EntityComponentManager.cc

/*
 * Copyright (C) 2018 Open Source Robotics Foundation
 *
 * 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 <map>
#include <set>
#include <vector>

#include <ignition/common/Profiler.hh>
#include <ignition/math/graph/GraphAlgorithms.hh>
#include "ignition/gazebo/components/Component.hh"
#include "ignition/gazebo/components/Factory.hh"
#include "ignition/gazebo/EntityComponentManager.hh"

using namespace ignition;
using namespace gazebo;

class ignition::gazebo::EntityComponentManagerPrivate
{
  /// \brief Implementation of the CreateEntity function, which takes a specific
  /// entity as input.
  /// \param[in] _entity Entity to be created.
  /// \return Created entity, which should match the input.
  public: Entity CreateEntityImplementation(Entity _entity);

  /// \brief Recursively insert an entity and all its descendants into a given
  /// set.
  /// \param[in] _entity Entity to be inserted.
  /// \param[in, out] _set Set to be filled.
  public: void InsertEntityRecursive(Entity _entity,
      std::set<Entity> &_set);

  /// \brief Register a new component type.
  /// \param[in] _typeId Type if of the new component.
  /// \return True if created successfully.
  public: bool CreateComponentStorage(const ComponentTypeId _typeId);

  /// \brief Map of component storage classes. The key is a component
  /// type id, and the value is a pointer to the component storage.
  public: std::map<ComponentTypeId,
          std::unique_ptr<ComponentStorageBase>> components;

  /// \brief A graph holding all entities, arranged according to their
  /// parenting.
  public: EntityGraph entities;

  /// \brief Components that have been changed through a peridic change.
  public: std::set<ComponentKey> periodicChangedComponents;

  /// \brief Components that have been changed through a one-time change.
  public: std::set<ComponentKey> oneTimeChangedComponents;

  /// \brief Entities that have just been created
  public: std::set<Entity> newlyCreatedEntities;

  /// \brief Entities that need to be removed.
  public: std::set<Entity> toRemoveEntities;

  /// \brief Flag that indicates if all entities should be removed.
  public: bool removeAllEntities{false};

  /// \brief The set of components that each entity has
  public: std::map<Entity, std::vector<ComponentKey>> entityComponents;

  /// \brief A mutex to protect newly created entityes.
  public: std::mutex entityCreatedMutex;

  /// \brief A mutex to protect entity remove.
  public: std::mutex entityRemoveMutex;

  /// \brief A mutex to protect from concurrent writes to views
  public: mutable std::mutex viewsMutex;

  /// \brief The set of all views.
  public: mutable std::map<detail::ComponentTypeKey, detail::View> views;

  /// \brief Cache of previously queried descendants. The key is the parent
  /// entity for which descendants were queried, and the value are all its
  /// descendants.
  public: mutable std::map<Entity, std::unordered_set<Entity>> descendantCache;

  /// \brief Keep track of entities already used to ensure uniqueness.
  public: uint64_t entityCount{0};
};

//////////////////////////////////////////////////
EntityComponentManager::EntityComponentManager()
  : dataPtr(new EntityComponentManagerPrivate)
{
}

//////////////////////////////////////////////////
EntityComponentManager::~EntityComponentManager() = default;

//////////////////////////////////////////////////
size_t EntityComponentManager::EntityCount() const
{
  return this->dataPtr->entities.Vertices().size();
}

/////////////////////////////////////////////////
Entity EntityComponentManager::CreateEntity()
{
  Entity entity = ++this->dataPtr->entityCount;

  if (entity == std::numeric_limits<int64_t>::max())
  {
    ignwarn << "Reached maximum number of entities [" << entity << "]"
            << std::endl;
    return entity;
  }

  return this->dataPtr->CreateEntityImplementation(entity);
}

/////////////////////////////////////////////////
Entity EntityComponentManagerPrivate::CreateEntityImplementation(Entity _entity)
{
  IGN_PROFILE("EntityComponentManager::CreateEntityImplementation");
  this->entities.AddVertex(std::to_string(_entity), _entity, _entity);

  // Add entity to the list of newly created entities
  {
    std::lock_guard<std::mutex> lock(this->entityCreatedMutex);
    this->newlyCreatedEntities.insert(_entity);
  }

  // Reset descendants cache
  this->descendantCache.clear();

  return _entity;
}

/////////////////////////////////////////////////
void EntityComponentManager::ClearNewlyCreatedEntities()
{
  std::lock_guard<std::mutex> lock(this->dataPtr->entityCreatedMutex);
  this->dataPtr->newlyCreatedEntities.clear();

  for (auto &view : this->dataPtr->views)
  {
    view.second.ClearNewEntities();
  }
}

/////////////////////////////////////////////////
void EntityComponentManagerPrivate::InsertEntityRecursive(Entity _entity,
    std::set<Entity> &_set)
{
  for (const auto &vertex : this->entities.AdjacentsFrom(_entity))
  {
    this->InsertEntityRecursive(vertex.first, _set);
  }
  _set.insert(_entity);
}

/////////////////////////////////////////////////
void EntityComponentManager::RequestRemoveEntity(Entity _entity,
    bool _recursive)
{
  // Store the to-be-removed entities in a temporary set so we can call
  // UpdateViews on each of them
  std::set<Entity> tmpToRemoveEntities;
  if (!_recursive)
  {
    tmpToRemoveEntities.insert(_entity);
  }
  else
  {
    this->dataPtr->InsertEntityRecursive(_entity, tmpToRemoveEntities);
  }

  {
    std::lock_guard<std::mutex> lock(this->dataPtr->entityRemoveMutex);
    this->dataPtr->toRemoveEntities.insert(tmpToRemoveEntities.begin(),
                                          tmpToRemoveEntities.end());
  }

  for (const auto &removedEntity : tmpToRemoveEntities)
  {
    this->UpdateViews(removedEntity);
  }
}

/////////////////////////////////////////////////
void EntityComponentManager::RequestRemoveEntities()
{
  {
    std::lock_guard<std::mutex> lock(this->dataPtr->entityRemoveMutex);
    this->dataPtr->removeAllEntities = true;
  }
  this->RebuildViews();
}

/////////////////////////////////////////////////
void EntityComponentManager::ProcessRemoveEntityRequests()
{
  IGN_PROFILE("EntityComponentManager::ProcessRemoveEntityRequests");
  std::lock_guard<std::mutex> lock(this->dataPtr->entityRemoveMutex);
  // Short-cut if erasing all entities
  if (this->dataPtr->removeAllEntities)
  {
    IGN_PROFILE("RemoveAll");
    this->dataPtr->removeAllEntities = false;
    this->dataPtr->entities = EntityGraph();
    this->dataPtr->entityComponents.clear();
    this->dataPtr->toRemoveEntities.clear();

    for (std::pair<const ComponentTypeId,
        std::unique_ptr<ComponentStorageBase>> &comp: this->dataPtr->components)
    {
      comp.second->RemoveAll();
    }

    // All views are now invalid.
    this->dataPtr->views.clear();
  }
  else
  {
    IGN_PROFILE("Remove");
    // Otherwise iterate through the list of entities to remove.
    for (const Entity entity : this->dataPtr->toRemoveEntities)
    {
      // Make sure the entity exists and is not removed.
      if (!this->HasEntity(entity))
        continue;

      // Remove from graph
      this->dataPtr->entities.RemoveVertex(entity);

      // Remove the components, if any.
      if (this->dataPtr->entityComponents.find(entity) !=
          this->dataPtr->entityComponents.end())
      {
        for (const ComponentKey &key :
            this->dataPtr->entityComponents.at(entity))
        {
          this->dataPtr->components.at(key.first)->Remove(key.second);
        }

        // Remove the entry in the entityComponent map
        this->dataPtr->entityComponents.erase(entity);
      }

      // Remove the entity from views.
      for (auto &view : this->dataPtr->views)
      {
        view.second.RemoveEntity(entity, view.first);
      }
    }
    // Clear the set of entities to remove.
    this->dataPtr->toRemoveEntities.clear();
  }

  // Reset descendants cache
  this->dataPtr->descendantCache.clear();
}

/////////////////////////////////////////////////
bool EntityComponentManager::RemoveComponent(
    const Entity _entity, const ComponentTypeId &_typeId)
{
  auto componentId = this->EntityComponentIdFromType(_entity, _typeId);
  ComponentKey key{_typeId, componentId};
  return this->RemoveComponent(_entity, key);
}

/////////////////////////////////////////////////
bool EntityComponentManager::RemoveComponent(
    const Entity _entity, const ComponentKey &_key)
{
  IGN_PROFILE("EntityComponentManager::RemoveComponent");
  // Make sure the entity exists and has the component.
  if (!this->EntityHasComponent(_entity, _key))
    return false;

  auto entityComponentIter = std::find(
      this->dataPtr->entityComponents[_entity].begin(),
      this->dataPtr->entityComponents[_entity].end(), _key);

  this->dataPtr->components.at(_key.first)->Remove(_key.second);
  this->dataPtr->entityComponents[_entity].erase(entityComponentIter);
  this->dataPtr->oneTimeChangedComponents.erase(_key);
  this->dataPtr->periodicChangedComponents.erase(_key);

  this->UpdateViews(_entity);
  return true;
}

/////////////////////////////////////////////////
bool EntityComponentManager::EntityHasComponent(const Entity _entity,
    const ComponentKey &_key) const
{
  return this->HasEntity(_entity) &&
    std::find(this->dataPtr->entityComponents[_entity].begin(),
        this->dataPtr->entityComponents[_entity].end(), _key) !=
    this->dataPtr->entityComponents[_entity].end();
}

/////////////////////////////////////////////////
bool EntityComponentManager::EntityHasComponentType(const Entity _entity,
    const ComponentTypeId &_typeId) const
{
  if (!this->HasEntity(_entity))
    return false;

  auto iter = this->dataPtr->entityComponents.find(_entity);

  if (iter == this->dataPtr->entityComponents.end())
    return false;

  return std::find_if(iter->second.begin(), iter->second.end(),
      [&] (const ComponentKey &_key)
      {
        return _key.first == _typeId;
      }) != iter->second.end();
}

/////////////////////////////////////////////////
bool EntityComponentManager::IsNewEntity(const Entity _entity) const
{
  std::lock_guard<std::mutex> lock(this->dataPtr->entityCreatedMutex);
  return this->dataPtr->newlyCreatedEntities.find(_entity) !=
         this->dataPtr->newlyCreatedEntities.end();
}

/////////////////////////////////////////////////
bool EntityComponentManager::IsMarkedForRemoval(const Entity _entity) const
{
  std::lock_guard<std::mutex> lock(this->dataPtr->entityRemoveMutex);
  if (this->dataPtr->removeAllEntities)
  {
    return true;
  }
  return this->dataPtr->toRemoveEntities.find(_entity) !=
         this->dataPtr->toRemoveEntities.end();
}

/////////////////////////////////////////////////
ComponentState EntityComponentManager::ComponentState(const Entity _entity,
    const ComponentTypeId _typeId) const
{
  auto result = ComponentState::NoChange;

  auto ecIter = this->dataPtr->entityComponents.find(_entity);

  if (ecIter == this->dataPtr->entityComponents.end())
    return result;

  auto iter = std::find_if(ecIter->second.begin(), ecIter->second.end(),
        [&] (const ComponentKey &_key)
  {
    return _key.first == _typeId;
  });

  if (iter == ecIter->second.end())
    return result;

  if (this->dataPtr->oneTimeChangedComponents.find(*iter) !=
      this->dataPtr->oneTimeChangedComponents.end())
  {
    result = ComponentState::OneTimeChange;
  }
  else if (this->dataPtr->periodicChangedComponents.find(*iter) !=
      this->dataPtr->periodicChangedComponents.end())
  {
    result = ComponentState::PeriodicChange;
  }

  return result;
}

/////////////////////////////////////////////////
bool EntityComponentManager::HasNewEntities() const
{
  std::lock_guard<std::mutex> lock(this->dataPtr->entityCreatedMutex);
  return !this->dataPtr->newlyCreatedEntities.empty();
}

/////////////////////////////////////////////////
bool EntityComponentManager::HasEntitiesMarkedForRemoval() const
{
  std::lock_guard<std::mutex> lock(this->dataPtr->entityRemoveMutex);
  return this->dataPtr->removeAllEntities ||
      !this->dataPtr->toRemoveEntities.empty();
}

/////////////////////////////////////////////////
bool EntityComponentManager::HasOneTimeComponentChanges() const
{
  return !this->dataPtr->oneTimeChangedComponents.empty();
}

/////////////////////////////////////////////////
bool EntityComponentManager::HasEntity(const Entity _entity) const
{
  auto vertex = this->dataPtr->entities.VertexFromId(_entity);
  return vertex.Id() != math::graph::kNullId;
}

/////////////////////////////////////////////////
Entity EntityComponentManager::ParentEntity(const Entity _entity) const
{
  auto parents = this->Entities().AdjacentsTo(_entity);
  if (parents.empty())
    return kNullEntity;

  // TODO(louise) Do we want to support multiple parents?
  return parents.begin()->first;
}

/////////////////////////////////////////////////
bool EntityComponentManager::SetParentEntity(const Entity _child,
    const Entity _parent)
{
  // Remove current parent(s)
  auto parents = this->Entities().AdjacentsTo(_child);
  for (const auto &parent : parents)
  {
    auto edge = this->dataPtr->entities.EdgeFromVertices(parent.first, _child);
    this->dataPtr->entities.RemoveEdge(edge);
  }

  // Leave parent-less
  if (_parent == kNullEntity)
  {
    return true;
  }

  // Add edge
  auto edge = this->dataPtr->entities.AddEdge({_parent, _child}, true);
  return (math::graph::kNullId != edge.Id());
}

/////////////////////////////////////////////////
ComponentKey EntityComponentManager::CreateComponentImplementation(
    const Entity _entity, const ComponentTypeId _componentTypeId,
    const components::BaseComponent *_data)
{
  // If type hasn't been instantiated yet, create a storage for it
  if (!this->HasComponentType(_componentTypeId))
  {
    if (!this->dataPtr->CreateComponentStorage(_componentTypeId))
    {
      ignerr << "Failed to create component of type [" << _componentTypeId
             << "] for entity [" << _entity
             << "]. Type has not been properly registered." << std::endl;
      return ComponentKey();
    }
  }

  // Instantiate the new component.
  std::pair<ComponentId, bool> componentIdPair =
    this->dataPtr->components[_componentTypeId]->Create(_data);

  ComponentKey componentKey{_componentTypeId, componentIdPair.first};

  this->dataPtr->entityComponents[_entity].push_back(componentKey);
  this->dataPtr->oneTimeChangedComponents.insert(componentKey);

  if (componentIdPair.second)
    this->RebuildViews();
  else
    this->UpdateViews(_entity);

  return componentKey;
}

/////////////////////////////////////////////////
bool EntityComponentManager::EntityMatches(Entity _entity,
    const std::set<ComponentTypeId> &_types) const
{
  auto iter = this->dataPtr->entityComponents.find(_entity);
  if (iter == this->dataPtr->entityComponents.end())
    return false;

  // \todo(nkoenig) The performance of this could be improved. Ideally we
  // wouldn't need two loops to confirm that an entity matches a set of
  // types. It might be possible to create bitmask for component sets.
  // Fixing this might not be high priority, unless we expect frequent
  // creation of entities and/or queries.
  for (const ComponentTypeId &type : _types)
  {
    bool found = false;
    for (const ComponentKey &comp : iter->second)
    {
      if (comp.first == type)
      {
        found = true;
        break;
      }
    }
    if (!found)
      return false;
  }

  return true;
}

/////////////////////////////////////////////////
ComponentId EntityComponentManager::EntityComponentIdFromType(
    const Entity _entity, const ComponentTypeId _type) const
{
  auto ecIter = this->dataPtr->entityComponents.find(_entity);

  if (ecIter == this->dataPtr->entityComponents.end())
    return -1;

  auto iter =
    std::find_if(ecIter->second.begin(), ecIter->second.end(),
      [&] (const ComponentKey &_key)
  {
    return _key.first == _type;
  });

  if (iter != ecIter->second.end())
    return iter->second;

  return -1;
}

/////////////////////////////////////////////////
const components::BaseComponent
    *EntityComponentManager::ComponentImplementation(
    const Entity _entity, const ComponentTypeId _type) const
{
  IGN_PROFILE("EntityComponentManager::ComponentImplementation");
  auto ecIter = this->dataPtr->entityComponents.find(_entity);

  if (ecIter == this->dataPtr->entityComponents.end())
    return nullptr;

  auto iter = std::find_if(ecIter->second.begin(), ecIter->second.end(),
      [&] (const ComponentKey &_key)
  {
    return _key.first == _type;
  });

  if (iter != ecIter->second.end())
    return this->dataPtr->components.at(iter->first)->Component(iter->second);

  return nullptr;
}

/////////////////////////////////////////////////
components::BaseComponent *EntityComponentManager::ComponentImplementation(
    const Entity _entity, const ComponentTypeId _type)
{
  auto ecIter = this->dataPtr->entityComponents.find(_entity);

  if (ecIter == this->dataPtr->entityComponents.end())
    return nullptr;

  auto iter =
    std::find_if(ecIter->second.begin(), ecIter->second.end(),
        [&] (const ComponentKey &_key)
  {
    return _key.first == _type;
  });

  if (iter != ecIter->second.end())
    return this->dataPtr->components.at(iter->first)->Component(iter->second);

  return nullptr;
}

/////////////////////////////////////////////////
const components::BaseComponent
    *EntityComponentManager::ComponentImplementation(
    const ComponentKey &_key) const
{
  if (this->dataPtr->components.find(_key.first) !=
      this->dataPtr->components.end())
  {
    return this->dataPtr->components.at(_key.first)->Component(_key.second);
  }
  return nullptr;
}

/////////////////////////////////////////////////
components::BaseComponent *EntityComponentManager::ComponentImplementation(
    const ComponentKey &_key)
{
  if (this->dataPtr->components.find(_key.first) !=
      this->dataPtr->components.end())
  {
    return this->dataPtr->components.at(_key.first)->Component(_key.second);
  }
  return nullptr;
}

/////////////////////////////////////////////////
bool EntityComponentManager::HasComponentType(
    const ComponentTypeId _typeId) const
{
  return this->dataPtr->components.find(_typeId) !=
    this->dataPtr->components.end();
}

/////////////////////////////////////////////////
bool EntityComponentManagerPrivate::CreateComponentStorage(
    const ComponentTypeId _typeId)
{
  auto storage = components::Factory::Instance()->NewStorage(_typeId);

  if (nullptr == storage)
  {
    ignerr << "Internal errror: failed to create storage for type [" << _typeId
           << "]" << std::endl;
    return false;
  }

  this->components[_typeId] = std::move(storage);
  igndbg << "Using components of type [" << _typeId << "] / ["
         << components::Factory::Instance()->Name(_typeId) << "].\n";

  return true;
}

/////////////////////////////////////////////////
components::BaseComponent *EntityComponentManager::First(
    const ComponentTypeId _componentTypeId)
{
  auto iter = this->dataPtr->components.find(_componentTypeId);
  if (iter != this->dataPtr->components.end())
  {
    return iter->second->First();
  }
  return nullptr;
}

//////////////////////////////////////////////////
const EntityGraph &EntityComponentManager::Entities() const
{
  return this->dataPtr->entities;
}

//////////////////////////////////////////////////
bool EntityComponentManager::FindView(const std::set<ComponentTypeId> &_types,
    std::map<detail::ComponentTypeKey, detail::View>::iterator &_iter) const
{
  std::lock_guard<std::mutex> lockViews(this->dataPtr->viewsMutex);
  _iter = this->dataPtr->views.find(_types);
  return _iter != this->dataPtr->views.end();
}

//////////////////////////////////////////////////
std::map<detail::ComponentTypeKey, detail::View>::iterator
    EntityComponentManager::AddView(const std::set<ComponentTypeId> &_types,
    detail::View &&_view) const
{
  // If the view already exists, then the map will return the iterator to
  // the location that prevented the insertion.
  std::lock_guard<std::mutex> lockViews(this->dataPtr->viewsMutex);
  return this->dataPtr->views.insert(
      std::make_pair(_types, std::move(_view))).first;
}

//////////////////////////////////////////////////
void EntityComponentManager::UpdateViews(const Entity _entity)
{
  IGN_PROFILE("EntityComponentManager::UpdateViews");
  for (auto &view : this->dataPtr->views)
  {
    // Add/update the entity if it matches the view.
    if (this->EntityMatches(_entity, view.first))
    {
      view.second.AddEntity(_entity, this->IsNewEntity(_entity));
      // If there is a request to delete this entity, update the view as
      // well
      if (this->IsMarkedForRemoval(_entity))
      {
        view.second.AddEntityToRemoved(_entity);
      }
      for (const ComponentTypeId &compTypeId : view.first)
      {
        view.second.AddComponent(_entity, compTypeId,
            this->EntityComponentIdFromType(_entity, compTypeId));
      }
    }
    else
    {
      view.second.RemoveEntity(_entity, view.first);
    }
  }
}

//////////////////////////////////////////////////
void EntityComponentManager::RebuildViews()
{
  IGN_PROFILE("EntityComponentManager::RebuildViews");
  for (auto &view : this->dataPtr->views)
  {
    view.second.entities.clear();
    view.second.components.clear();
    // Add all the entities that match the component types to the
    // view.
    for (const auto &vertex : this->dataPtr->entities.Vertices())
    {
      Entity entity = vertex.first;
      if (this->EntityMatches(entity, view.first))
      {
        view.second.AddEntity(entity, this->IsNewEntity(entity));
        // If there is a request to delete this entity, update the view as
        // well
        if (this->IsMarkedForRemoval(entity))
        {
          view.second.AddEntityToRemoved(entity);
        }
        // Store pointers to all the components. This recursively adds
        // all the ComponentTypeTs that belong to the entity to the view.
        for (const ComponentTypeId &compTypeId : view.first)
        {
          view.second.AddComponent(entity, compTypeId,
              this->EntityComponentIdFromType(
                entity, compTypeId));
        }
      }
    }
  }
}

//////////////////////////////////////////////////
void EntityComponentManager::AddEntityToMessage(msgs::SerializedState &_msg,
    Entity _entity, const std::unordered_set<ComponentTypeId> &_types) const
{
  auto entityMsg = _msg.add_entities();
  entityMsg->set_id(_entity);

  if (this->dataPtr->toRemoveEntities.find(_entity) !=
      this->dataPtr->toRemoveEntities.end())
  {
    entityMsg->set_remove(true);
  }

  // Empty means all types
  bool allTypes = _types.empty();

  auto components = this->dataPtr->entityComponents[_entity];
  for (const auto &comp : components)
  {
    if (!allTypes && _types.find(comp.first) == _types.end())
    {
      continue;
    }

    auto compMsg = entityMsg->add_components();

    auto compBase = this->ComponentImplementation(_entity, comp.first);
    compMsg->set_type(compBase->TypeId());

    std::ostringstream ostr;
    compBase->Serialize(ostr);

    compMsg->set_component(ostr.str());

    // TODO(anyone) Set component being removed once we have a way to queue it
  }
}

//////////////////////////////////////////////////
void EntityComponentManager::AddEntityToMessage(msgs::SerializedStateMap &_msg,
    Entity _entity, const std::unordered_set<ComponentTypeId> &_types,
    bool _full) const
{
  // Set the default entity iterator to the end. This will allow us to know
  // if the entity has been added to the message.
  auto entIter = _msg.mutable_entities()->end();

  // Add an entity to the message and set it to be removed if the entity
  // exists in the toRemoveEntities list.
  if (this->dataPtr->toRemoveEntities.find(_entity) !=
      this->dataPtr->toRemoveEntities.end())
  {
    // Find the entity in the message, and add if not present.
    entIter = _msg.mutable_entities()->find(_entity);
    if (entIter == _msg.mutable_entities()->end())
    {
      msgs::SerializedEntityMap ent;
      ent.set_id(_entity);
      (*_msg.mutable_entities())[static_cast<uint64_t>(_entity)] = ent;
      entIter = _msg.mutable_entities()->find(_entity);
    }

    entIter->second.set_remove(true);
  }

  // Empty means all types
  bool allTypes = _types.empty();

  for (const ComponentKey &comp : this->dataPtr->entityComponents[_entity])
  {
    if (!allTypes && _types.find(comp.first) == _types.end())
    {
      continue;
    }

    const components::BaseComponent *compBase =
      this->ComponentImplementation(_entity, comp.first);

    // If not sending full state, skip unchanged components
    if (!_full &&
        this->dataPtr->oneTimeChangedComponents.find(comp) ==
        this->dataPtr->oneTimeChangedComponents.end() &&
        this->dataPtr->periodicChangedComponents.find(comp) ==
        this->dataPtr->periodicChangedComponents.end())
    {
      continue;
    }

    /// Find the entity in the message, if not already found.
    /// Add the entity to the message, if not already added.
    if (entIter == _msg.mutable_entities()->end())
    {
      entIter = _msg.mutable_entities()->find(_entity);
      if (entIter == _msg.mutable_entities()->end())
      {
        msgs::SerializedEntityMap ent;
        ent.set_id(_entity);
        (*_msg.mutable_entities())[static_cast<uint64_t>(_entity)] = ent;
        entIter = _msg.mutable_entities()->find(_entity);
      }
    }

    // Find the component in the message, and add the component to the
    // message if it's not present.
    auto compIter = entIter->second.mutable_components()->find(comp.first);
    if (compIter == entIter->second.mutable_components()->end())
    {
      msgs::SerializedComponent cmp;
      cmp.set_type(compBase->TypeId());
      (*(entIter->second.mutable_components()))[
        static_cast<int64_t>(comp.first)] = cmp;
      compIter = entIter->second.mutable_components()->find(comp.first);
    }

    // Serialize and store the message
    std::ostringstream ostr;
    compBase->Serialize(ostr);
    compIter->second.set_component(ostr.str());

    // TODO(anyone) Set component being removed once we have a way to queue it
  }

  // Remove the entity from the message if a component for the entity was
  // not modified or added. This will allow the state message to shrink.
  if (entIter == _msg.mutable_entities()->end() &&
      (entIter = _msg.mutable_entities()->find(_entity)) !=
      _msg.mutable_entities()->end())
  {
    _msg.mutable_entities()->erase(entIter);
  }
}

//////////////////////////////////////////////////
ignition::msgs::SerializedState EntityComponentManager::ChangedState() const
{
  ignition::msgs::SerializedState stateMsg;

  // New entities
  for (const auto &entity : this->dataPtr->newlyCreatedEntities)
  {
    this->AddEntityToMessage(stateMsg, entity);
  }

  // Entities being removed
  for (const auto &entity : this->dataPtr->toRemoveEntities)
  {
    this->AddEntityToMessage(stateMsg, entity);
  }

  // TODO(anyone) New / removed / changed components

  return stateMsg;
}

//////////////////////////////////////////////////
void EntityComponentManager::ChangedState(
    ignition::msgs::SerializedStateMap &_state) const
{
  // New entities
  for (const auto &entity : this->dataPtr->newlyCreatedEntities)
  {
    this->AddEntityToMessage(_state, entity);
  }

  // Entities being removed
  for (const auto &entity : this->dataPtr->toRemoveEntities)
  {
    this->AddEntityToMessage(_state, entity);
  }

  // TODO(anyone) New / removed / changed components
}


//////////////////////////////////////////////////
ignition::msgs::SerializedState EntityComponentManager::State(
    const std::unordered_set<Entity> &_entities,
    const std::unordered_set<ComponentTypeId> &_types) const
{
  ignition::msgs::SerializedState stateMsg;
  for (const auto &it : this->dataPtr->entityComponents)
  {
    auto entity = it.first;
    if (!_entities.empty() && _entities.find(entity) == _entities.end())
    {
      continue;
    }

    this->AddEntityToMessage(stateMsg, entity, _types);
  }

  return stateMsg;
}

//////////////////////////////////////////////////
void EntityComponentManager::State(
    msgs::SerializedStateMap  &_state,
    const std::unordered_set<Entity> &_entities,
    const std::unordered_set<ComponentTypeId> &_types,
    bool _full) const
{
  for (const auto &it : this->dataPtr->entityComponents)
  {
    if (_entities.empty() || _entities.find(it.first) != _entities.end())
      this->AddEntityToMessage(_state, it.first, _types, _full);
  }
}

//////////////////////////////////////////////////
void EntityComponentManager::SetState(
    const ignition::msgs::SerializedState &_stateMsg)
{
  IGN_PROFILE("EntityComponentManager::SetState Non-map");
  // Create / remove / update entities
  for (int e = 0; e < _stateMsg.entities_size(); ++e)
  {
    const auto &entityMsg = _stateMsg.entities(e);

    Entity entity{entityMsg.id()};

    // Remove entity
    if (entityMsg.remove())
    {
      this->RequestRemoveEntity(entity);
      continue;
    }

    // Create entity if it doesn't exist
    if (!this->HasEntity(entity))
    {
      this->dataPtr->CreateEntityImplementation(entity);
    }

    // Create / remove / update components
    for (int c = 0; c < entityMsg.components_size(); ++c)
    {
      const auto &compMsg = entityMsg.components(c);

      // Skip if component not set. Note that this will also skip components
      // setting an empty value.
      if (compMsg.component().empty())
      {
        continue;
      }

      auto type = compMsg.type();

      // Components which haven't been registered in this process, such as 3rd
      // party components streamed to other secondaries and the GUI.
      if (!components::Factory::Instance()->HasType(type))
      {
        static std::unordered_set<unsigned int> printedComps;
        if (printedComps.find(type) == printedComps.end())
        {
          printedComps.insert(type);
          ignwarn << "Component type [" << type << "] has not been "
                  << "registered in this process, so it can't be deserialized."
                  << std::endl;
        }
        continue;
      }

      // Create component
      auto newComp = components::Factory::Instance()->New(compMsg.type());

      if (nullptr == newComp)
      {
        ignerr << "Failed to deserialize component of type [" << compMsg.type()
               << "]" << std::endl;
        continue;
      }

      std::istringstream istr(compMsg.component());
      newComp->Deserialize(istr);

      // Get type id
      auto typeId = newComp->TypeId();

      // TODO(louise) Move into if, see TODO below
      this->RemoveComponent(entity, typeId);

      // Remove component
      if (compMsg.remove())
      {
        continue;
      }

      // Get Component
      auto comp = this->ComponentImplementation(entity, typeId);

      // Create if new
      if (nullptr == comp)
      {
        this->CreateComponentImplementation(entity, typeId, newComp.get());
      }
      // Update component value
      else
      {
        ignerr << "Internal error" << std::endl;
        // TODO(louise) We're shortcutting above and always  removing the
        // component so that we don't get here, gotta figure out why this
        // doesn't update the component. The following line prints the correct
        // values.
        // igndbg << *comp << "  " << *newComp.get() << std::endl;
        // *comp = *newComp.get();
      }
    }
  }
}

//////////////////////////////////////////////////
void EntityComponentManager::SetState(
    const ignition::msgs::SerializedStateMap &_stateMsg)
{
  IGN_PROFILE("EntityComponentManager::SetState Map");
  // Create / remove / update entities
  for (const auto &iter : _stateMsg.entities())
  {
    const auto &entityMsg = iter.second;

    Entity entity{entityMsg.id()};

    // Remove entity
    if (entityMsg.remove())
    {
      this->RequestRemoveEntity(entity);
      continue;
    }

    // Create entity if it doesn't exist
    if (!this->HasEntity(entity))
    {
      this->dataPtr->CreateEntityImplementation(entity);
    }

    // Create / remove / update components
    for (const auto &compIter : iter.second.components())
    {
      const auto &compMsg = compIter.second;

      // Skip if component not set. Note that this will also skip components
      // setting an empty value.
      if (compMsg.component().empty())
      {
        continue;
      }

      uint64_t type = compMsg.type();

      // Components which haven't been registered in this process, such as 3rd
      // party components streamed to other secondaries and the GUI.
      if (!components::Factory::Instance()->HasType(type))
      {
        static std::unordered_set<unsigned int> printedComps;
        if (printedComps.find(type) == printedComps.end())
        {
          printedComps.insert(type);
          ignwarn << "Component type [" << type << "] has not been "
                  << "registered in this process, so it can't be deserialized."
                  << std::endl;
        }
        continue;
      }

      // Remove component
      if (compMsg.remove())
      {
        this->RemoveComponent(entity, compIter.first);
        continue;
      }

      // Get Component
      components::BaseComponent *comp =
        this->ComponentImplementation(entity, compIter.first);

      // Create if new
      if (nullptr == comp)
      {
        // Create component
        auto newComp = components::Factory::Instance()->New(compMsg.type());

        if (nullptr == newComp)
        {
          ignerr << "Failed to create component of type [" << compMsg.type()
            << "]" << std::endl;
          continue;
        }

        std::istringstream istr(compMsg.component());
        newComp->Deserialize(istr);

        this->CreateComponentImplementation(entity,
            newComp->TypeId(), newComp.get());
      }
      // Update component value
      else
      {
        std::istringstream istr(compMsg.component());
        comp->Deserialize(istr);
        this->SetChanged(entity, compIter.first,
            ComponentState::OneTimeChange);
      }
    }
  }
}

//////////////////////////////////////////////////
std::unordered_set<Entity> EntityComponentManager::Descendants(Entity _entity)
    const
{
  // Check cache
  if (this->dataPtr->descendantCache.find(_entity) !=
      this->dataPtr->descendantCache.end())
  {
    return this->dataPtr->descendantCache[_entity];
  }

  std::unordered_set<Entity> descendants;

  if (!this->HasEntity(_entity))
    return descendants;

  auto descVector = math::graph::BreadthFirstSort(this->dataPtr->entities,
      _entity);
  std::move(descVector.begin(), descVector.end(), std::inserter(descendants,
      descendants.end()));

  this->dataPtr->descendantCache[_entity] = descendants;
  return descendants;
}

//////////////////////////////////////////////////
void EntityComponentManager::SetAllComponentsUnchanged()
{
  this->dataPtr->periodicChangedComponents.clear();
  this->dataPtr->oneTimeChangedComponents.clear();
}

/////////////////////////////////////////////////
void EntityComponentManager::SetChanged(
    const Entity _entity, const ComponentTypeId _type,
    gazebo::ComponentState _c)
{
  auto ecIter = this->dataPtr->entityComponents.find(_entity);

  if (ecIter == this->dataPtr->entityComponents.end())
    return;

  auto iter = std::find_if(ecIter->second.begin(), ecIter->second.end(),
        [&] (const ComponentKey &_key)
  {
    return _key.first == _type;
  });

  if (iter == ecIter->second.end())
    return;

  if (_c == ComponentState::PeriodicChange)
  {
    this->dataPtr->periodicChangedComponents.insert(*iter);
    this->dataPtr->oneTimeChangedComponents.erase(*iter);
  }
  else if (_c == ComponentState::OneTimeChange)
  {
    this->dataPtr->periodicChangedComponents.erase(*iter);
    this->dataPtr->oneTimeChangedComponents.insert(*iter);
  }
  else
  {
    this->dataPtr->periodicChangedComponents.erase(*iter);
    this->dataPtr->oneTimeChangedComponents.erase(*iter);
  }
}

/////////////////////////////////////////////////
std::unordered_set<ComponentTypeId> EntityComponentManager::ComponentTypes(
    const Entity _entity) const
{
  std::unordered_set<ComponentTypeId> result;

  auto it = this->dataPtr->entityComponents.find(_entity);
  if (it == this->dataPtr->entityComponents.end())
    return result;

  for (const auto &key : it->second)
  {
    result.insert(key.first);
  }

  return result;
}

/////////////////////////////////////////////////
void EntityComponentManager::SetEntityCreateOffset(uint64_t _offset)
{
  if (_offset < this->dataPtr->entityCount)
  {
    ignwarn << "Setting an entity offset of [" << _offset << "] is less than "
     << "the current entity count of [" << this->dataPtr->entityCount << "]. "
     << "Incorrect behavior should be expected.\n";
  }

  this->dataPtr->entityCount = _offset;
}