Mujoco_WASM/src/user/user_api.cc

// Copyright 2024 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.

#include "user/user_api.h"

#include <algorithm>
#include <cstddef>
#include <functional>
#include <iterator>
#include <map>
#include <new>
#include <string>
#include <string_view>
#include <utility>
#include <vector>

#include <mujoco/mujoco.h>
#include "user/user_model.h"
#include "user/user_objects.h"
#include "user/user_cache.h"

namespace {

using mujoco::user::StringToVector;

}  // namespace

// global cache size in bytes (default 500MB)
static constexpr std::size_t kGlobalCacheSize = 500 * (1 << 20);


// prepend prefix
template <typename T>
static T& operator+(std::string_view prefix, T& base) {
  base.prefix = std::string(prefix);
  return base;
}



// append suffix
template <typename T>
static T& operator+(T& base, std::string_view suffix) {
  base.suffix = std::string(suffix);
  return base;
}



// create model
mjSpec* mj_makeSpec() {
  mjCModel* modelC = new mjCModel;
  return &modelC->spec;
}



// copy model
mjSpec* mj_copySpec(const mjSpec* s) {
  mjCModel* modelC = new mjCModel(*static_cast<mjCModel*>(s->element));
  return &modelC->spec;
}



// copy back model
void mj_copyBack(mjSpec* s, const mjModel* m) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  modelC->CopyBack(m);
}



// compile model
mjModel* mj_compile(mjSpec* s, const mjVFS* vfs) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  return modelC->Compile(vfs);
}



// recompile spec to model, preserving the state, return 0 on success
[[nodiscard]] int mj_recompile(mjSpec* s, const mjVFS* vfs, mjModel* m, mjData* d) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  std::string state_name = "state";
  mjtNum time = 0;
  if (d) {
    time = d->time;
    modelC->SaveState(state_name, d->qpos, d->qvel, d->act, d->ctrl, d->mocap_pos, d->mocap_quat);
  }
  if (!modelC->Compile(vfs, &m)) {
    if (d) {
      mj_deleteData(d);
    }
    return -1;
  };
  if (d) {
    modelC->MakeData(m, &d);
    modelC->RestoreState(state_name, m->qpos0, m->body_pos, m->body_quat, d->qpos, d->qvel,
                         d->act, d->ctrl, d->mocap_pos, d->mocap_quat);
    d->time = time;
  }
  return 0;
}



// attach body to a frame of the parent
mjsBody* mjs_attachBody(mjsFrame* parent, const mjsBody* child,
                        const char* prefix, const char* suffix) {
  if (!parent) {
    mju_error("parent frame is null");
    return nullptr;
  }
  mjCFrame* frame_parent = static_cast<mjCFrame*>(parent->element);
  mjCBody* child_body = static_cast<mjCBody*>(child->element);
  try {
    *frame_parent += std::string(prefix) + *child_body + std::string(suffix);
  } catch (mjCError& e) {
    frame_parent->model->SetError(e);
    return nullptr;
  }
  mjsBody* attached_body = frame_parent->last_attached;
  frame_parent->last_attached = nullptr;
  return attached_body;
}



// attach frame to a parent body
mjsFrame* mjs_attachFrame(mjsBody* parent, const mjsFrame* child,
                          const char* prefix, const char* suffix) {
  if (!parent) {
    mju_error("parent body is null");
    return nullptr;
  }
  mjCBody* body_parent = static_cast<mjCBody*>(parent->element);
  mjCFrame* child_frame = static_cast<mjCFrame*>(child->element);
  try {
    *body_parent += std::string(prefix) + *child_frame + std::string(suffix);
  } catch (mjCError& e) {
    body_parent->model->SetError(e);
    return nullptr;
  }
  mjsFrame* attached_frame = body_parent->last_attached;
  body_parent->last_attached = nullptr;
  return attached_frame;
}



// get error message from model
const char* mjs_getError(mjSpec* s) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  return modelC->GetError().message;
}



// Detach body from mjSpec, return 0 if success.
int mjs_detachBody(mjSpec* s, mjsBody* b) {
  mjCModel* model = static_cast<mjCModel*>(s->element);
  mjCBody* body = static_cast<mjCBody*>(b->element);
  *model -= *body;
  delete body;
  return 0;
}



// check if model has warnings
int mjs_isWarning(mjSpec* s) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  return modelC->GetError().warning;
}



// delete model
void mj_deleteSpec(mjSpec* s) {
  if (s) {
    mjCModel* model = static_cast<mjCModel*>(s->element);
    delete model;
  }
}



// add spec (model asset) to spec
void mjs_addSpec(mjSpec* s, mjSpec* child) {
  mjCModel* model = static_cast<mjCModel*>(s->element);
  model->AppendSpec(child);
}



// activate plugin
int mjs_activatePlugin(mjSpec* s, const char* name) {
  int plugin_slot = -1;
  const mjpPlugin* plugin = mjp_getPlugin(name, &plugin_slot);
  if (!plugin) {
    mju_error("unknown plugin '%s'", name);
    return -1;
  }
  mjCModel* model = static_cast<mjCModel*>(s->element);
  model->ActivatePlugin(plugin, plugin_slot);
  return plugin_slot;
}



// delete object, it will call the appropriate destructor since ~mjCBase is virtual
void mjs_delete(mjsElement* element) {
  mjCBase* object = static_cast<mjCBase*>(element);
  object->model->DeleteElement(element);
}



// add child body to body, return child spec
mjsBody* mjs_addBody(mjsBody* bodyspec, mjsDefault* defspec) {
  mjCDef* def = defspec ? static_cast<mjCDef*>(defspec->element) : 0;
  mjCBody* body = static_cast<mjCBody*>(bodyspec->element)->AddBody(def);
  return &body->spec;
}



// add site to body, return site spec
mjsSite* mjs_addSite(mjsBody* bodyspec, mjsDefault* defspec) {
  mjCDef* def = defspec ? static_cast<mjCDef*>(defspec->element) : 0;
  mjCBody* body = static_cast<mjCBody*>(bodyspec->element);
  mjCSite* site = body->AddSite(def);
  return &site->spec;
}



// add joint to body
mjsJoint* mjs_addJoint(mjsBody* bodyspec, mjsDefault* defspec) {
  mjCDef* def = defspec ? static_cast<mjCDef*>(defspec->element) : 0;
  mjCBody* body = static_cast<mjCBody*>(bodyspec->element);
  mjCJoint* joint = body->AddJoint(def);
  return &joint->spec;
}



// add free joint to body
mjsJoint* mjs_addFreeJoint(mjsBody* bodyspec) {
  mjCBody* body = static_cast<mjCBody*>(bodyspec->element);
  mjCJoint* joint = body->AddFreeJoint();
  return &joint->spec;
}



// add geom to body
mjsGeom* mjs_addGeom(mjsBody* bodyspec, mjsDefault* defspec) {
  mjCDef* def = defspec ? static_cast<mjCDef*>(defspec->element) : 0;
  mjCBody* body = static_cast<mjCBody*>(bodyspec->element);
  mjCGeom* geom = body->AddGeom(def);
  return &geom->spec;
}



// add camera to body
mjsCamera* mjs_addCamera(mjsBody* bodyspec, mjsDefault* defspec) {
  mjCDef* def = defspec ? static_cast<mjCDef*>(defspec->element) : 0;
  mjCBody* body = static_cast<mjCBody*>(bodyspec->element);
  mjCCamera* camera = body->AddCamera(def);
  return &camera->spec;
}



// add light to body
mjsLight* mjs_addLight(mjsBody* bodyspec, mjsDefault* defspec) {
  mjCDef* def = defspec ? static_cast<mjCDef*>(defspec->element) : 0;
  mjCBody* body = static_cast<mjCBody*>(bodyspec->element);
  mjCLight* light = body->AddLight(def);
  return &light->spec;
}



// add flex to model
mjsFlex* mjs_addFlex(mjSpec* s) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCFlex* flex = modelC->AddFlex();
  return &flex->spec;
}



// add frame to body
mjsFrame* mjs_addFrame(mjsBody* bodyspec, mjsFrame* parentframe) {
  mjCFrame* parentframeC = 0;
  if (parentframe) {
    parentframeC = static_cast<mjCFrame*>(parentframe->element);
  }
  mjCBody* body = static_cast<mjCBody*>(bodyspec->element);
  mjCFrame* frameC = body->AddFrame(parentframeC);
  frameC->SetParent(body);
  return &frameC->spec;
}



// add mesh to model
mjsMesh* mjs_addMesh(mjSpec* s, mjsDefault* defspec) {
  mjCDef* def = defspec ? static_cast<mjCDef*>(defspec->element) : 0;
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCMesh* mesh = modelC->AddMesh(def);
  return &mesh->spec;
}



// add height field to model
mjsHField* mjs_addHField(mjSpec* s) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCHField* heightField = modelC->AddHField();
  return &heightField->spec;
}



// add skin to model
mjsSkin* mjs_addSkin(mjSpec* s) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCSkin* skin = modelC->AddSkin();
  return &skin->spec;
}



// add texture to model
mjsTexture* mjs_addTexture(mjSpec* s) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCTexture* texture = modelC->AddTexture();
  return &texture->spec;
}



// add material to model
mjsMaterial* mjs_addMaterial(mjSpec* s, mjsDefault* defspec) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCDef* def = defspec ? static_cast<mjCDef*>(defspec->element) : 0;
  mjCMaterial* material = modelC->AddMaterial(def);
  return &material->spec;
}



// add pair to model
mjsPair* mjs_addPair(mjSpec* s, mjsDefault* defspec) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCDef* def = defspec ? static_cast<mjCDef*>(defspec->element) : 0;
  mjCPair* pair = modelC->AddPair(def);
  return &pair->spec;
}



// add pair exclusion to model
mjsExclude* mjs_addExclude(mjSpec* s) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCBodyPair* bodypair = modelC->AddExclude();
  return &bodypair->spec;
}



// add equality to model
mjsEquality* mjs_addEquality(mjSpec* s, mjsDefault* defspec) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCDef* def = defspec ? static_cast<mjCDef*>(defspec->element) : 0;
  mjCEquality* equality = modelC->AddEquality(def);
  return &equality->spec;
}



// add tendon to model
mjsTendon* mjs_addTendon(mjSpec* s, mjsDefault* defspec) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCDef* def = defspec ? static_cast<mjCDef*>(defspec->element) : 0;
  mjCTendon* tendon = modelC->AddTendon(def);
  return &tendon->spec;
}



// wrap site using tendon
MJAPI mjsWrap* mjs_wrapSite(mjsTendon* tendonspec, const char* name) {
  mjCTendon* tendon = static_cast<mjCTendon*>(tendonspec->element);
  tendon->WrapSite(name);
  return &tendon->path.back()->spec;
}



// wrap geom using tendon
mjsWrap* mjs_wrapGeom(mjsTendon* tendonspec, const char* name, const char* sidesite) {
  mjCTendon* tendon = static_cast<mjCTendon*>(tendonspec->element);
  tendon->WrapGeom(name, sidesite);
  return &tendon->path.back()->spec;
}



// wrap joint using tendon
mjsWrap* mjs_wrapJoint(mjsTendon* tendonspec, const char* name, double coef) {
  mjCTendon* tendon = static_cast<mjCTendon*>(tendonspec->element);
  tendon->WrapJoint(name, coef);
  return &tendon->path.back()->spec;
}



// wrap pulley using tendon
mjsWrap* mjs_wrapPulley(mjsTendon* tendonspec, double divisor) {
  mjCTendon* tendon = static_cast<mjCTendon*>(tendonspec->element);
  tendon->WrapPulley(divisor);
  return &tendon->path.back()->spec;
}



// add actuator to model
mjsActuator* mjs_addActuator(mjSpec* s, mjsDefault* defspec) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCDef* def = defspec ? static_cast<mjCDef*>(defspec->element) : 0;
  mjCActuator* actuator = modelC->AddActuator(def);
  return &actuator->spec;
}



// add sensor to model
mjsSensor* mjs_addSensor(mjSpec* s) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCSensor* sensor = modelC->AddSensor();
  return &sensor->spec;
}



// add numeric to model
mjsNumeric* mjs_addNumeric(mjSpec* s) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCNumeric* numeric = modelC->AddNumeric();
  return &numeric->spec;
}



// add text to model
mjsText* mjs_addText(mjSpec* s) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCText* text = modelC->AddText();
  return &text->spec;
}



// add tuple to model
mjsTuple* mjs_addTuple(mjSpec* s) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCTuple* tuple = modelC->AddTuple();
  return &tuple->spec;
}



// add keyframe to model
mjsKey* mjs_addKey(mjSpec* s) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCKey* key = modelC->AddKey();
  return &key->spec;
}



// add plugin to model
mjsPlugin* mjs_addPlugin(mjSpec* s) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCPlugin* plugin = modelC->AddPlugin();
  plugin->spec.element = static_cast<mjsElement*>(plugin);
  return &plugin->spec;
}



// add default to model
mjsDefault* mjs_addDefault(mjSpec* s, const char* classname, const mjsDefault* parent) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCDef* parentC = parent ? static_cast<mjCDef*>(parent->element) :
                             static_cast<mjCModel*>(s->element)->Default();
  mjCDef* def = modelC->AddDefault(classname, parentC);
  if (def) {
    return &def->spec;
  } else {
    return nullptr;
  }
}



// get objects
mjSpec* mjs_getSpec(mjsBody* body) {
  return &(static_cast<mjCBody*>(body->element)->model->spec);
}



// find spec (model asset) by name
mjSpec* mjs_findSpec(mjSpec* s, const char* name) {
  mjCModel* model = static_cast<mjCModel*>(s->element);
  return model->FindSpec(name);
}



// get default
mjsDefault* mjs_getDefault(mjsElement* element) {
  mjCModel* model = static_cast<mjCBase*>(element)->model;
  std::string classname = static_cast<mjCBase*>(element)->classname;
  return &(model->def_map[classname]->spec);
}



// Find default with given name in model.
mjsDefault* mjs_findDefault(mjSpec* s, const char* classname) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCDef* cdef = modelC->FindDefault(classname);
  if (!cdef) {
    return nullptr;
  }
  return &cdef->spec;
}



// get default[0] from model
mjsDefault* mjs_getSpecDefault(mjSpec* s) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  mjCDef* def = modelC->Default();
  if (!def) {
    return nullptr;
  }
  return &def->spec;
}



// find body in model by name
mjsBody* mjs_findBody(mjSpec* s, const char* name) {
  mjsElement* body = mjs_findElement(s, mjOBJ_BODY, name);
  return body ? &(static_cast<mjCBody*>(body)->spec) : nullptr;
}



// find element in spec by name
mjsElement* mjs_findElement(mjSpec* s, mjtObj type, const char* name) {
  mjCModel* model = static_cast<mjCModel*>(s->element);
  if (model->IsCompiled()) {
    return model->FindObject(type, std::string(name));  // fast lookup
  }
  switch (type) {
    case mjOBJ_BODY:
    case mjOBJ_SITE:
    case mjOBJ_GEOM:
    case mjOBJ_JOINT:
    case mjOBJ_CAMERA:
    case mjOBJ_LIGHT:
    case mjOBJ_FRAME:
      return model->FindTree(model->GetWorld(), type, std::string(name));  // recursive search
    default:
      return model->FindObject(type, std::string(name));  // always available
  }
}



// find child of a body by name
mjsBody* mjs_findChild(mjsBody* bodyspec, const char* name) {
  mjCBody* body = static_cast<mjCBody*>(bodyspec->element);
  mjCBase* child = body->FindObject(mjOBJ_BODY, std::string(name));
  return child ? &(static_cast<mjCBody*>(child)->spec) : nullptr;
}



// find frame by name
mjsFrame* mjs_findFrame(mjSpec* s, const char* name) {
  mjsElement* frame = mjs_findElement(s, mjOBJ_FRAME, name);
  return frame ? &(static_cast<mjCFrame*>(frame)->spec) : nullptr;
}



// set frame
void mjs_setFrame(mjsElement* dest, mjsFrame* frame) {
  if (!frame) {
    return;
  }
  mjCFrame* frameC = static_cast<mjCFrame*>(frame->element);
  mjCBase* baseC = static_cast<mjCBase*>(dest);
  baseC->SetFrame(frameC);
}



// Resolve alternative orientations.
const char* mjs_resolveOrientation(double quat[4], mjtByte degree, const char* sequence,
                                   const mjsOrientation* orientation) {
  return ResolveOrientation(quat, degree, sequence, *orientation);
}



// get id
int mjs_getId(mjsElement* element) {
  if (!element) {
    return -1;
  }
  return static_cast<mjCBase*>(element)->id;
}



// set default
void mjs_setDefault(mjsElement* element, mjsDefault* defspec) {
  mjCBase* baseC = static_cast<mjCBase*>(element);
  baseC->classname = static_cast<mjCDef*>(defspec->element)->name;
}



// return first child of selected type
mjsElement* mjs_firstChild(mjsBody* body, mjtObj type, int recurse) {
  mjCBody* bodyC = static_cast<mjCBody*>(body->element);
  try {
    return bodyC->NextChild(NULL, type, recurse);
  } catch (mjCError& e) {
    bodyC->model->SetError(e);
    return nullptr;
  }
}



// return body's next child; return NULL if child is last
mjsElement* mjs_nextChild(mjsBody* body, mjsElement* child, int recurse) {
  mjCBody* bodyC = static_cast<mjCBody*>(body->element);
  try {
    return bodyC->NextChild(child, child->elemtype, recurse);
  } catch(mjCError& e) {
    bodyC->model->SetError(e);
    return nullptr;
  }
}



// return spec's first element of selected type
mjsElement* mjs_firstElement(mjSpec* s, mjtObj type) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  return modelC->NextObject(NULL, type);
}



// return spec's next element; return NULL if element is last
mjsElement* mjs_nextElement(mjSpec* s, mjsElement* element) {
  mjCModel* modelC = static_cast<mjCModel*>(s->element);
  return modelC->NextObject(element);
}



// return body given mjsElement
mjsBody* mjs_asBody(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_BODY) {
    return &(static_cast<mjCBody*>(element)->spec);
  }
  return nullptr;
}



// return geom given mjsElement
mjsGeom* mjs_asGeom(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_GEOM) {
    return &(static_cast<mjCGeom*>(element)->spec);
  }
  return nullptr;
}



// return joint given mjsElement
mjsJoint* mjs_asJoint(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_JOINT) {
    return &(static_cast<mjCJoint*>(element)->spec);
  }
  return nullptr;
}



// Return site given mjsElement
mjsSite* mjs_asSite(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_SITE) {
    return &(static_cast<mjCSite*>(element)->spec);
  }
  return nullptr;
}



// return camera given mjsElement
mjsCamera* mjs_asCamera(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_CAMERA) {
    return &(static_cast<mjCCamera*>(element)->spec);
  }
  return nullptr;
}



// return light given mjsElement
mjsLight* mjs_asLight(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_LIGHT) {
    return &(static_cast<mjCLight*>(element)->spec);
  }
  return nullptr;
}



// return frame given mjsElement
mjsFrame* mjs_asFrame(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_FRAME) {
    return &(static_cast<mjCFrame*>(element)->spec);
  }
  return nullptr;
}



// return actuator given mjsElement
mjsActuator* mjs_asActuator(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_ACTUATOR) {
    return &(static_cast<mjCActuator*>(element)->spec);
  }
  return nullptr;
}



// return sensor given mjsElement
mjsSensor* mjs_asSensor(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_SENSOR) {
    return &(static_cast<mjCSensor*>(element)->spec);
  }
  return nullptr;
}



// return flex given mjsElement
mjsFlex* mjs_asFlex(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_FLEX) {
    return &(static_cast<mjCFlex*>(element)->spec);
  }
  return nullptr;
}



// return pair given mjsElement
mjsPair* mjs_asPair(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_PAIR) {
    return &(static_cast<mjCPair*>(element)->spec);
  }
  return nullptr;
}



// return equality given mjsElement
mjsEquality* mjs_asEquality(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_EQUALITY) {
    return &(static_cast<mjCEquality*>(element)->spec);
  }
  return nullptr;
}



// return exclude given mjsElement
mjsExclude* mjs_asExclude(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_EXCLUDE) {
    return &(static_cast<mjCBodyPair*>(element)->spec);
  }
  return nullptr;
}



// return tendon given mjsElement
mjsTendon* mjs_asTendon(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_TENDON) {
    return &(static_cast<mjCTendon*>(element)->spec);
  }
  return nullptr;
}



// return numeric given mjsElement
mjsNumeric* mjs_asNumeric(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_NUMERIC) {
    return &(static_cast<mjCNumeric*>(element)->spec);
  }
  return nullptr;
}



// return text given mjsElement
mjsText* mjs_asText(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_TEXT) {
    return &(static_cast<mjCText*>(element)->spec);
  }
  return nullptr;
}



// return tuple given mjsElement
mjsTuple* mjs_asTuple(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_TUPLE) {
    return &(static_cast<mjCTuple*>(element)->spec);
  }
  return nullptr;
}



// return key given mjsElement
mjsKey* mjs_asKey(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_KEY) {
    return &(static_cast<mjCKey*>(element)->spec);
  }
  return nullptr;
}



// return mesh given mjsElement
mjsMesh* mjs_asMesh(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_MESH) {
    return &(static_cast<mjCMesh*>(element)->spec);
  }
  return nullptr;
}



// return hfield given mjsElement
mjsHField* mjs_asHField(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_HFIELD) {
    return &(static_cast<mjCHField*>(element)->spec);
  }
  return nullptr;
}



// return skin given mjsElement
mjsSkin* mjs_asSkin(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_SKIN) {
    return &(static_cast<mjCSkin*>(element)->spec);
  }
  return nullptr;
}



// return texture given mjsElement
mjsTexture* mjs_asTexture(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_TEXTURE) {
    return &(static_cast<mjCTexture*>(element)->spec);
  }
  return nullptr;
}



// return material given mjsElement
mjsMaterial* mjs_asMaterial(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_MATERIAL) {
    return &(static_cast<mjCMaterial*>(element)->spec);
  }
  return nullptr;
}



// return plugin given mjsElement
mjsPlugin* mjs_asPlugin(mjsElement* element) {
  if (element && element->elemtype == mjOBJ_PLUGIN) {
    return &(static_cast<mjCPlugin*>(element)->spec);
  }
  return nullptr;
}



// copy buffer to destination buffer
void mjs_setBuffer(mjByteVec* dest, const void* array, int size) {
  const std::byte* buffer = static_cast<const std::byte*>(array);
  dest->clear();
  dest->reserve(size);
  std::copy_n(buffer, size, std::back_inserter(*dest));
}



// set string
void mjs_setString(mjString* dest, const char* text) {
  std::string* str = static_cast<std::string*>(dest);
  *str = std::string(text);
}



// Set specific entry in destination string vector.
mjtByte mjs_setInStringVec(mjStringVec* dest, int i, const char* text) {
  if (dest->size() <= i) {
    mju_error("Requested index in mjs_setInStringVec is out of bounds");
    return 0;
  }
  dest->at(i) = std::string(text);
  return 1;
}



// split text and copy into string array
void mjs_setStringVec(mjStringVec* dest, const char* text) {
  std::vector<std::string>* v = static_cast<std::vector<std::string>*>(dest);
  *v = StringToVector<std::string>(text);
}



// add text entry to destination string vector
void mjs_appendString(mjStringVec* dest, const char* text) {
  dest->push_back(std::string(text));
}


// copy int array to vector
void mjs_setInt(mjIntVec* dest, const int* array, int size) {
  dest->assign(size, 0.0);
  for (int i = 0; i < size; ++i) {
    (*dest)[i] = array[i];
  }
}



// append int array to vector of arrays
void mjs_appendIntVec(mjIntVecVec* dest, const int* array, int size) {
  dest->push_back(std::vector<int>(array, array + size));
}



// copy float array to vector
void mjs_setFloat(mjFloatVec* dest, const float* array, int size) {
  dest->assign(size, 0.0);
  for (int i = 0; i < size; ++i) {
    (*dest)[i] = array[i];
  }
}




// append float array to vector of arrays
void mjs_appendFloatVec(mjFloatVecVec* dest, const float* array, int size) {
  dest->push_back(std::vector<float>(array, array + size));
}



// copy double array to vector
void mjs_setDouble(mjDoubleVec* dest, const double* array, int size) {
  dest->assign(size, 0.0);
  for (int i = 0; i < size; ++i) {
    (*dest)[i] = array[i];
  }
}



// get string
const char* mjs_getString(const mjString* source) {
  return source->c_str();
}



// get double array
const double* mjs_getDouble(const mjDoubleVec* source, int* size) {
  if (size) {
    *size = source->size();
  }
  return source->data();
}



// set plugin attributes
void mjs_setPluginAttributes(mjsPlugin* plugin, void* attributes) {
  mjCPlugin* pluginC = static_cast<mjCPlugin*>(plugin->element);
  std::map<std::string, std::string, std::less<>>* config_attribs =
      reinterpret_cast<std::map<std::string, std::string, std::less<>>*>(attributes);
  pluginC->config_attribs = std::move(*config_attribs);
}



// -------------------------- GLOBAL ASSET CACHE -------------------------------

void mj_setCacheSize(mjCache cache, std::size_t size) {
  mjCCache* ccache = reinterpret_cast<mjCCache*>(cache);
  if (ccache) {
    ccache->SetMaxSize(size);
  }
}



mjCache mj_globalCache() {
  // mjCCache is not trivially destructible and so the global cache needs to
  // allocated on the heap
  if constexpr (kGlobalCacheSize != 0) {
    static mjCCache* cache = new(std::nothrow) mjCCache(kGlobalCacheSize);
    return (mjCache) cache;
  } else {
    return NULL;
  }
}