#include "objectpaging.hpp"

#include <unordered_map>
#include <vector>

#include <osg/LOD>
#include <osg/Material>
#include <osg/MatrixTransform>
#include <osg/Sequence>
#include <osg/Switch>
#include <osgAnimation/BasicAnimationManager>
#include <osgParticle/ParticleProcessor>
#include <osgParticle/ParticleSystemUpdater>
#include <osgUtil/IncrementalCompileOperation>

#include <components/esm3/esmreader.hpp>
#include <components/esm3/loadacti.hpp>
#include <components/esm3/loadcell.hpp>
#include <components/esm3/loadcont.hpp>
#include <components/esm3/loaddoor.hpp>
#include <components/esm3/loadstat.hpp>
#include <components/esm3/readerscache.hpp>
#include <components/misc/pathhelpers.hpp>
#include <components/misc/resourcehelpers.hpp>
#include <components/misc/rng.hpp>
#include <components/resource/scenemanager.hpp>
#include <components/sceneutil/lightmanager.hpp>
#include <components/sceneutil/morphgeometry.hpp>
#include <components/sceneutil/optimizer.hpp>
#include <components/sceneutil/positionattitudetransform.hpp>
#include <components/sceneutil/riggeometry.hpp>
#include <components/sceneutil/riggeometryosgaextension.hpp>
#include <components/sceneutil/util.hpp>
#include <components/settings/values.hpp>
#include <components/vfs/manager.hpp>

#include "apps/openmw/mwbase/environment.hpp"
#include "apps/openmw/mwbase/world.hpp"
#include "apps/openmw/mwworld/esmstore.hpp"

#include "vismask.hpp"

namespace MWRender
{
    namespace
    {
        bool typeFilter(int type, bool far)
        {
            switch (type)
            {
                case ESM::REC_STAT:
                case ESM::REC_ACTI:
                case ESM::REC_DOOR:
                    return true;
                case ESM::REC_CONT:
                    return !far;

                default:
                    return false;
            }
        }

        std::string getModel(int type, ESM::RefId id, const MWWorld::ESMStore& store)
        {
            switch (type)
            {
                case ESM::REC_STAT:
                    return store.get<ESM::Static>().searchStatic(id)->mModel;
                case ESM::REC_ACTI:
                    return store.get<ESM::Activator>().searchStatic(id)->mModel;
                case ESM::REC_DOOR:
                    return store.get<ESM::Door>().searchStatic(id)->mModel;
                case ESM::REC_CONT:
                    return store.get<ESM::Container>().searchStatic(id)->mModel;
                default:
                    return {};
            }
        }
    }

    osg::ref_ptr<osg::Node> ObjectPaging::getChunk(float size, const osg::Vec2f& center, unsigned char /*lod*/,
        unsigned int lodFlags, bool activeGrid, const osg::Vec3f& viewPoint, bool compile)
    {
        if (activeGrid && !mActiveGrid)
            return nullptr;

        const ChunkId id = std::make_tuple(center, size, activeGrid);

        if (const osg::ref_ptr<osg::Object> obj = mCache->getRefFromObjectCache(id))
            return static_cast<osg::Node*>(obj.get());

        const unsigned char lod = static_cast<unsigned char>(lodFlags >> (4 * 4));
        osg::ref_ptr<osg::Node> node = createChunk(size, center, activeGrid, viewPoint, compile, lod);
        mCache->addEntryToObjectCache(id, node.get());
        return node;
    }

    namespace
    {
        class CanOptimizeCallback : public SceneUtil::Optimizer::IsOperationPermissibleForObjectCallback
        {
        public:
            bool isOperationPermissibleForObjectImplementation(
                const SceneUtil::Optimizer* optimizer, const osg::Drawable* node, unsigned int option) const override
            {
                return true;
            }
            bool isOperationPermissibleForObjectImplementation(
                const SceneUtil::Optimizer* optimizer, const osg::Node* node, unsigned int option) const override
            {
                return (node->getDataVariance() != osg::Object::DYNAMIC);
            }
        };

        using LODRange = osg::LOD::MinMaxPair;

        LODRange intersection(const LODRange& left, const LODRange& right)
        {
            return { std::max(left.first, right.first), std::min(left.second, right.second) };
        }

        bool empty(const LODRange& r)
        {
            return r.first >= r.second;
        }

        LODRange operator/(const LODRange& r, float div)
        {
            return { r.first / div, r.second / div };
        }

        class CopyOp : public osg::CopyOp
        {
        public:
            bool mOptimizeBillboards = true;
            bool mActiveGrid = false;
            LODRange mDistances = { 0.f, 0.f };
            osg::Vec3f mViewVector;
            osg::Node::NodeMask mCopyMask = ~0u;
            mutable std::vector<const osg::Node*> mNodePath;

            CopyOp(bool activeGrid, osg::Node::NodeMask copyMask)
                : mActiveGrid(activeGrid)
                , mCopyMask(copyMask)
            {
            }

            void copy(const osg::Node* toCopy, osg::Group* attachTo)
            {
                const osg::Group* groupToCopy = toCopy->asGroup();
                if (toCopy->getStateSet() || toCopy->asTransform() || !groupToCopy)
                    attachTo->addChild(operator()(toCopy));
                else
                {
                    for (unsigned int i = 0; i < groupToCopy->getNumChildren(); ++i)
                        attachTo->addChild(operator()(groupToCopy->getChild(i)));
                }
            }

            osg::Node* operator()(const osg::Node* node) const override
            {
                if (!(node->getNodeMask() & mCopyMask))
                    return nullptr;

                if (const osg::Drawable* d = node->asDrawable())
                    return operator()(d);

                if (dynamic_cast<const osgParticle::ParticleProcessor*>(node))
                    return nullptr;
                if (dynamic_cast<const osgParticle::ParticleSystemUpdater*>(node))
                    return nullptr;

                if (const osg::Switch* sw = node->asSwitch())
                {
                    osg::Group* n = new osg::Group;
                    for (unsigned int i = 0; i < sw->getNumChildren(); ++i)
                        if (sw->getValue(i))
                            n->addChild(operator()(sw->getChild(i)));
                    n->setDataVariance(osg::Object::STATIC);
                    return n;
                }
                if (const osg::LOD* lod = dynamic_cast<const osg::LOD*>(node))
                {
                    std::vector<std::pair<osg::ref_ptr<osg::Node>, LODRange>> children;
                    for (unsigned int i = 0; i < lod->getNumChildren(); ++i)
                        if (const auto r = intersection(lod->getRangeList()[i], mDistances); !empty(r))
                            children.emplace_back(operator()(lod->getChild(i)), lod->getRangeList()[i]);
                    if (children.empty())
                        return nullptr;

                    if (children.size() == 1)
                        return children.front().first.release();
                    else
                    {
                        osg::LOD* n = new osg::LOD;
                        for (const auto& [child, range] : children)
                            n->addChild(child, range.first, range.second);
                        n->setDataVariance(osg::Object::STATIC);
                        return n;
                    }
                }
                if (const osg::Sequence* sq = dynamic_cast<const osg::Sequence*>(node))
                {
                    osg::Group* n = new osg::Group;
                    n->addChild(operator()(sq->getChild(sq->getValue() != -1 ? sq->getValue() : 0)));
                    n->setDataVariance(osg::Object::STATIC);
                    return n;
                }

                mNodePath.push_back(node);

                osg::Node* cloned = static_cast<osg::Node*>(node->clone(*this));
                if (!mActiveGrid)
                    cloned->setDataVariance(osg::Object::STATIC);
                cloned->setUserDataContainer(nullptr);
                cloned->setName("");

                mNodePath.pop_back();

                handleCallbacks(node, cloned);

                return cloned;
            }
            void handleCallbacks(const osg::Node* node, osg::Node* cloned) const
            {
                for (const osg::Callback* callback = node->getCullCallback(); callback != nullptr;
                     callback = callback->getNestedCallback())
                {
                    if (callback->className() == std::string("BillboardCallback"))
                    {
                        if (mOptimizeBillboards)
                        {
                            handleBillboard(cloned);
                            continue;
                        }
                        else
                            cloned->setDataVariance(osg::Object::DYNAMIC);
                    }

                    if (node->getCullCallback()->getNestedCallback())
                    {
                        osg::Callback* clonedCallback = osg::clone(callback, osg::CopyOp::SHALLOW_COPY);
                        clonedCallback->setNestedCallback(nullptr);
                        cloned->addCullCallback(clonedCallback);
                    }
                    else
                        cloned->addCullCallback(const_cast<osg::Callback*>(callback));
                }
            }
            void handleBillboard(osg::Node* node) const
            {
                osg::Transform* transform = node->asTransform();
                if (!transform)
                    return;
                osg::MatrixTransform* matrixTransform = transform->asMatrixTransform();
                if (!matrixTransform)
                    return;

                osg::Matrix worldToLocal = osg::Matrix::identity();
                for (auto pathNode : mNodePath)
                    if (const osg::Transform* t = pathNode->asTransform())
                        t->computeWorldToLocalMatrix(worldToLocal, nullptr);
                worldToLocal = osg::Matrix::orthoNormal(worldToLocal);

                osg::Matrix billboardMatrix;
                osg::Vec3f viewVector = -(mViewVector + worldToLocal.getTrans());
                viewVector.normalize();
                osg::Vec3f right = viewVector ^ osg::Vec3f(0, 0, 1);
                right.normalize();
                osg::Vec3f up = right ^ viewVector;
                up.normalize();
                billboardMatrix.makeLookAt(osg::Vec3f(0, 0, 0), viewVector, up);
                billboardMatrix.invert(billboardMatrix);

                const osg::Matrix& oldMatrix = matrixTransform->getMatrix();
                float mag[3]; // attempt to preserve scale
                for (int i = 0; i < 3; ++i)
                    mag[i] = std::sqrt(oldMatrix(0, i) * oldMatrix(0, i) + oldMatrix(1, i) * oldMatrix(1, i)
                        + oldMatrix(2, i) * oldMatrix(2, i));
                osg::Matrix newMatrix;
                worldToLocal.setTrans(0, 0, 0);
                newMatrix *= worldToLocal;
                newMatrix.preMult(billboardMatrix);
                newMatrix.preMultScale(osg::Vec3f(mag[0], mag[1], mag[2]));
                newMatrix.setTrans(oldMatrix.getTrans());

                matrixTransform->setMatrix(newMatrix);
            }
            osg::Drawable* operator()(const osg::Drawable* drawable) const override
            {
                if (!(drawable->getNodeMask() & mCopyMask))
                    return nullptr;

                if (dynamic_cast<const osgParticle::ParticleSystem*>(drawable))
                    return nullptr;

                if (dynamic_cast<const SceneUtil::OsgaRigGeometry*>(drawable))
                    return nullptr;
                if (const SceneUtil::RigGeometry* rig = dynamic_cast<const SceneUtil::RigGeometry*>(drawable))
                    return operator()(rig->getSourceGeometry());
                if (const SceneUtil::MorphGeometry* morph = dynamic_cast<const SceneUtil::MorphGeometry*>(drawable))
                    return operator()(morph->getSourceGeometry());

                if (getCopyFlags() & DEEP_COPY_DRAWABLES)
                {
                    osg::Drawable* d = static_cast<osg::Drawable*>(drawable->clone(*this));
                    d->setDataVariance(osg::Object::STATIC);
                    d->setUserDataContainer(nullptr);
                    d->setName("");
                    return d;
                }
                else
                    return const_cast<osg::Drawable*>(drawable);
            }
            osg::Callback* operator()(const osg::Callback* callback) const override { return nullptr; }
        };

        class RefnumSet : public osg::Object
        {
        public:
            RefnumSet() {}
            RefnumSet(const RefnumSet& copy, const osg::CopyOp&)
                : mRefnums(copy.mRefnums)
            {
            }
            META_Object(MWRender, RefnumSet)
            std::vector<ESM::RefNum> mRefnums;
        };

        class AnalyzeVisitor : public osg::NodeVisitor
        {
        public:
            AnalyzeVisitor(osg::Node::NodeMask analyzeMask)
                : osg::NodeVisitor(TRAVERSE_ALL_CHILDREN)
                , mCurrentStateSet(nullptr)
            {
                setTraversalMask(analyzeMask);
            }

            typedef std::unordered_map<osg::StateSet*, unsigned int> StateSetCounter;
            struct Result
            {
                StateSetCounter mStateSetCounter;
                unsigned int mNumVerts = 0;
            };

            void apply(osg::Node& node) override
            {
                if (node.getStateSet())
                    mCurrentStateSet = node.getStateSet();

                if (osg::Switch* sw = node.asSwitch())
                {
                    for (unsigned int i = 0; i < sw->getNumChildren(); ++i)
                        if (sw->getValue(i))
                            traverse(*sw->getChild(i));
                    return;
                }
                if (osg::LOD* lod = dynamic_cast<osg::LOD*>(&node))
                {
                    for (unsigned int i = 0; i < lod->getNumChildren(); ++i)
                        if (const auto r = intersection(lod->getRangeList()[i], mDistances); !empty(r))
                            traverse(*lod->getChild(i));
                    return;
                }
                if (osg::Sequence* sq = dynamic_cast<osg::Sequence*>(&node))
                {
                    traverse(*sq->getChild(sq->getValue() != -1 ? sq->getValue() : 0));
                    return;
                }

                traverse(node);
            }
            void apply(osg::Geometry& geom) override
            {
                if (osg::Array* array = geom.getVertexArray())
                    mResult.mNumVerts += array->getNumElements();

                ++mResult.mStateSetCounter[mCurrentStateSet];
                ++mGlobalStateSetCounter[mCurrentStateSet];
            }
            Result retrieveResult()
            {
                Result result = mResult;
                mResult = Result();
                mCurrentStateSet = nullptr;
                return result;
            }
            void addInstance(const Result& result)
            {
                for (auto pair : result.mStateSetCounter)
                    mGlobalStateSetCounter[pair.first] += pair.second;
            }
            float getMergeBenefit(const Result& result)
            {
                if (result.mStateSetCounter.empty())
                    return 1;
                float mergeBenefit = 0;
                for (auto pair : result.mStateSetCounter)
                {
                    mergeBenefit += mGlobalStateSetCounter[pair.first];
                }
                mergeBenefit /= result.mStateSetCounter.size();
                return mergeBenefit;
            }

            Result mResult;
            osg::StateSet* mCurrentStateSet;
            StateSetCounter mGlobalStateSetCounter;
            LODRange mDistances = { 0.f, 0.f };
        };

        class DebugVisitor : public osg::NodeVisitor
        {
        public:
            DebugVisitor()
                : osg::NodeVisitor(TRAVERSE_ALL_CHILDREN)
            {
            }
            void apply(osg::Drawable& node) override
            {
                osg::ref_ptr<osg::Material> m(new osg::Material);
                osg::Vec4f color(
                    Misc::Rng::rollProbability(), Misc::Rng::rollProbability(), Misc::Rng::rollProbability(), 0.f);
                color.normalize();
                m->setDiffuse(osg::Material::FRONT_AND_BACK, osg::Vec4f(0.1f, 0.1f, 0.1f, 1.f));
                m->setAmbient(osg::Material::FRONT_AND_BACK, osg::Vec4f(0.1f, 0.1f, 0.1f, 1.f));
                m->setColorMode(osg::Material::OFF);
                m->setEmission(osg::Material::FRONT_AND_BACK, osg::Vec4f(color));
                osg::ref_ptr<osg::StateSet> stateset = node.getStateSet()
                    ? osg::clone(node.getStateSet(), osg::CopyOp::SHALLOW_COPY)
                    : new osg::StateSet;
                stateset->setAttribute(m);
                stateset->addUniform(new osg::Uniform("colorMode", 0));
                stateset->addUniform(new osg::Uniform("emissiveMult", 1.f));
                stateset->addUniform(new osg::Uniform("specStrength", 1.f));
                node.setStateSet(stateset);
            }
        };

        class AddRefnumMarkerVisitor : public osg::NodeVisitor
        {
        public:
            AddRefnumMarkerVisitor(ESM::RefNum refnum)
                : osg::NodeVisitor(TRAVERSE_ALL_CHILDREN)
                , mRefnum(refnum)
            {
            }
            ESM::RefNum mRefnum;
            void apply(osg::Geometry& node) override
            {
                osg::ref_ptr<RefnumMarker> marker(new RefnumMarker);
                marker->mRefnum = mRefnum;
                if (osg::Array* array = node.getVertexArray())
                    marker->mNumVertices = array->getNumElements();
                node.getOrCreateUserDataContainer()->addUserObject(marker);
            }
        };
    }

    ObjectPaging::ObjectPaging(Resource::SceneManager* sceneManager, ESM::RefId worldspace)
        : GenericResourceManager<ChunkId>(nullptr, Settings::cells().mCacheExpiryDelay)
        , Terrain::QuadTreeWorld::ChunkManager(worldspace)
        , mSceneManager(sceneManager)
        , mActiveGrid(Settings::terrain().mObjectPagingActiveGrid)
        , mDebugBatches(Settings::terrain().mDebugChunks)
        , mMergeFactor(Settings::terrain().mObjectPagingMergeFactor)
        , mMinSize(Settings::terrain().mObjectPagingMinSize)
        , mMinSizeMergeFactor(Settings::terrain().mObjectPagingMinSizeMergeFactor)
        , mMinSizeCostMultiplier(Settings::terrain().mObjectPagingMinSizeCostMultiplier)
        , mRefTrackerLocked(false)
    {
    }

    namespace
    {
        struct PagedCellRef
        {
            ESM::RefId mRefId;
            ESM::RefNum mRefNum;
            osg::Vec3f mPosition;
            osg::Vec3f mRotation;
            float mScale;
        };

        PagedCellRef makePagedCellRef(const ESM::CellRef& value)
        {
            return PagedCellRef{
                .mRefId = value.mRefID,
                .mRefNum = value.mRefNum,
                .mPosition = value.mPos.asVec3(),
                .mRotation = value.mPos.asRotationVec3(),
                .mScale = value.mScale,
            };
        }

        std::map<ESM::RefNum, PagedCellRef> collectESM3References(
            float size, const osg::Vec2i& startCell, const MWWorld::ESMStore& store)
        {
            std::map<ESM::RefNum, PagedCellRef> refs;
            ESM::ReadersCache readers;
            for (int cellX = startCell.x(); cellX < startCell.x() + size; ++cellX)
            {
                for (int cellY = startCell.y(); cellY < startCell.y() + size; ++cellY)
                {
                    const ESM::Cell* cell = store.get<ESM::Cell>().searchStatic(cellX, cellY);
                    if (!cell)
                        continue;
                    for (size_t i = 0; i < cell->mContextList.size(); ++i)
                    {
                        try
                        {
                            const std::size_t index = static_cast<std::size_t>(cell->mContextList[i].index);
                            const ESM::ReadersCache::BusyItem reader = readers.get(index);
                            cell->restore(*reader, i);
                            ESM::CellRef ref;
                            ESM::MovedCellRef cMRef;
                            bool deleted = false;
                            bool moved = false;
                            while (ESM::Cell::getNextRef(
                                *reader, ref, deleted, cMRef, moved, ESM::Cell::GetNextRefMode::LoadOnlyNotMoved))
                            {
                                if (moved)
                                    continue;

                                if (std::find(cell->mMovedRefs.begin(), cell->mMovedRefs.end(), ref.mRefNum)
                                    != cell->mMovedRefs.end())
                                    continue;

                                int type = store.findStatic(ref.mRefID);
                                if (!typeFilter(type, size >= 2))
                                    continue;
                                if (deleted)
                                {
                                    refs.erase(ref.mRefNum);
                                    continue;
                                }
                                refs.insert_or_assign(ref.mRefNum, makePagedCellRef(ref));
                            }
                        }
                        catch (const std::exception& e)
                        {
                            Log(Debug::Warning) << "Failed to collect references from cell \"" << cell->getDescription()
                                                << "\": " << e.what();
                            continue;
                        }
                    }
                    for (const auto& [ref, deleted] : cell->mLeasedRefs)
                    {
                        if (deleted)
                        {
                            refs.erase(ref.mRefNum);
                            continue;
                        }
                        int type = store.findStatic(ref.mRefID);
                        if (!typeFilter(type, size >= 2))
                            continue;
                        refs.insert_or_assign(ref.mRefNum, makePagedCellRef(ref));
                    }
                }
            }
            return refs;
        }
    }

    osg::ref_ptr<osg::Node> ObjectPaging::createChunk(float size, const osg::Vec2f& center, bool activeGrid,
        const osg::Vec3f& viewPoint, bool compile, unsigned char lod)
    {
        const osg::Vec2i startCell(std::floor(center.x() - size / 2.f), std::floor(center.y() - size / 2.f));
        const MWBase::World& world = *MWBase::Environment::get().getWorld();
        const MWWorld::ESMStore& store = world.getStore();

        std::map<ESM::RefNum, PagedCellRef> refs;

        if (mWorldspace == ESM::Cell::sDefaultWorldspaceId)
        {
            refs = collectESM3References(size, startCell, store);
        }
        else
        {
            // TODO
        }

        if (activeGrid && !refs.empty())
        {
            std::lock_guard<std::mutex> lock(mRefTrackerMutex);
            const std::set<ESM::RefNum>& blacklist = getRefTracker().mBlacklist;
            if (blacklist.size() < refs.size())
            {
                for (ESM::RefNum ref : blacklist)
                    refs.erase(ref);
            }
            else
            {
                std::erase_if(refs, [&](const auto& ref) { return blacklist.contains(ref.first); });
            }
        }

        const osg::Vec2f minBound = (center - osg::Vec2f(size / 2.f, size / 2.f));
        const osg::Vec2f maxBound = (center + osg::Vec2f(size / 2.f, size / 2.f));
        const osg::Vec2i floorMinBound(std::floor(minBound.x()), std::floor(minBound.y()));
        const osg::Vec2i ceilMaxBound(std::ceil(maxBound.x()), std::ceil(maxBound.y()));
        struct InstanceList
        {
            std::vector<const PagedCellRef*> mInstances;
            AnalyzeVisitor::Result mAnalyzeResult;
            bool mNeedCompile = false;
        };
        typedef std::map<osg::ref_ptr<const osg::Node>, InstanceList> NodeMap;
        NodeMap nodes;
        const osg::ref_ptr<RefnumSet> refnumSet = activeGrid ? new RefnumSet : nullptr;

        // Mask_UpdateVisitor is used in such cases in NIF loader:
        // 1. For collision nodes, which is not supposed to be rendered.
        // 2. For nodes masked via Flag_Hidden (VisController can change this flag value at runtime).
        // Since ObjectPaging does not handle VisController, we can just ignore both types of nodes.
        constexpr auto copyMask = ~Mask_UpdateVisitor;

        const int cellSize = getCellSize(mWorldspace);
        const float smallestDistanceToChunk = (size > 1 / 8.f) ? (size * cellSize) : 0.f;
        const float higherDistanceToChunk
            = activeGrid ? ((size < 1) ? 5 : 3) * cellSize * size + 1 : smallestDistanceToChunk + 1;

        AnalyzeVisitor analyzeVisitor(copyMask);
        const float minSize = mMinSizeMergeFactor ? mMinSize * mMinSizeMergeFactor : mMinSize;
        for (const auto& [refNum, ref] : refs)
        {
            if (size < 1.f)
            {
                const osg::Vec3f cellPos = ref.mPosition / cellSize;
                if ((minBound.x() > floorMinBound.x() && cellPos.x() < minBound.x())
                    || (minBound.y() > floorMinBound.y() && cellPos.y() < minBound.y())
                    || (maxBound.x() < ceilMaxBound.x() && cellPos.x() >= maxBound.x())
                    || (maxBound.y() < ceilMaxBound.y() && cellPos.y() >= maxBound.y()))
                    continue;
            }

            const float dSqr = (viewPoint - ref.mPosition).length2();
            if (!activeGrid)
            {
                std::lock_guard<std::mutex> lock(mSizeCacheMutex);
                SizeCache::iterator found = mSizeCache.find(refNum);
                if (found != mSizeCache.end() && found->second < dSqr * minSize * minSize)
                    continue;
            }

            if (Misc::ResourceHelpers::isHiddenMarker(ref.mRefId))
                continue;

            const int type = store.findStatic(ref.mRefId);
            VFS::Path::Normalized model = getModel(type, ref.mRefId, store);
            if (model.empty())
                continue;
            model = Misc::ResourceHelpers::correctMeshPath(model);

            if (activeGrid && type != ESM::REC_STAT)
            {
                model = Misc::ResourceHelpers::correctActorModelPath(model, mSceneManager->getVFS());
                if (Misc::getFileExtension(model) == "nif")
                {
                    VFS::Path::Normalized kfname = model;
                    kfname.changeExtension("kf");
                    if (mSceneManager->getVFS()->exists(kfname))
                        continue;
                }
            }

            if (!activeGrid)
            {
                std::lock_guard<std::mutex> lock(mLODNameCacheMutex);
                LODNameCacheKey key{ model, lod };
                LODNameCache::const_iterator found = mLODNameCache.lower_bound(key);
                if (found != mLODNameCache.end() && found->first == key)
                    model = found->second;
                else
                    model = mLODNameCache
                                .emplace_hint(found, std::move(key),
                                    Misc::ResourceHelpers::getLODMeshName(world.getESMVersions()[refNum.mContentFile],
                                        model, *mSceneManager->getVFS(), lod))
                                ->second;
            }

            osg::ref_ptr<const osg::Node> cnode = mSceneManager->getTemplate(model, false);

            if (activeGrid)
            {
                if (cnode->getNumChildrenRequiringUpdateTraversal() > 0
                    || SceneUtil::hasUserDescription(cnode, Constants::NightDayLabel)
                    || SceneUtil::hasUserDescription(cnode, Constants::HerbalismLabel)
                    || (cnode->getName() == "Collada visual scene group"
                        && dynamic_cast<const osgAnimation::BasicAnimationManager*>(cnode->getUpdateCallback())))
                    continue;
                else
                    refnumSet->mRefnums.push_back(refNum);
            }

            {
                std::lock_guard<std::mutex> lock(mRefTrackerMutex);
                if (getRefTracker().mDisabled.count(refNum))
                    continue;
            }

            const float radius2 = cnode->getBound().radius2() * ref.mScale * ref.mScale;
            if (radius2 < dSqr * minSize * minSize && !activeGrid)
            {
                std::lock_guard<std::mutex> lock(mSizeCacheMutex);
                mSizeCache[refNum] = radius2;
                continue;
            }

            const auto emplaced = nodes.emplace(std::move(cnode), InstanceList());
            if (emplaced.second)
            {
                analyzeVisitor.mDistances = LODRange{ smallestDistanceToChunk, higherDistanceToChunk } / ref.mScale;
                const osg::Node* const nodePtr = emplaced.first->first.get();
                // const-trickery required because there is no const version of NodeVisitor
                const_cast<osg::Node*>(nodePtr)->accept(analyzeVisitor);
                emplaced.first->second.mAnalyzeResult = analyzeVisitor.retrieveResult();
                emplaced.first->second.mNeedCompile = compile && nodePtr->referenceCount() <= 2;
            }
            else
                analyzeVisitor.addInstance(emplaced.first->second.mAnalyzeResult);
            emplaced.first->second.mInstances.push_back(&ref);
        }

        const osg::Vec3f worldCenter = osg::Vec3f(center.x(), center.y(), 0) * getCellSize(mWorldspace);
        osg::ref_ptr<osg::Group> group = new osg::Group;
        osg::ref_ptr<osg::Group> mergeGroup = new osg::Group;
        osg::ref_ptr<Resource::TemplateMultiRef> templateRefs = new Resource::TemplateMultiRef;
        osgUtil::StateToCompile stateToCompile(0, nullptr);
        CopyOp copyop(activeGrid, copyMask);
        for (const auto& pair : nodes)
        {
            const osg::Node* cnode = pair.first;

            const AnalyzeVisitor::Result& analyzeResult = pair.second.mAnalyzeResult;

            const float mergeCost = analyzeResult.mNumVerts * size;
            const float mergeBenefit = analyzeVisitor.getMergeBenefit(analyzeResult) * mMergeFactor;
            const bool merge = mergeBenefit > mergeCost;

            const float factor2
                = mergeBenefit > 0 ? std::min(1.f, mergeCost * mMinSizeCostMultiplier / mergeBenefit) : 1;
            const float minSizeMergeFactor2 = (1 - factor2) * mMinSizeMergeFactor + factor2;
            const float minSizeMerged = minSizeMergeFactor2 > 0 ? mMinSize * minSizeMergeFactor2 : mMinSize;

            unsigned int numinstances = 0;
            for (const PagedCellRef* refPtr : pair.second.mInstances)
            {
                const PagedCellRef& ref = *refPtr;

                if (!activeGrid && minSizeMerged != minSize
                    && cnode->getBound().radius2() * ref.mScale * ref.mScale
                        < (viewPoint - ref.mPosition).length2() * minSizeMerged * minSizeMerged)
                    continue;

                const osg::Vec3f nodePos = ref.mPosition - worldCenter;
                const osg::Quat nodeAttitude = osg::Quat(ref.mRotation.z(), osg::Vec3f(0, 0, -1))
                    * osg::Quat(ref.mRotation.y(), osg::Vec3f(0, -1, 0))
                    * osg::Quat(ref.mRotation.x(), osg::Vec3f(-1, 0, 0));
                const osg::Vec3f nodeScale(ref.mScale, ref.mScale, ref.mScale);

                osg::ref_ptr<osg::Group> trans;
                if (merge)
                {
                    // Optimizer currently supports only MatrixTransforms.
                    osg::Matrixf matrix;
                    matrix.preMultTranslate(nodePos);
                    matrix.preMultRotate(nodeAttitude);
                    matrix.preMultScale(nodeScale);
                    trans = new osg::MatrixTransform(matrix);
                    trans->setDataVariance(osg::Object::STATIC);
                }
                else
                {
                    trans = new SceneUtil::PositionAttitudeTransform;
                    SceneUtil::PositionAttitudeTransform* pat
                        = static_cast<SceneUtil::PositionAttitudeTransform*>(trans.get());
                    pat->setPosition(nodePos);
                    pat->setScale(nodeScale);
                    pat->setAttitude(nodeAttitude);
                }

                // DO NOT COPY AND PASTE THIS CODE. Cloning osg::Geometry without also cloning its contained Arrays is
                // generally unsafe. In this specific case the operation is safe under the following two assumptions:
                // - When Arrays are removed or replaced in the cloned geometry, the original Arrays in their place must
                // outlive the cloned geometry regardless. (ensured by TemplateMultiRef)
                // - Arrays that we add or replace in the cloned geometry must be explicitely forbidden from reusing
                // BufferObjects of the original geometry. (ensured by needvbo() in optimizer.cpp)
                copyop.setCopyFlags(merge ? osg::CopyOp::DEEP_COPY_NODES | osg::CopyOp::DEEP_COPY_DRAWABLES
                                          : osg::CopyOp::DEEP_COPY_NODES);
                copyop.mOptimizeBillboards = (size > 1 / 4.f);
                copyop.mNodePath.push_back(trans);
                copyop.mDistances = LODRange{ smallestDistanceToChunk, higherDistanceToChunk } / ref.mScale;
                copyop.mViewVector = (viewPoint - worldCenter);
                copyop.copy(cnode, trans);
                copyop.mNodePath.pop_back();

                if (activeGrid)
                {
                    if (merge)
                    {
                        AddRefnumMarkerVisitor visitor(ref.mRefNum);
                        trans->accept(visitor);
                    }
                    else
                    {
                        osg::ref_ptr<RefnumMarker> marker = new RefnumMarker;
                        marker->mRefnum = ref.mRefNum;
                        trans->getOrCreateUserDataContainer()->addUserObject(marker);
                    }
                }

                osg::Group* const attachTo = merge ? mergeGroup : group;
                attachTo->addChild(trans);
                ++numinstances;
            }
            if (numinstances > 0)
            {
                // add a ref to the original template to help verify the safety of shallow cloning operations
                // in addition, we hint to the cache that it's still being used and should be kept in cache
                templateRefs->addRef(cnode);

                if (pair.second.mNeedCompile)
                {
                    int mode = osgUtil::GLObjectsVisitor::COMPILE_STATE_ATTRIBUTES;
                    if (!merge)
                        mode |= osgUtil::GLObjectsVisitor::COMPILE_DISPLAY_LISTS;
                    stateToCompile._mode = mode;
                    const_cast<osg::Node*>(cnode)->accept(stateToCompile);
                }
            }
        }

        const osg::Vec3f relativeViewPoint = viewPoint - worldCenter;

        if (mergeGroup->getNumChildren())
        {
            SceneUtil::Optimizer optimizer;
            if (size > 1 / 8.f)
            {
                optimizer.setViewPoint(relativeViewPoint);
                optimizer.setMergeAlphaBlending(true);
            }
            optimizer.setIsOperationPermissibleForObjectCallback(new CanOptimizeCallback);
            const unsigned int options = SceneUtil::Optimizer::FLATTEN_STATIC_TRANSFORMS
                | SceneUtil::Optimizer::REMOVE_REDUNDANT_NODES | SceneUtil::Optimizer::MERGE_GEOMETRY;

            optimizer.optimize(mergeGroup, options);

            group->addChild(mergeGroup);

            if (mDebugBatches)
            {
                DebugVisitor dv;
                mergeGroup->accept(dv);
            }
            if (compile)
            {
                stateToCompile._mode = osgUtil::GLObjectsVisitor::COMPILE_DISPLAY_LISTS;
                mergeGroup->accept(stateToCompile);
            }
        }

        osgUtil::IncrementalCompileOperation* const ico = mSceneManager->getIncrementalCompileOperation();
        if (!stateToCompile.empty() && ico)
        {
            auto compileSet = new osgUtil::IncrementalCompileOperation::CompileSet(group);
            compileSet->buildCompileMap(ico->getContextSet(), stateToCompile);
            ico->add(compileSet, false);
        }

        group->getBound();
        group->setNodeMask(Mask_Static);
        osg::UserDataContainer* udc = group->getOrCreateUserDataContainer();
        if (activeGrid)
        {
            std::sort(refnumSet->mRefnums.begin(), refnumSet->mRefnums.end());
            refnumSet->mRefnums.erase(
                std::unique(refnumSet->mRefnums.begin(), refnumSet->mRefnums.end()), refnumSet->mRefnums.end());
            udc->addUserObject(refnumSet);
            group->addCullCallback(new SceneUtil::LightListCallback);
        }
        udc->addUserObject(templateRefs);

        return group;
    }

    unsigned int ObjectPaging::getNodeMask()
    {
        return Mask_Static;
    }

    namespace
    {
        osg::Vec2f clampToCell(const osg::Vec3f& cellPos, const osg::Vec2i& cell)
        {
            return osg::Vec2f(std::clamp<float>(cellPos.x(), cell.x(), cell.x() + 1),
                std::clamp<float>(cellPos.y(), cell.y(), cell.y() + 1));
        }

        class CollectIntersecting
        {
        public:
            explicit CollectIntersecting(
                bool activeGridOnly, const osg::Vec3f& position, const osg::Vec2i& cell, ESM::RefId worldspace)
                : mActiveGridOnly(activeGridOnly)
                , mPosition(clampToCell(position / getCellSize(worldspace), cell))
            {
            }

            void operator()(const ChunkId& id, osg::Object* /*obj*/)
            {
                if (mActiveGridOnly && !std::get<2>(id))
                    return;
                if (intersects(id))
                    mCollected.push_back(id);
            }

            const std::vector<ChunkId>& getCollected() const { return mCollected; }

        private:
            bool intersects(ChunkId id) const
            {
                const osg::Vec2f center = std::get<0>(id);
                const float halfSize = std::get<1>(id) / 2;
                return mPosition.x() >= center.x() - halfSize && mPosition.y() >= center.y() - halfSize
                    && mPosition.x() <= center.x() + halfSize && mPosition.y() <= center.y() + halfSize;
            }

            bool mActiveGridOnly;
            osg::Vec2f mPosition;
            std::vector<ChunkId> mCollected;
        };
    }

    bool ObjectPaging::enableObject(
        int type, ESM::RefNum refnum, const osg::Vec3f& pos, const osg::Vec2i& cell, bool enabled)
    {
        if (!typeFilter(type, false))
            return false;

        {
            std::lock_guard<std::mutex> lock(mRefTrackerMutex);
            if (enabled && !getWritableRefTracker().mDisabled.erase(refnum))
                return false;
            if (!enabled && !getWritableRefTracker().mDisabled.insert(refnum).second)
                return false;
            if (mRefTrackerLocked)
                return false;
        }

        CollectIntersecting ccf(false, pos, cell, mWorldspace);
        mCache->call(ccf);
        if (ccf.getCollected().empty())
            return false;
        for (const ChunkId& chunk : ccf.getCollected())
            mCache->removeFromObjectCache(chunk);
        return true;
    }

    bool ObjectPaging::blacklistObject(int type, ESM::RefNum refnum, const osg::Vec3f& pos, const osg::Vec2i& cell)
    {
        if (!typeFilter(type, false))
            return false;

        {
            std::lock_guard<std::mutex> lock(mRefTrackerMutex);
            if (!getWritableRefTracker().mBlacklist.insert(refnum).second)
                return false;
            if (mRefTrackerLocked)
                return false;
        }

        CollectIntersecting ccf(true, pos, cell, mWorldspace);
        mCache->call(ccf);
        if (ccf.getCollected().empty())
            return false;
        for (const ChunkId& chunk : ccf.getCollected())
            mCache->removeFromObjectCache(chunk);
        return true;
    }

    void ObjectPaging::clear()
    {
        std::lock_guard<std::mutex> lock(mRefTrackerMutex);
        mRefTrackerNew.mDisabled.clear();
        mRefTrackerNew.mBlacklist.clear();
        mRefTrackerLocked = true;
    }

    bool ObjectPaging::unlockCache()
    {
        if (!mRefTrackerLocked)
            return false;
        {
            std::lock_guard<std::mutex> lock(mRefTrackerMutex);
            mRefTrackerLocked = false;
            if (mRefTracker == mRefTrackerNew)
                return false;
            else
                mRefTracker = mRefTrackerNew;
        }
        mCache->clear();
        return true;
    }

    namespace
    {
        struct GetRefnumsFunctor
        {
            GetRefnumsFunctor(std::vector<ESM::RefNum>& output)
                : mOutput(output)
            {
            }
            void operator()(MWRender::ChunkId chunkId, osg::Object* obj)
            {
                if (!std::get<2>(chunkId))
                    return;
                const osg::Vec2f& center = std::get<0>(chunkId);
                const bool activeGrid = (center.x() > mActiveGrid.x() || center.y() > mActiveGrid.y()
                    || center.x() < mActiveGrid.z() || center.y() < mActiveGrid.w());
                if (!activeGrid)
                    return;

                osg::UserDataContainer* udc = obj->getUserDataContainer();
                if (udc && udc->getNumUserObjects())
                {
                    RefnumSet* refnums = dynamic_cast<RefnumSet*>(udc->getUserObject(0));
                    if (!refnums)
                        return;
                    mOutput.insert(mOutput.end(), refnums->mRefnums.begin(), refnums->mRefnums.end());
                }
            }
            osg::Vec4i mActiveGrid;
            std::vector<ESM::RefNum>& mOutput;
        };
    }

    void ObjectPaging::getPagedRefnums(const osg::Vec4i& activeGrid, std::vector<ESM::RefNum>& out)
    {
        GetRefnumsFunctor grf(out);
        grf.mActiveGrid = activeGrid;
        mCache->call(grf);
        std::sort(out.begin(), out.end());
        out.erase(std::unique(out.begin(), out.end()), out.end());
    }

    void ObjectPaging::reportStats(unsigned int frameNumber, osg::Stats* stats) const
    {
        Resource::reportStats("Object Chunk", frameNumber, mCache->getStats(), *stats);
    }

}
