// Copyright 2021 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.

// Tests for user/user_objects.cc.

#include <array>
#include <cstddef>
#include <string>
#include <vector>

#include <gmock/gmock.h>
#include <gtest/gtest.h>
#include <absl/strings/str_format.h>
#include <mujoco/mjmodel.h>
#include <mujoco/mjtnum.h>
#include <mujoco/mujoco.h>
#include "src/cc/array_safety.h"
#include "test/fixture.h"

namespace mujoco {
namespace {

using MjCMeshTest = MujocoTest;

static const char* const kMeshPath =
    "user/testdata/mesh.xml";
static const char* const kDuplicateVerticesPath =
    "user/testdata/duplicate_vertices.xml";
static const char* const kCubePath =
    "user/testdata/cube.xml";
static const char* const kTorusPath =
    "user/testdata/torus.xml";
static const char* const kTorusShellPath =
    "user/testdata/torus_shell.xml";
static const char* const kConvexInertiaPath =
    "user/testdata/inertia_convex.xml";
static const char* const kConcaveInertiaPath =
    "user/testdata/inertia_concave.xml";
static const char* const kShellInertiaPath =
    "user/testdata/inertia_shell.xml";
static const char* const kTorusQuadsPath =
    "user/testdata/torus_quads.xml";
static const char* const kTexturedTorusPath =
    "user/testdata/textured_torus.xml";
static const char* const kDuplicateOBJPath =
    "user/testdata/duplicate.xml";
static const char* const kMalformedFaceOBJPath =
    "user/testdata/malformed_face.xml";

using ::testing::HasSubstr;
using ::testing::IsNull;

// ------------- test invalid filenames ----------------------------------------

TEST_F(MjCMeshTest, UnknownMeshFormat) {
  static constexpr char xml_format[] = R"(
    <mujoco>
      <asset>
        <mesh name="m" file="%s"/>
      </asset>
      <worldbody>
        <geom type="mesh" mesh="m"/>
      </worldbody>
    </mujoco>
  )";
  std::vector<std::string> invalid_names = {
    "noextension",
    "anobj",
    "f",
    "mesh.exe",
    "file%s"
  };
  for (const auto& name : invalid_names) {
    std::string xml = absl::StrFormat(xml_format, name);
    std::array<char, 1024> error;
    mjModel* model =
        LoadModelFromString(xml.c_str(), error.data(), error.size());
    ASSERT_THAT(model, testing::IsNull())
        << "Should fail to load a mesh named: " << name;
    EXPECT_THAT(error.data(), HasSubstr("Unknown mesh file type"));
    EXPECT_THAT(error.data(), HasSubstr(name));
  }
}

// -------------------- test OS filesystem fallback ----------------------------

TEST_F(MjCMeshTest, LoadMSHWithVFS) {
  static constexpr char xml[] = R"(
  <mujoco>
    <asset>
      <mesh name="mesh1" file="unknown_file.msh"/>
    </asset>
    <worldbody>
      <geom type="mesh" mesh="mesh1"/>
    </worldbody>
  </mujoco>
  )";

  char error[1024];
  size_t error_sz = 1024;

  // load VFS on the heap
  auto vfs = std::make_unique<mjVFS>();
  mj_defaultVFS(vfs.get());

  // should fallback to OS filesystem
  mjModel* model = LoadModelFromString(xml, error, error_sz, vfs.get());
  EXPECT_THAT(model, IsNull());
  EXPECT_THAT(error, HasSubstr("resource not found via provider or OS filesystem"));
}

TEST_F(MjCMeshTest, LoadOBJWithVFS) {
  static constexpr char xml[] = R"(
  <mujoco>
    <asset>
      <mesh name="mesh1" file="unknown_file.obj"/>
    </asset>
    <worldbody>
      <geom type="mesh" mesh="mesh1"/>
    </worldbody>
  </mujoco>
  )";

  char error[1024];
  size_t error_sz = 1024;

  // load VFS on the heap
  auto vfs = std::make_unique<mjVFS>();
  mj_defaultVFS(vfs.get());

  // should fallback to OS filesystem
  mjModel* model = LoadModelFromString(xml, error, error_sz, vfs.get());
  EXPECT_THAT(model, IsNull());
  EXPECT_THAT(error, HasSubstr("resource not found via provider or OS filesystem"));
}

TEST_F(MjCMeshTest, LoadSTLWithVFS) {
  static constexpr char xml[] = R"(
  <mujoco>
    <asset>
      <mesh name="mesh1" file="unknown_file.stl"/>
    </asset>
    <worldbody>
      <geom type="mesh" mesh="mesh1"/>
    </worldbody>
  </mujoco>
  )";

  char error[1024];
  size_t error_sz = 1024;

  // load VFS on the heap
  auto vfs = std::make_unique<mjVFS>();
  mj_defaultVFS(vfs.get());

  // should fallback to OS filesystem
  mjModel* model = LoadModelFromString(xml, error, error_sz, vfs.get());
  EXPECT_THAT(model, IsNull());
  EXPECT_THAT(error, HasSubstr("resource not found via provider or OS filesystem"));
}

// ------------- test vertex de-duplication (STL) ------------------------------

TEST_F(MjCMeshTest, DeDuplicateSTLVertices) {
  const std::string xml_path = GetTestDataFilePath(kDuplicateVerticesPath);
  char error[1024];
  size_t error_sz = 1024;
  mjModel* model = mj_loadXML(xml_path.c_str(), 0, error, error_sz);
  ASSERT_EQ(model->nmeshvert, 4);
  mj_deleteModel(model);
}

// -------------------- test Mesh loading (MSH) --------------------------------

TEST_F(MjCMeshTest, LoadMSH) {
  const std::string xml_path = GetTestDataFilePath(kMeshPath);
  char error[1024];
  size_t error_sz = 1024;
  mjModel* model = mj_loadXML(xml_path.c_str(), 0, error, error_sz);
  ASSERT_THAT(model, testing::NotNull()) << error;
  ASSERT_EQ(model->nmeshvert, 36);
  mj_deleteModel(model);
}

// ------------- test OBJ loading ----------------------------------------------

using MjCMeshTest = MujocoTest;

TEST_F(MjCMeshTest, LoadCube) {
  const std::string xml_path = GetTestDataFilePath(kCubePath);
  mjModel* model = mj_loadXML(xml_path.c_str(), 0, nullptr, 0);
  ASSERT_GT(model->ngeom, 0);
  ASSERT_EQ(model->nmeshvert, 8);
  ASSERT_EQ(model->nmeshface, 12);
  mj_deleteModel(model);
}

TEST_F(MjCMeshTest, LoadTorus) {
  const std::string xml_path = GetTestDataFilePath(kTorusPath);
  std::array<char, 1024> error;
  mjModel* model = mj_loadXML(xml_path.c_str(), 0, error.data(), error.size());
  ASSERT_GT(model->ngeom, 0);
  ASSERT_GT(model->nmeshvert, 0);
  mj_deleteModel(model);
}

TEST_F(MjCMeshTest, LoadTorusQuads) {
  const std::string xml_path = GetTestDataFilePath(kTorusQuadsPath);
  std::array<char, 1024> error;
  mjModel* model = mj_loadXML(xml_path.c_str(), 0, error.data(), error.size());
  ASSERT_GT(model->ngeom, 0);
  ASSERT_GT(model->nmeshvert, 0);
  mj_deleteModel(model);
}

TEST_F(MjCMeshTest, LoadTexturedTorus) {
  const std::string xml_path = GetTestDataFilePath(kTexturedTorusPath);
  std::array<char, 1024> error;
  mjModel* model = mj_loadXML(xml_path.c_str(), 0, error.data(), error.size());
  ASSERT_GT(model->ngeom, 0);
  ASSERT_GT(model->nmeshvert, 0);
  ASSERT_GT(model->ntex, 0);
  ASSERT_GT(model->ntexdata, 0);
  mj_deleteModel(model);
}

TEST_F(MjCMeshTest, KeepDuplicateOBJVertices) {
  const std::string xml_path = GetTestDataFilePath(kDuplicateOBJPath);
  char error[1024];
  size_t error_sz = 1024;
  mjModel* model = mj_loadXML(xml_path.c_str(), 0, error, error_sz);
  ASSERT_EQ(model->nmeshvert, 16);
  mj_deleteModel(model);
}

TEST_F(MjCMeshTest, SaveMeshOnce) {
  const std::string xml_path = GetTestDataFilePath(kCubePath);
  std::array<char, 1024> error;
  mjModel* model = mj_loadXML(xml_path.c_str(), 0, error.data(), error.size());
  std::string saved_xml = SaveAndReadXml(model);
  EXPECT_THAT(saved_xml, Not(testing::HasSubstr("vertex")));
  mj_deleteModel(model);
}

TEST_F(MjCMeshTest, TinyMeshLoads) {
  static constexpr char xml[] = R"(
  <mujoco>
    <asset>
      <mesh name="tiny" vertex="0 0 0  1e-4 0 0  0 1e-4 0  0 0 1e-4"/>
    </asset>
    <worldbody>
      <geom type="mesh" mesh="tiny"/>
    </worldbody>
  </mujoco>
  )";
  mjModel* model = LoadModelFromString(xml);
  ASSERT_THAT(model, testing::NotNull());
  mj_deleteModel(model);
}

// ------------- test inline loading ------------------------------------------
TEST_F(MjCMeshTest, FaceNormalAutogenerated) {
  static constexpr char xml[] = R"(
  <mujoco>
    <asset>
      <mesh name="example_mesh"
        vertex="0 0 0  1 0 0  0 1 0  0 0 1"
        normal="1 0 0  0 1 0  0 0 1  0.707 0 0.707"
        face="0 2 1  0 3 2" />
    </asset>
    <worldbody>
      <geom type="mesh" mesh="example_mesh"/>
    </worldbody>
  </mujoco>
  )";
  mjModel* model = LoadModelFromString(xml);
  ASSERT_THAT(model, testing::NotNull());
  mj_deleteModel(model);
}

// ------------- test inertia -------------------------------------------------

TEST_F(MjCMeshTest, SmallInertiaLoads) {
  static constexpr char xml[] = R"(
  <mujoco>
    <asset>
      <mesh name="tiny" vertex="0 0 0  1e-4 0 0  0 1e-4 0  0 0 1e-4"/>
    </asset>
    <worldbody>
      <body>
        <freejoint/>
        <geom type="mesh" mesh="tiny"/>
        <geom name="small" size=".001"/>
      </body>
    </worldbody>
  </mujoco>
  )";
  mjModel* model = LoadModelFromString(xml);
  ASSERT_THAT(model, testing::NotNull());
  mj_deleteModel(model);
}

TEST_F(MjCMeshTest, TinyInertiaFails) {
  static constexpr char xml[] = R"(
  <mujoco>
    <asset>
      <mesh name="tiny" vertex="0 0 0  1e-4 0 0  0 1e-4 0  0 0 1e-4"/>
    </asset>
    <worldbody>
      <body>
        <freejoint/>
        <geom type="mesh" mesh="tiny"/>
      </body>
    </worldbody>
  </mujoco>
  )";
  std::array<char, 1024> error;
  LoadModelFromString(xml, error.data(), error.size());
  EXPECT_THAT(
      error.data(),
      HasSubstr(
          "mass and inertia of moving bodies must be larger than mjMINVAL"));
}

TEST_F(MjCMeshTest, MalformedFaceFails) {
  const std::string xml_path = GetTestDataFilePath(kMalformedFaceOBJPath);
  std::array<char, 1024> error;
  mjModel* model = mj_loadXML(xml_path.c_str(), 0, error.data(), error.size());
  EXPECT_THAT(model, testing::IsNull());
  EXPECT_THAT(error.data(), HasSubstr(
        "Error: faces of mesh 'malformed_face' have inconsistent orientation. "
        "Please check the faces containing the vertices 1 and 2."));
}

TEST_F(MjCMeshTest, FlippedFaceFails) {
  static constexpr char xml[] = R"(
  <mujoco>
    <asset>
      <mesh name="example_mesh"
        vertex="0 0 0  1 0 0  0 1 0  0 0 1"
        face="2 0 3  0 1 3  1 2 3  0 1 2" />
    </asset>
    <worldbody>
      <body>
        <geom type="mesh" mesh="example_mesh"/>
      </body>
    </worldbody>
  </mujoco>
  )";
  std::array<char, 1024> error;
  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
  EXPECT_THAT(model, testing::IsNull());
  EXPECT_THAT(error.data(), HasSubstr(
        "Error: faces of mesh 'example_mesh' have inconsistent orientation. "
        "Please check the faces containing the vertices 1 and 2."));
}

void CheckTetrahedronWasRescaled(mjModel* model) {
  // The rotated and rescaled positions of the tetrahedron
  // with vertices (0, 0, 0), (1, 0, 0), (0, 2, 0), (0, 0, 3)
  // after mesh preprocessing is performed
  std::vector<mjtNum> vert = {
    -0.51610732078552246,  -0.57402724027633667, -0.5283237099647522,
     0.42337465286254883,  -0.90627568960189819, -0.61189728975296021,
     0.065528042614459991,  1.2306677103042603,  -1.1645441055297852,
     0.027204651385545731,  0.24963514506816864,  2.3047652244567871};
  mjtNum tolerance = std::numeric_limits<float>::epsilon();
  for (int i=0; i < 12; ++i) {
    EXPECT_NEAR(model->mesh_vert[i], vert[i], tolerance);
  }
}

TEST_F(MjCMeshTest, FlippedFaceAllowedWorld) {
  static constexpr char xml[] = R"(
  <mujoco>
    <asset>
      <mesh name="example_mesh"
        vertex="0 0 0  1 0 0  0 2 0  0 0 3"
        face="2 0 3  0 1 3  1 2 3  0 1 2" />
    </asset>
    <worldbody>
      <geom type="mesh" mesh="example_mesh"/>
    </worldbody>
  </mujoco>
  )";
  std::array<char, 1024> error;
  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
  EXPECT_THAT(model, testing::NotNull());
  CheckTetrahedronWasRescaled(model);
  mj_deleteModel(model);
}

TEST_F(MjCMeshTest, FlippedFaceAllowedNoMass) {
  static constexpr char xml[] = R"(
  <mujoco>
    <asset>
      <mesh name="example_mesh"
        vertex="0 0 0  1 0 0  0 2 0  0 0 3"
        face="2 0 3  0 1 3  1 2 3  0 1 2" />
    </asset>
    <worldbody>
      <body>
        <geom type="mesh" mesh="example_mesh" mass="0"/>
      </body>
    </worldbody>
  </mujoco>
  )";
  std::array<char, 1024> error;
  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
  EXPECT_THAT(model, testing::NotNull());
  CheckTetrahedronWasRescaled(model);
  mj_deleteModel(model);
}

TEST_F(MjCMeshTest, FlippedFaceAllowedInertial) {
  static constexpr char xml[] = R"(
  <mujoco>
    <asset>
      <mesh name="example_mesh"
        vertex="0 0 0  1 0 0  0 2 0  0 0 3"
        face="2 0 3  0 1 3  1 2 3  0 1 2" />
    </asset>
    <worldbody>
      <body>
        <inertial pos="0 0 0" mass="1"/>
        <geom type="mesh" mesh="example_mesh"/>
      </body>
    </worldbody>
  </mujoco>
  )";
  std::array<char, 1024> error;
  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
  EXPECT_THAT(model, testing::NotNull());
  CheckTetrahedronWasRescaled(model);
  mj_deleteModel(model);
}

TEST_F(MjCMeshTest, FlippedFaceAllowedNegligibleArea) {
  static constexpr char xml[] = R"(
  <mujoco>
    <asset>
      <mesh name="example_mesh"
        vertex="0 0 0  1 0 0  0 2 0  0 0 3  0 0 3"
        face="2 0 3  0 1 3  1 2 3  0 2 1  0 3 4" />
    </asset>
    <worldbody>
      <body>
        <geom type="mesh" mesh="example_mesh"/>
      </body>
    </worldbody>
  </mujoco>
  )";
  std::array<char, 1024> error;
  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
  EXPECT_THAT(model, testing::NotNull());
  CheckTetrahedronWasRescaled(model);
  mj_deleteModel(model);
}

TEST_F(MjCMeshTest, ShellUsesVolumeFrame) {
  const std::string xml_path_v = GetTestDataFilePath(kTorusPath);
  const std::string xml_path_s = GetTestDataFilePath(kTorusShellPath);
  std::array<char, 1024> error;
  mjModel* mv = mj_loadXML(xml_path_v.c_str(), 0, error.data(), error.size());
  mjModel* ms = mj_loadXML(xml_path_s.c_str(), 0, error.data(), error.size());
  mjtNum tolerance = std::numeric_limits<float>::epsilon();
  EXPECT_NEAR(mv->geom_quat[0], ms->geom_quat[0], tolerance);
  EXPECT_NEAR(mv->geom_quat[1], ms->geom_quat[1], tolerance);
  EXPECT_NEAR(mv->geom_quat[2], ms->geom_quat[2], tolerance);
  EXPECT_NEAR(mv->geom_quat[3], ms->geom_quat[3], tolerance);
  mj_deleteModel(mv);
  mj_deleteModel(ms);
}

TEST_F(MjCMeshTest, AreaTooSmall) {
  static constexpr char xml[] = R"(
  <mujoco>
    <asset>
      <mesh name="example_mesh"
        vertex="0 0 0  1e-8 0 0  0 1e-8 0  0 0 1e-8"
        face="2 0 3  0 1 3  1 2 3  0 2 1" />
    </asset>
    <worldbody>
      <body>
        <geom type="mesh" mesh="example_mesh" shellinertia="true"/>
      </body>
    </worldbody>
  </mujoco>
  )";
  std::array<char, 1024> error;
  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
  EXPECT_THAT(model, testing::IsNull());
  EXPECT_THAT(error.data(), HasSubstr("mesh surface area is too small"));
}

TEST_F(MjCMeshTest, AreaTooSmallAllowedWorld) {
  static constexpr char xml[] = R"(
  <mujoco>
    <asset>
      <mesh name="example_mesh"
        vertex="0 0 0  1e-8 0 0  0 1e-8 0  0 0 1e-8"
        face="2 0 3  0 1 3  1 2 3  0 2 1" />
    </asset>
    <worldbody>
      <geom type="mesh" mesh="example_mesh"/>
    </worldbody>
  </mujoco>
  )";
  std::array<char, 1024> error;
  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
  EXPECT_THAT(model, testing::NotNull());
  mj_deleteModel(model);
}

TEST_F(MjCMeshTest, VolumeTooSmall) {
  static constexpr char xml[] = R"(
  <mujoco>
    <asset>
      <mesh name="example_mesh"
        vertex="0 0 0  1 0 0  0 1 0  0 0 1"
        face="0 2 1" />
    </asset>
    <worldbody>
      <body>
        <geom type="mesh" mesh="example_mesh"/>
      </body>
    </worldbody>
  </mujoco>
  )";
  std::array<char, 1024> error;
  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
  EXPECT_THAT(model, testing::IsNull());
  EXPECT_THAT(error.data(), HasSubstr("mesh volume is too small"));
}

TEST_F(MjCMeshTest, VolumeSmallAllowedShell) {
  static constexpr char xml[] = R"(
  <mujoco>
    <compiler convexhull="false"/>
    <asset>
      <mesh name="example_mesh"
        vertex="0 0 0  1 0 0  0 1 0  1 1 0"
        face="0 1 2  2 1 3" />
    </asset>
    <worldbody>
      <body>
        <geom type="mesh" mesh="example_mesh" shellinertia="true"/>
      </body>
    </worldbody>
  </mujoco>
  )";
  std::array<char, 1024> error;
  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
  ASSERT_THAT(model, testing::NotNull());
  EXPECT_LE(mju_abs(model->geom_size[0]), 1);
  EXPECT_LE(mju_abs(model->geom_size[1]), 1);
  EXPECT_LE(mju_abs(model->geom_size[2]), 1);
  mj_deleteModel(model);
}

TEST_F(MjCMeshTest, VolumeNegativeDefaultsLegacy) {
  static constexpr char xml[] = R"(
  <mujoco>
    <compiler exactmeshinertia="true"/>
    <asset>
      <mesh name="example_mesh"
        vertex="0 0 0  1 0 0  0 1 0  0 0 1"
        face="3 0 2  0 3 1  1 3 2  0 1 2" />
    </asset>
    <worldbody>
      <body>
        <geom type="mesh" mesh="example_mesh"/>
      </body>
    </worldbody>
  </mujoco>
  )";
  std::array<char, 1024> error;
  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
  EXPECT_THAT(model, testing::NotNull());
  EXPECT_LE(mju_abs(model->geom_size[0]), 1);
  EXPECT_LE(mju_abs(model->geom_size[1]), 1);
  EXPECT_LE(mju_abs(model->geom_size[2]), 1);
  EXPECT_THAT(error.data(), HasSubstr("Malformed"));
  mj_deleteModel(model);
}

TEST_F(MjCMeshTest, VolumeTooSmallAllowedWorld) {
  static constexpr char xml[] = R"(
  <mujoco>
    <asset>
      <mesh name="example_mesh"
        vertex="0 0 0  1 0 0  0 1 0  0 0 1"
        face="0 2 1" />
    </asset>
    <worldbody>
      <geom type="mesh" mesh="example_mesh"/>
    </worldbody>
  </mujoco>
  )";
  std::array<char, 1024> error;
  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
  EXPECT_THAT(model, testing::NotNull());
  mj_deleteModel(model);
}

// ------------- test concave and shell inertia --------------------------------

const mjtNum max_abs_err = std::numeric_limits<float>::epsilon();

TEST_F(MjCMeshTest, ExactConcaveInertia) {
  const std::string xml_path = GetTestDataFilePath(kConcaveInertiaPath);
  std::array<char, 1024> error;
  mjModel* model = mj_loadXML(xml_path.c_str(), 0, error.data(), error.size());
  // analytic computation of 1x1x1 cube with a .8x.8x.9 hole
  // see https://en.wikipedia.org/wiki/List_of_moments_of_inertia
  mjtNum m_hole = .9 * .8 * .8;
  mjtNum m_cube = 1.;
  mjtNum m_concave_cube = m_cube - m_hole;
  mjtNum I_cube = m_cube/6.;
  // due to the asymmetric hole, the com position has changed
  // so we need to use https://en.wikipedia.org/wiki/Parallel_axis_theorem
  mjtNum d_cube = .5 - model->body_ipos[5];
  mjtNum d_hole = .55 - model->body_ipos[5];
  mjtNum I1 = I_cube - m_hole*(.8*.8 + .8*.8)/12;
  mjtNum I2 = I_cube - m_hole*(.8*.8 + .9*.9)/12 + m_cube*d_cube*d_cube - m_hole*d_hole*d_hole;
  EXPECT_LE(fabs(model->body_mass[1] - m_concave_cube), max_abs_err);
  EXPECT_LE(fabs(model->body_mass[2] - m_concave_cube), max_abs_err);
  EXPECT_LE(fabs(model->body_mass[3] - m_concave_cube), max_abs_err);
  EXPECT_LE(fabs(model->body_mass[4] - m_concave_cube), max_abs_err);
  for (int i = 3; i < 15; i += 3) {
    EXPECT_LE(fabs(model->body_inertia[i] - I1), max_abs_err);
    EXPECT_LE(fabs(model->body_inertia[i+1] - I2), max_abs_err);
    EXPECT_LE(fabs(model->body_inertia[i+2] - I2), max_abs_err);
  }
  mj_deleteModel(model);
}

TEST_F(MjCMeshTest, ExactConvexInertia) {
  const std::string xml_path = GetTestDataFilePath(kConvexInertiaPath);
  std::array<char, 1024> error;
  mjModel* model = mj_loadXML(xml_path.c_str(), 0, error.data(), error.size());
  // https://en.wikipedia.org/wiki/List_of_moments_of_inertia
  mjtNum m_solid_cube = 1.;
  mjtNum I_solid_cube = 1./6. * m_solid_cube;
  EXPECT_LE(fabs(model->body_mass[1] - m_solid_cube), max_abs_err);
  EXPECT_LE(fabs(model->body_mass[2] - m_solid_cube), max_abs_err);
  for (int i = 3; i < 9; i++) {
    EXPECT_LE(fabs(model->body_inertia[i] - I_solid_cube), max_abs_err);
  }
  mj_deleteModel(model);
}

TEST_F(MjCMeshTest, ExactShellInertia) {
  const std::string xml_path = GetTestDataFilePath(kShellInertiaPath);
  std::array<char, 1024> error;
  mjModel* model = mj_loadXML(xml_path.c_str(), 0, error.data(), error.size());
  // see https://en.wikipedia.org/wiki/List_of_moments_of_inertia
  mjtNum m_hollow_cube = 6.;
  mjtNum I_hollow_cube = 5./18. * m_hollow_cube;
  EXPECT_LE(fabs(model->body_mass[1] - m_hollow_cube), max_abs_err);
  EXPECT_LE(fabs(model->body_inertia[3] - I_hollow_cube), max_abs_err);
  EXPECT_LE(fabs(model->body_inertia[4] - I_hollow_cube), max_abs_err);
  EXPECT_LE(fabs(model->body_inertia[5] - I_hollow_cube), max_abs_err);
  mj_deleteModel(model);
}

}  // namespace
}  // namespace mujoco