple_t<dtype> var;
  MJDATA_POINTERS
#undef X

  py_array_or_tuple_t<raw::MjWarningStat> warning;
  py_array_or_tuple_t<raw::MjTimerStat> timer;
  py_array_or_tuple_t<raw::MjSolverStat> solver;
  py_array_or_tuple_t<mjtNum> solver_fwdinv;
  py_array_or_tuple_t<mjtNum> energy;

 private:
  // Internal constructor which takes ownership of given mjData pointer.
  // Used for deserialization.
  explicit MjWrapper(MjDataMetadata&& metadata, raw::MjData* d);
  raw::MjData* Copy() const;

  MjDataMetadata metadata_;
  MjDataIndexer indexer_;
};

using MjDataWrapper = MjWrapper<raw::MjData>;

template <>
struct enable_if_mj_struct<raw::MjData> { using type = void; };

// ==================== MJVPERTURB =============================================
template <>
class MjWrapper<raw::MjvPerturb> : public WrapperBase<raw::MjvPerturb> {
 public:
  MjWrapper();
  MjWrapper(const MjWrapper&);
  MjWrapper(MjWrapper&&) = default;
  ~MjWrapper() = default;

  #define X(var) py_array_or_tuple_t<mjtNum> var
  X(refpos);
  X(refquat);
  X(localpos);
  #undef X
};

using MjvPerturbWrapper = MjWrapper<raw::MjvPerturb>;

template <>
struct enable_if_mj_struct<raw::MjvPerturb> { using type = void; };

// ==================== MJVCAMERA ==============================================
template <>
class MjWrapper<raw::MjvCamera> : public WrapperBase<raw::MjvCamera> {
 public:
  MjWrapper();
  MjWrapper(const MjWrapper&);
  MjWrapper(MjWrapper&&) = default;
  ~MjWrapper() = default;

  #define X(var) py_array_or_tuple_t<mjtNum> var
  X(lookat);
  #undef X
};

using MjvCameraWrapper = MjWrapper<raw::MjvCamera>;

template <>
struct enable_if_mj_struct<raw::MjvCamera> { using type = void; };

// ==================== MJVGLCAMERA ============================================
template <>
class MjWrapper<raw::MjvGLCamera> : public WrapperBase<raw::MjvGLCamera> {
 public:
  MjWrapper();
  MjWrapper(const MjWrapper&);
  MjWrapper(MjWrapper&&) = default;
  MjWrapper(raw::MjvGLCamera* ptr, pybind11::handle owner);
  explicit MjWrapper(raw::MjvGLCamera&& other);
  ~MjWrapper() = default;

  #define X(var) py_array_or_tuple_t<float> var
  X(pos);
  X(forward);
  X(up);
  #undef X
};

using MjvGLCameraWrapper = MjWrapper<raw::MjvGLCamera>;

template <>
struct enable_if_mj_struct<raw::MjvGLCamera> { using type = void; };

// ==================== MJVGEOM ================================================
template <>
class MjWrapper<raw::MjvGeom> : public WrapperBase<raw::MjvGeom> {
 public:
  MjWrapper();
  MjWrapper(const MjWrapper&);
  MjWrapper(MjWrapper&&) = default;
  MjWrapper(raw::MjvGeom* ptr, pybind11::handle owner);
  ~MjWrapper() = default;

  #define X(var) py_array_or_tuple_t<float> var
  X(texrepeat);
  X(size);
  X(pos);
  X(mat);
  X(rgba);
  #undef X
};

using MjvGeomWrapper = MjWrapper<raw::MjvGeom>;

template <>
struct enable_if_mj_struct<raw::MjvGeom> { using type = void; };

// ==================== MJVLIGHT ===============================================
template <>
class MjWrapper<raw::MjvLight> : public WrapperBase<raw::MjvLight> {
 public:
  MjWrapper();
  MjWrapper(const MjWrapper&);
  MjWrapper(MjWrapper&&) = default;
  MjWrapper(raw::MjvLight* ptr, pybind11::handle owner);
  ~MjWrapper() = default;

  #define X(var) py_array_or_tuple_t<float> var
  X(pos);
  X(dir);
  X(attenuation);
  X(ambient);
  X(diffuse);
  X(specular);
  #undef X
};

using MjvLightWrapper = MjWrapper<raw::MjvLight>;

template <>
struct enable_if_mj_struct<raw::MjvLight> { using type = void; };

// ==================== MJVOPTION ==============================================
template <>
class MjWrapper<raw::MjvOption> : public WrapperBase<raw::MjvOption> {
 public:
  MjWrapper();
  MjWrapper(const MjWrapper&);
  MjWrapper(MjWrapper&&) = default;
  ~MjWrapper() = default;

  #define X(var) py_array_or_tuple_t<mjtByte> var
  X(geomgroup);
  X(sitegroup);
  X(jointgroup);
  X(tendongroup);
  X(actuatorgroup);
  X(flags);
  #undef X
};

using MjvOptionWrapper = MjWrapper<raw::MjvOption>;

template <>
struct enable_if_mj_struct<raw::MjvOption> { using type = void; };

// ==================== MJVSCENE ===============================================
template <>
class MjWrapper<raw::MjvScene> : public WrapperBase<raw::MjvScene> {
 public:
  MjWrapper();
  MjWrapper(const MjWrapper&);
  MjWrapper(MjWrapper&&) = default;
  MjWrapper(const MjModelWrapper& model, int maxgeom);
  ~MjWrapper() = default;

  int nskinvert;

  #define X(dtype, var) py_array_or_tuple_t<dtype> var
  X(mjvGeom, geoms);
  X(int, geomorder);
  X(int, skinfacenum);
  X(int, skinvertadr);
  X(int, skinvertnum);
  X(float, skinvert);
  X(float, skinnormal);
  #undef X

  #define X(dtype, var) py_array_or_tuple_t<dtype> var
  X(raw::MjvLight, lights);
  X(raw::MjvGLCamera, camera);
  X(float, translate);
  X(float, rotate);
  X(mjtByte, flags);
  X(float, framergb);
  #undef X
};

using MjvSceneWrapper = MjWrapper<raw::MjvScene>;

template <>
struct enable_if_mj_struct<raw::MjvScene> { using type = void; };

// ==================== MJVFIGURE ==============================================
template <>
class MjWrapper<raw::MjvFigure> : public WrapperBase<raw::MjvFigure> {
 public:
  MjWrapper();
  MjWrapper(const MjWrapper&);
  MjWrapper(MjWrapper&&) = default;
  ~MjWrapper() = default;

  #define X(dtype, var) py_array_or_tuple_t<dtype> var
  X(int, flg_ticklabel);
  X(int, gridsize);
  X(float, gridrgb);
  X(float, figurergba);
  X(float, panergba);
  X(float, legendrgba);
  X(float, textrgb);
  X(float, linergb);
  X(float, range);
  X(int, highlight);
  X(int, linepnt);
  X(float, linedata);
  X(int, xaxispixel);
  X(int, yaxispixel);
  X(float, xaxisdata);
  X(float, yaxisdata);
  #undef X

  pybind11::array linename;
};

using MjvFigureWrapper = MjWrapper<raw::MjvFigure>;

template <>
struct enable_if_mj_struct<raw::MjvFigure> { using type = void; };
}  // namespace _impl

template <typename T>
using MjWrapper = typename std::conditional_t<
    std::is_const_v<T>, const _impl::MjWrapper<std::remove_const_t<T>>,
    _impl::MjWrapper<T>>;

template <typename T>
using enable_if_mj_struct_t =
    typename _impl::enable_if_mj_struct<std::remove_const_t<T>>::type;

using _impl::MjOptionWrapper;
using _impl::MjVisualHeadlightWrapper;
using _impl::MjVisualRgbaWrapper;
using _impl::MjVisualWrapper;
using _impl::MjStatisticWrapper;
using _impl::MjWarningStatWrapper;
using _impl::MjTimerStatWrapper;
using _impl::MjSolverStatWrapper;
using _impl::MjModelWrapper;
using _impl::MjDataWrapper;
using _impl::MjContactWrapper;
using _impl::MjvPerturbWrapper;
using _impl::MjvCameraWrapper;
using _impl::MjvGLCameraWrapper;
using _impl::MjvGeomWrapper;
using _impl::MjvLightWrapper;
using _impl::MjvOptionWrapper;
using _impl::MjvSceneWrapper;
using _impl::MjvFigureWrapper;

template <typename T>
using MjStructList = typename std::conditional_t<
    std::is_const_v<T>, const _impl::MjStructList<std::remove_const_t<T>>,
    _impl::MjStructList<T>>;

template <typename T>
static constexpr bool is_mj_struct_list_v =
    _impl::is_mj_struct_list<std::remove_const_t<T>>::value;

using _impl::MjContactList;
using _impl::MjWarningStatList;
using _impl::MjTimerStatList;
using _impl::MjSolverStatList;

// ==================== HELPER FUNCTIONS FOR BINDING ARRAYS ====================

// Python array initialization.
// If T is an arithmetic (i.e. numeric) type, returns a NumPy array that wraps
// around a preexisting data buffer.
template <typename T, typename Shape>
std::enable_if_t<std::is_arithmetic_v<T>, pybind11::array_t<T>>
static InitPyArray(Shape&& shape, T* buf, pybind11::handle owner) {
  int size = 1;
  for (const auto& i : shape) {
    size *= i;
  }
  if (shape.empty() || size == 0) {
    return pybind11::array_t<T>(shape);
  } else {
    return pybind11::array_t<T>(shape, buf, owner);
  }
}

// Same as above, but where we can determine array dimensions through the
// C array type directly.
template <typename T, typename Int, Int N>
std::enable_if_t<(N > 0) && std::is_arithmetic_v<T>, pybind11::array_t<T>>
static InitPyArray(T (&buf)[N], pybind11::handle owner) {
  return pybind11::array_t<T>({N}, &buf[0], owner);
}

template <typename T, typename Int, Int N1, Int N2>
std::enable_if_t<(N1*N2 > 0) && std::is_arithmetic_v<T>, pybind11::array_t<T>>
static InitPyArray(T (&buf)[N1][N2], pybind11::handle owner) {
  return pybind11::array_t<T>(
      {N1, N2}, &buf[0][0], owner);
}

template <typename T, typename Shape>
std::enable_if_t<is_mj_struct_list_v<T>, MjStructList<T>>
static InitPyArray(Shape&& shape, T* buf, pybind11::handle owner) {
  return MjStructList<T>(buf, shape[0], owner);
}

// For arrays of non-arithmetic type, we create tuple of tuples of MjWrapper<T>.
template <typename T, typename Shape>
std::enable_if_t<!std::is_arithmetic_v<T> && !is_mj_struct_list_v<T>,
                 pybind11::tuple>
static InitPyArray(Shape&& shape, T* buf, pybind11::handle owner) {
  int size = 1;
  for (const auto& i : shape) {
    size *= i;
  }
  if (shape.empty() || !size) {
    return pybind11::tuple();
  }

  pybind11::list out;
  const auto n = shape[0];
  if (shape.size() == 1) {
    for (int i = 0; i < n; ++i) {
      out.append(MjWrapper<T>(&buf[i], owner));
    }
  } else {
    auto block_shape = absl::MakeConstSpan(shape).subspan(1);
    auto block_size = std::accumulate(
        block_shape.begin(), block_shape.end(),
        1, std::multiplies<decltype(n)>());
    for (int i = 0; i < n; ++i) {
      out.append(InitPyArray(block_shape, &buf[i * block_size], owner));
    }
  }
  return std::move(out);
}

// Same as above, but where we can determine array dimensions through the
// C array type directly.
template <typename T, typename Int, Int N>
std::enable_if_t<(N > 0) && !std::is_arithmetic_v<T> &&
                 !std::is_array_v<T> && !is_mj_struct_list_v<T>,
                 pybind11::tuple>
static InitPyArray(T (&buf)[N], pybind11::handle owner) {
  return InitPyArray(std::array{N}, buf, owner);
}

template <typename T, typename Int, Int N1, Int N2>
std::enable_if_t<(N1*N2 > 0) && !std::is_arithmetic_v<T> &&
                 !std::is_array_v<T> && !is_mj_struct_list_v<T>,
                 pybind11::tuple>
static InitPyArray(T (&buf)[N1][N2], pybind11::handle owner) {
  return InitPyArray(std::array{N1, N2}, buf, owner);
}

template <typename T, typename Int, Int N>
std::enable_if_t<is_mj_struct_list_v<T>, MjStructList<T>>
static InitPyArray(T (&buf)[N], pybind11::handle owner) {
  return MjStructList<T>(buf, N, owner);
}

// Helpers for defining array/tuple properties in pybind11 classes.
//
// Defines a NumPy array property of a Python class that supports assignments.
// Specifically, we implement the setter such that `obj.arr = val` is the same
// as `obj.arr[:] = val`.
//
// Use `DefinePyArray(c, "somearray", &MjStructHolder<C>::somearray)`
// as a drop-in replacement for
// `c.def_readonly("somearray", &MjStructHolder<C>::somearray)`.
template <typename T, typename C, typename... O>
static void DefinePyArray(pybind11::class_<C, O...> c, const char* name,
                          pybind11::array_t<T> C::* arr) {
  namespace py = pybind11;
  c.def_property(
      name,
      [arr](const C& wrapper) { return wrapper.*arr; },
      [arr](const C& wrapper, py::handle rhs) -> void {
        (wrapper.*arr)[py::slice(py::none(), py::none(), py::none())] = rhs;
      }
  );
}

// For array of non-arithmetic type, we bind to tuples rather than NumPy array.
// These can't be assigned to directly so we just use def_readonly.
template <typename T, typename C, typename... O>
static void DefinePyArray(pybind11::class_<C, O...> c, const char* name,
                          T C::* arr) {
  c.def_property_readonly(
      name,
      [arr](const C& wrapper) -> auto& { return wrapper.*arr; });
}

template <typename Raw, int N, typename C, typename... O>
static void DefinePyStr(pybind11::class_<C, O...> c, const char* name,
                        char (Raw::* arr)[N]) {
  c.def_property(
      name,
      [arr](const C& c) { return pybind11::str(c.get()->*arr); },
      [name = std::string(name), arr](C& c, std::string_view rhs) {
        constexpr int kMaxLen = sizeof(c.get()->*arr);
        const int actual_len = rhs.size();
        if (actual_len >= kMaxLen) {
          std::ostringstream msg;
          msg << "len(" << name << ") cannot exceed " << kMaxLen - 1
              << ": got length " << actual_len;
          throw pybind11::value_error(msg.str());
        }
        rhs.copy(c.get()->*arr, actual_len);
        (c.get()->*arr)[actual_len] = '\0';
      });
}

}  // namespace mujoco::python

#endif  // MUJOCO_PYTHON_STRUCTS_H_