/*
Open Asset Import Library (assimp)
----------------------------------------------------------------------

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All rights reserved.

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  copyright notice, this list of conditions and the
  following disclaimer.

* Redistributions in binary form must reproduce the above
  copyright notice, this list of conditions and the
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"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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*/

/** @file  IFCLoad.cpp
 *  @brief Implementation of the Industry Foundation Classes loader.
 */

#ifndef ASSIMP_BUILD_NO_IFC_IMPORTER

#include <iterator>
#include <limits>
#include <tuple>

#ifndef ASSIMP_BUILD_NO_COMPRESSED_IFC
#ifdef ASSIMP_USE_HUNTER
#include <minizip/unzip.h>
#else
#include <unzip.h>
#endif
#endif

#include "../STEPParser/STEPFileReader.h"
#include "IFCLoader.h"

#include "IFCUtil.h"

#include <assimp/MemoryIOWrapper.h>
#include <assimp/importerdesc.h>
#include <assimp/scene.h>
#include <assimp/Importer.hpp>

namespace Assimp {
template <>
const char *LogFunctions<IFCImporter>::Prefix() {
    static auto prefix = "IFC: ";
    return prefix;
}
} // namespace Assimp

using namespace Assimp;
using namespace Assimp::Formatter;
using namespace Assimp::IFC;

/* DO NOT REMOVE this comment block. The genentitylist.sh script
 * just looks for names adhering to the IfcSomething naming scheme
 * and includes all matches in the whitelist for code-generation. Thus,
 * all entity classes that are only indirectly referenced need to be
 * mentioned explicitly.

  IfcRepresentationMap
  IfcProductRepresentation
  IfcUnitAssignment
  IfcClosedShell
  IfcDoor

 */

namespace {

// forward declarations
void SetUnits(ConversionData &conv);
void SetCoordinateSpace(ConversionData &conv);
void ProcessSpatialStructures(ConversionData &conv);
void MakeTreeRelative(ConversionData &conv);
void ConvertUnit(const ::Assimp::STEP::EXPRESS::DataType &dt, ConversionData &conv);

} // namespace

static const aiImporterDesc desc = {
    "Industry Foundation Classes (IFC) Importer",
    "",
    "",
    "",
    aiImporterFlags_SupportBinaryFlavour,
    0,
    0,
    0,
    0,
    "ifc ifczip step stp"
};

// ------------------------------------------------------------------------------------------------
// Constructor to be privately used by Importer
IFCImporter::IFCImporter() {}

// ------------------------------------------------------------------------------------------------
// Destructor, private as well
IFCImporter::~IFCImporter() {
}

// ------------------------------------------------------------------------------------------------
// Returns whether the class can handle the format of the given file.
bool IFCImporter::CanRead(const std::string &pFile, IOSystem *pIOHandler, bool checkSig) const {
    const std::string &extension = GetExtension(pFile);
    if (extension == "ifc" || extension == "ifczip") {
        return true;
    } else if ((!extension.length() || checkSig) && pIOHandler) {
        // note: this is the common identification for STEP-encoded files, so
        // it is only unambiguous as long as we don't support any further
        // file formats with STEP as their encoding.
        const char *tokens[] = { "ISO-10303-21" };
        const bool found(SearchFileHeaderForToken(pIOHandler, pFile, tokens, 1));
        return found;
    }
    return false;
}

// ------------------------------------------------------------------------------------------------
// List all extensions handled by this loader
const aiImporterDesc *IFCImporter::GetInfo() const {
    return &desc;
}

// ------------------------------------------------------------------------------------------------
// Setup configuration properties for the loader
void IFCImporter::SetupProperties(const Importer *pImp) {
    settings.skipSpaceRepresentations = pImp->GetPropertyBool(AI_CONFIG_IMPORT_IFC_SKIP_SPACE_REPRESENTATIONS, true);
    settings.useCustomTriangulation = pImp->GetPropertyBool(AI_CONFIG_IMPORT_IFC_CUSTOM_TRIANGULATION, true);
    settings.conicSamplingAngle = std::min(std::max((float)pImp->GetPropertyFloat(AI_CONFIG_IMPORT_IFC_SMOOTHING_ANGLE, AI_IMPORT_IFC_DEFAULT_SMOOTHING_ANGLE), 5.0f), 120.0f);
    settings.cylindricalTessellation = std::min(std::max(pImp->GetPropertyInteger(AI_CONFIG_IMPORT_IFC_CYLINDRICAL_TESSELLATION, AI_IMPORT_IFC_DEFAULT_CYLINDRICAL_TESSELLATION), 3), 180);
    settings.skipAnnotations = true;
}

// ------------------------------------------------------------------------------------------------
// Imports the given file into the given scene structure.
void IFCImporter::InternReadFile(const std::string &pFile, aiScene *pScene, IOSystem *pIOHandler) {
    std::shared_ptr<IOStream> stream(pIOHandler->Open(pFile));
    if (!stream) {
        ThrowException("Could not open file for reading");
    }

    // if this is a ifczip file, decompress its contents first
    if (GetExtension(pFile) == "ifczip") {
#ifndef ASSIMP_BUILD_NO_COMPRESSED_IFC
        unzFile zip = unzOpen(pFile.c_str());
        if (zip == nullptr) {
            ThrowException("Could not open ifczip file for reading, unzip failed");
        }

        // chop 'zip' postfix
        std::string fileName = pFile.substr(0, pFile.length() - 3);

        std::string::size_type s = pFile.find_last_of('\\');
        if (s == std::string::npos) {
            s = pFile.find_last_of('/');
        }
        if (s != std::string::npos) {
            fileName = fileName.substr(s + 1);
        }

        // search file (same name as the IFCZIP except for the file extension) and place file pointer there
        if (UNZ_OK == unzGoToFirstFile(zip)) {
            do {
                // get file size, etc.
                unz_file_info fileInfo;
                char filename[256];
                unzGetCurrentFileInfo(zip, &fileInfo, filename, sizeof(filename), 0, 0, 0, 0);
                if (GetExtension(filename) != "ifc") {
                    continue;
                }
                uint8_t *buff = new uint8_t[fileInfo.uncompressed_size];
                LogInfo("Decompressing IFCZIP file");
                unzOpenCurrentFile(zip);
                size_t total = 0;
                int read = 0;
                do {
                    int bufferSize = fileInfo.uncompressed_size < INT16_MAX ? fileInfo.uncompressed_size : INT16_MAX;
                    void *buffer = malloc(bufferSize);
                    read = unzReadCurrentFile(zip, buffer, bufferSize);
                    if (read > 0) {
                        memcpy((char *)buff + total, buffer, read);
                        total += read;
                    }
                    free(buffer);
                } while (read > 0);
                size_t filesize = fileInfo.uncompressed_size;
                if (total == 0 || size_t(total) != filesize) {
                    delete[] buff;
                    ThrowException("Failed to decompress IFC ZIP file");
                }
                unzCloseCurrentFile(zip);
                stream.reset(new MemoryIOStream(buff, fileInfo.uncompressed_size, true));
                if (unzGoToNextFile(zip) == UNZ_END_OF_LIST_OF_FILE) {
                    ThrowException("Found no IFC file member in IFCZIP file (1)");
                }
                break;

            } while (true);
        } else {
            ThrowException("Found no IFC file member in IFCZIP file (2)");
        }

        unzClose(zip);
#else
        ThrowException("Could not open ifczip file for reading, assimp was built without ifczip support");
#endif
    }

    std::unique_ptr<STEP::DB> db(STEP::ReadFileHeader(stream));
    const STEP::HeaderInfo &head = static_cast<const STEP::DB &>(*db).GetHeader();

    if (!head.fileSchema.size() || head.fileSchema.substr(0, 3) != "IFC") {
        ThrowException("Unrecognized file schema: " + head.fileSchema);
    }

    if (!DefaultLogger::isNullLogger()) {
        LogDebug("File schema is \'", head.fileSchema, '\'');
        if (head.timestamp.length()) {
            LogDebug("Timestamp \'", head.timestamp, '\'');
        }
        if (head.app.length()) {
            LogDebug("Application/Exporter identline is \'", head.app, '\'');
        }
    }

    // obtain a copy of the machine-generated IFC scheme
    ::Assimp::STEP::EXPRESS::ConversionSchema schema;
    Schema_2x3::GetSchema(schema);

    // tell the reader which entity types to track with special care
    static const char *const types_to_track[] = {
        "ifcsite", "ifcbuilding", "ifcproject"
    };

    // tell the reader for which types we need to simulate STEPs reverse indices
    static const char *const inverse_indices_to_track[] = {
        "ifcrelcontainedinspatialstructure", "ifcrelaggregates", "ifcrelvoidselement", "ifcreldefinesbyproperties", "ifcpropertyset", "ifcstyleditem"
    };

    // feed the IFC schema into the reader and pre-parse all lines
    STEP::ReadFile(*db, schema, types_to_track, inverse_indices_to_track);
    const STEP::LazyObject *proj = db->GetObject("ifcproject");
    if (!proj) {
        ThrowException("missing IfcProject entity");
    }

    ConversionData conv(*db, proj->To<Schema_2x3::IfcProject>(), pScene, settings);
    SetUnits(conv);
    SetCoordinateSpace(conv);
    ProcessSpatialStructures(conv);
    MakeTreeRelative(conv);

// NOTE - this is a stress test for the importer, but it works only
// in a build with no entities disabled. See
//     scripts/IFCImporter/CPPGenerator.py
// for more information.
#ifdef ASSIMP_IFC_TEST
    db->EvaluateAll();
#endif

    // do final data copying
    if (conv.meshes.size()) {
        pScene->mNumMeshes = static_cast<unsigned int>(conv.meshes.size());
        pScene->mMeshes = new aiMesh *[pScene->mNumMeshes]();
        std::copy(conv.meshes.begin(), conv.meshes.end(), pScene->mMeshes);

        // needed to keep the d'tor from burning us
        conv.meshes.clear();
    }

    if (conv.materials.size()) {
        pScene->mNumMaterials = static_cast<unsigned int>(conv.materials.size());
        pScene->mMaterials = new aiMaterial *[pScene->mNumMaterials]();
        std::copy(conv.materials.begin(), conv.materials.end(), pScene->mMaterials);

        // needed to keep the d'tor from burning us
        conv.materials.clear();
    }

    // apply world coordinate system (which includes the scaling to convert to meters and a -90 degrees rotation around x)
    aiMatrix4x4 scale, rot;
    aiMatrix4x4::Scaling(static_cast<aiVector3D>(IfcVector3(conv.len_scale)), scale);
    aiMatrix4x4::RotationX(-AI_MATH_HALF_PI_F, rot);

    pScene->mRootNode->mTransformation = rot * scale * conv.wcs * pScene->mRootNode->mTransformation;

    // this must be last because objects are evaluated lazily as we process them
    if (!DefaultLogger::isNullLogger()) {
        LogDebug("STEP: evaluated ", db->GetEvaluatedObjectCount(), " object records");
    }
}

namespace {

// ------------------------------------------------------------------------------------------------
void ConvertUnit(const Schema_2x3::IfcNamedUnit &unit, ConversionData &conv) {
    if (const Schema_2x3::IfcSIUnit *const si = unit.ToPtr<Schema_2x3::IfcSIUnit>()) {
        if (si->UnitType == "LENGTHUNIT") {
            conv.len_scale = si->Prefix ? ConvertSIPrefix(si->Prefix) : 1.f;
            IFCImporter::LogDebug("got units used for lengths");
        }
        if (si->UnitType == "PLANEANGLEUNIT") {
            if (si->Name != "RADIAN") {
                IFCImporter::LogWarn("expected base unit for angles to be radian");
            }
        }
    } else if (const Schema_2x3::IfcConversionBasedUnit *const convu = unit.ToPtr<Schema_2x3::IfcConversionBasedUnit>()) {
        if (convu->UnitType == "PLANEANGLEUNIT") {
            try {
                conv.angle_scale = convu->ConversionFactor->ValueComponent->To<::Assimp::STEP::EXPRESS::REAL>();
                ConvertUnit(*convu->ConversionFactor->UnitComponent, conv);
                IFCImporter::LogDebug("got units used for angles");
            } catch (std::bad_cast &) {
                IFCImporter::LogError("skipping unknown IfcConversionBasedUnit.ValueComponent entry - expected REAL");
            }
        }
    }
}

// ------------------------------------------------------------------------------------------------
void ConvertUnit(const ::Assimp::STEP::EXPRESS::DataType &dt, ConversionData &conv) {
    try {
        const ::Assimp::STEP::EXPRESS::ENTITY &e = dt.To<::Assimp::STEP::EXPRESS::ENTITY>();

        const Schema_2x3::IfcNamedUnit &unit = e.ResolveSelect<Schema_2x3::IfcNamedUnit>(conv.db);
        if (unit.UnitType != "LENGTHUNIT" && unit.UnitType != "PLANEANGLEUNIT") {
            return;
        }

        ConvertUnit(unit, conv);
    } catch (std::bad_cast &) {
        // not entity, somehow
        IFCImporter::LogError("skipping unknown IfcUnit entry - expected entity");
    }
}

// ------------------------------------------------------------------------------------------------
void SetUnits(ConversionData &conv) {
    // see if we can determine the coordinate space used to express.
    for (size_t i = 0; i < conv.proj.UnitsInContext->Units.size(); ++i) {
        ConvertUnit(*conv.proj.UnitsInContext->Units[i], conv);
    }
}

// ------------------------------------------------------------------------------------------------
void SetCoordinateSpace(ConversionData &conv) {
    const Schema_2x3::IfcRepresentationContext *fav = nullptr;
    for (const Schema_2x3::IfcRepresentationContext &v : conv.proj.RepresentationContexts) {
        fav = &v;
        // Model should be the most suitable type of context, hence ignore the others
        if (v.ContextType && v.ContextType.Get() == "Model") {
            break;
        }
    }
    if (fav) {
        if (const Schema_2x3::IfcGeometricRepresentationContext *const geo = fav->ToPtr<Schema_2x3::IfcGeometricRepresentationContext>()) {
            ConvertAxisPlacement(conv.wcs, *geo->WorldCoordinateSystem, conv);
            IFCImporter::LogDebug("got world coordinate system");
        }
    }
}

// ------------------------------------------------------------------------------------------------
void ResolveObjectPlacement(aiMatrix4x4 &m, const Schema_2x3::IfcObjectPlacement &place, ConversionData &conv) {
    if (const Schema_2x3::IfcLocalPlacement *const local = place.ToPtr<Schema_2x3::IfcLocalPlacement>()) {
        IfcMatrix4 tmp;
        ConvertAxisPlacement(tmp, *local->RelativePlacement, conv);

        m = static_cast<aiMatrix4x4>(tmp);

        if (local->PlacementRelTo) {
            aiMatrix4x4 tmpM;
            ResolveObjectPlacement(tmpM, local->PlacementRelTo.Get(), conv);
            m = tmpM * m;
        }
    } else {
        IFCImporter::LogWarn("skipping unknown IfcObjectPlacement entity, type is ", place.GetClassName());
    }
}

// ------------------------------------------------------------------------------------------------
bool ProcessMappedItem(const Schema_2x3::IfcMappedItem &mapped, aiNode *nd_src, std::vector<aiNode *> &subnodes_src, unsigned int matid, ConversionData &conv) {
    // insert a custom node here, the carthesian transform operator is simply a conventional transformation matrix
    std::unique_ptr<aiNode> nd(new aiNode());
    nd->mName.Set("IfcMappedItem");

    // handle the Cartesian operator
    IfcMatrix4 m;
    ConvertTransformOperator(m, *mapped.MappingTarget);

    IfcMatrix4 msrc;
    ConvertAxisPlacement(msrc, *mapped.MappingSource->MappingOrigin, conv);

    msrc = m * msrc;

    std::set<unsigned int> meshes;
    const size_t old_openings = conv.collect_openings ? conv.collect_openings->size() : 0;
    if (conv.apply_openings) {
        IfcMatrix4 minv = msrc;
        minv.Inverse();
        for (TempOpening &open : *conv.apply_openings) {
            open.Transform(minv);
        }
    }

    unsigned int localmatid = ProcessMaterials(mapped.GetID(), matid, conv, false);
    const Schema_2x3::IfcRepresentation &repr = mapped.MappingSource->MappedRepresentation;

    bool got = false;
    for (const Schema_2x3::IfcRepresentationItem &item : repr.Items) {
        if (!ProcessRepresentationItem(item, localmatid, meshes, conv)) {
            IFCImporter::LogWarn("skipping mapped entity of type ", item.GetClassName(), ", no representations could be generated");
        } else
            got = true;
    }

    if (!got) {
        return false;
    }

    AssignAddedMeshes(meshes, nd.get(), conv);
    if (conv.collect_openings) {

        // if this pass serves us only to collect opening geometry,
        // make sure we transform the TempMesh's which we need to
        // preserve as well.
        if (const size_t diff = conv.collect_openings->size() - old_openings) {
            for (size_t i = 0; i < diff; ++i) {
                (*conv.collect_openings)[old_openings + i].Transform(msrc);
            }
        }
    }

    nd->mTransformation = nd_src->mTransformation * static_cast<aiMatrix4x4>(msrc);
    subnodes_src.push_back(nd.release());

    return true;
}

// ------------------------------------------------------------------------------------------------
struct RateRepresentationPredicate {
    int Rate(const Schema_2x3::IfcRepresentation *r) const {
        // the smaller, the better

        if (!r->RepresentationIdentifier) {
            // neutral choice if no extra information is specified
            return 0;
        }

        const std::string &name = r->RepresentationIdentifier.Get();
        if (name == "MappedRepresentation") {
            if (!r->Items.empty()) {
                // take the first item and base our choice on it
                const Schema_2x3::IfcMappedItem *const m = r->Items.front()->ToPtr<Schema_2x3::IfcMappedItem>();
                if (m) {
                    return Rate(m->MappingSource->MappedRepresentation);
                }
            }
            return 100;
        }

        return Rate(name);
    }

    int Rate(const std::string &r) const {
        if (r == "SolidModel") {
            return -3;
        }

        // give strong preference to extruded geometry.
        if (r == "SweptSolid") {
            return -10;
        }

        if (r == "Clipping") {
            return -5;
        }

        // 'Brep' is difficult to get right due to possible voids in the
        // polygon boundaries, so take it only if we are forced to (i.e.
        // if the only alternative is (non-clipping) boolean operations,
        // which are not supported at all).
        if (r == "Brep") {
            return -2;
        }

        // Curves, bounding boxes - those will most likely not be loaded
        // as we can't make any use out of this data. So consider them
        // last.
        if (r == "BoundingBox" || r == "Curve2D") {
            return 100;
        }
        return 0;
    }

    bool operator()(const Schema_2x3::IfcRepresentation *a, const Schema_2x3::IfcRepresentation *b) const {
        return Rate(a) < Rate(b);
    }
};

// ------------------------------------------------------------------------------------------------
void ProcessProductRepresentation(const Schema_2x3::IfcProduct &el, aiNode *nd, std::vector<aiNode *> &subnodes, ConversionData &conv) {
    if (!el.Representation) {
        return;
    }

    // extract Color from metadata, if present
    unsigned int matid = ProcessMaterials(el.GetID(), std::numeric_limits<uint32_t>::max(), conv, false);
    std::set<unsigned int> meshes;

    // we want only one representation type, so bring them in a suitable order (i.e try those
    // that look as if we could read them quickly at first). This way of reading
    // representation is relatively generic and allows the concrete implementations
    // for the different representation types to make some sensible choices what
    // to load and what not to load.
    const STEP::ListOf<STEP::Lazy<Schema_2x3::IfcRepresentation>, 1, 0> &src = el.Representation.Get()->Representations;
    std::vector<const Schema_2x3::IfcRepresentation *> repr_ordered(src.size());
    std::copy(src.begin(), src.end(), repr_ordered.begin());
    std::sort(repr_ordered.begin(), repr_ordered.end(), RateRepresentationPredicate());
    for (const Schema_2x3::IfcRepresentation *repr : repr_ordered) {
        bool res = false;
        for (const Schema_2x3::IfcRepresentationItem &item : repr->Items) {
            if (const Schema_2x3::IfcMappedItem *const geo = item.ToPtr<Schema_2x3::IfcMappedItem>()) {
                res = ProcessMappedItem(*geo, nd, subnodes, matid, conv) || res;
            } else {
                res = ProcessRepresentationItem(item, matid, meshes, conv) || res;
            }
        }
        // if we got something meaningful at this point, skip any further representations
        if (res) {
            break;
        }
    }
    AssignAddedMeshes(meshes, nd, conv);
}

typedef std::map<std::string, std::string> Metadata;

// ------------------------------------------------------------------------------------------------
void ProcessMetadata(const Schema_2x3::ListOf<Schema_2x3::Lazy<Schema_2x3::IfcProperty>, 1, 0> &set, ConversionData &conv, Metadata &properties,
        const std::string &prefix = std::string(),
        unsigned int nest = 0) {
    for (const Schema_2x3::IfcProperty &property : set) {
        const std::string &key = prefix.length() > 0 ? (prefix + "." + property.Name) : property.Name;
        if (const Schema_2x3::IfcPropertySingleValue *const singleValue = property.ToPtr<Schema_2x3::IfcPropertySingleValue>()) {
            if (singleValue->NominalValue) {
                if (const ::Assimp::STEP::EXPRESS::STRING *str = singleValue->NominalValue.Get()->ToPtr<::Assimp::STEP::EXPRESS::STRING>()) {
                    std::string value = static_cast<std::string>(*str);
                    properties[key] = value;
                } else if (const ::Assimp::STEP::EXPRESS::REAL *val1 = singleValue->NominalValue.Get()->ToPtr<::Assimp::STEP::EXPRESS::REAL>()) {
                    float value = static_cast<float>(*val1);
                    std::stringstream s;
                    s << value;
                    properties[key] = s.str();
                } else if (const ::Assimp::STEP::EXPRESS::INTEGER *val2 = singleValue->NominalValue.Get()->ToPtr<::Assimp::STEP::EXPRESS::INTEGER>()) {
                    int64_t curValue = static_cast<int64_t>(*val2);
                    std::stringstream s;
                    s << curValue;
                    properties[key] = s.str();
                }
            }
        } else if (const Schema_2x3::IfcPropertyListValue *const listValue = property.ToPtr<Schema_2x3::IfcPropertyListValue>()) {
            std::stringstream ss;
            ss << "[";
            unsigned index = 0;
            for (const Schema_2x3::IfcValue::Out &v : listValue->ListValues) {
                if (!v) continue;
                if (const ::Assimp::STEP::EXPRESS::STRING *str = v->ToPtr<::Assimp::STEP::EXPRESS::STRING>()) {
                    std::string value = static_cast<std::string>(*str);
                    ss << "'" << value << "'";
                } else if (const ::Assimp::STEP::EXPRESS::REAL *val1 = v->ToPtr<::Assimp::STEP::EXPRESS::REAL>()) {
                    float value = static_cast<float>(*val1);
                    ss << value;
                } else if (const ::Assimp::STEP::EXPRESS::INTEGER *val2 = v->ToPtr<::Assimp::STEP::EXPRESS::INTEGER>()) {
                    int64_t value = static_cast<int64_t>(*val2);
                    ss << value;
                }
                if (index + 1 < listValue->ListValues.size()) {
                    ss << ",";
                }
                index++;
            }
            ss << "]";
            properties[key] = ss.str();
        } else if (const Schema_2x3::IfcComplexProperty *const complexProp = property.ToPtr<Schema_2x3::IfcComplexProperty>()) {
            if (nest > 2) { // mostly arbitrary limit to prevent stack overflow vulnerabilities
                IFCImporter::LogError("maximum nesting level for IfcComplexProperty reached, skipping this property.");
            } else {
                ProcessMetadata(complexProp->HasProperties, conv, properties, key, nest + 1);
            }
        } else {
            properties[key] = std::string();
        }
    }
}

// ------------------------------------------------------------------------------------------------
void ProcessMetadata(uint64_t relDefinesByPropertiesID, ConversionData &conv, Metadata &properties) {
    if (const Schema_2x3::IfcRelDefinesByProperties *const pset = conv.db.GetObject(relDefinesByPropertiesID)->ToPtr<Schema_2x3::IfcRelDefinesByProperties>()) {
        if (const Schema_2x3::IfcPropertySet *const set = conv.db.GetObject(pset->RelatingPropertyDefinition->GetID())->ToPtr<Schema_2x3::IfcPropertySet>()) {
            ProcessMetadata(set->HasProperties, conv, properties);
        }
    }
}

// ------------------------------------------------------------------------------------------------
aiNode *ProcessSpatialStructure(aiNode *parent, const Schema_2x3::IfcProduct &el, ConversionData &conv,
        std::vector<TempOpening> *collect_openings = nullptr) {
    const STEP::DB::RefMap &refs = conv.db.GetRefs();

    // skip over space and annotation nodes - usually, these have no meaning in Assimp's context
    bool skipGeometry = false;
    if (conv.settings.skipSpaceRepresentations) {
        if (el.ToPtr<Schema_2x3::IfcSpace>()) {
            IFCImporter::LogVerboseDebug("skipping IfcSpace entity due to importer settings");
            skipGeometry = true;
        }
    }

    if (conv.settings.skipAnnotations) {
        if (el.ToPtr<Schema_2x3::IfcAnnotation>()) {
            IFCImporter::LogVerboseDebug("skipping IfcAnnotation entity due to importer settings");
            return nullptr;
        }
    }

    // add an output node for this spatial structure
    aiNode *nd(new aiNode);
    nd->mName.Set(el.GetClassName() + "_" + (el.Name ? el.Name.Get() : "Unnamed") + "_" + el.GlobalId);
    nd->mParent = parent;

    conv.already_processed.insert(el.GetID());

    // check for node metadata
    STEP::DB::RefMapRange children = refs.equal_range(el.GetID());
    if (children.first != refs.end()) {
        Metadata properties;
        if (children.first == children.second) {
            // handles single property set
            ProcessMetadata((*children.first).second, conv, properties);
        } else {
            // handles multiple property sets (currently all property sets are merged,
            // which may not be the best solution in the long run)
            for (STEP::DB::RefMap::const_iterator it = children.first; it != children.second; ++it) {
                ProcessMetadata((*it).second, conv, properties);
            }
        }

        if (!properties.empty()) {
            aiMetadata *data = aiMetadata::Alloc(static_cast<unsigned int>(properties.size()));
            unsigned int index(0);
            for (const Metadata::value_type &kv : properties) {
                data->Set(index++, kv.first, aiString(kv.second));
            }
            nd->mMetaData = data;
        }
    }

    if (el.ObjectPlacement) {
        ResolveObjectPlacement(nd->mTransformation, el.ObjectPlacement.Get(), conv);
    }

    std::vector<TempOpening> openings;

    IfcMatrix4 myInv;
    bool didinv = false;

    // convert everything contained directly within this structure,
    // this may result in more nodes.
    std::vector<aiNode *> subnodes;
    try {
        // locate aggregates and 'contained-in-here'-elements of this spatial structure and add them in recursively
        // on our way, collect openings in *this* element
        STEP::DB::RefMapRange range = refs.equal_range(el.GetID());

        for (STEP::DB::RefMapRange range2 = range; range2.first != range.second; ++range2.first) {
            // skip over meshes that have already been processed before. This is strictly necessary
            // because the reverse indices also include references contained in argument lists and
            // therefore every element has a back-reference hold by its parent.
            if (conv.already_processed.find((*range2.first).second) != conv.already_processed.end()) {
                continue;
            }
            const STEP::LazyObject &obj = conv.db.MustGetObject((*range2.first).second);

            // handle regularly-contained elements
            if (const Schema_2x3::IfcRelContainedInSpatialStructure *const cont = obj->ToPtr<Schema_2x3::IfcRelContainedInSpatialStructure>()) {
                if (cont->RelatingStructure->GetID() != el.GetID()) {
                    continue;
                }
                for (const Schema_2x3::IfcProduct &pro : cont->RelatedElements) {
                    if (pro.ToPtr<Schema_2x3::IfcOpeningElement>()) {
                        // IfcOpeningElement is handled below. Sadly we can't use it here as is:
                        // The docs say that opening elements are USUALLY attached to building storey,
                        // but we want them for the building elements to which they belong.
                        continue;
                    }

                    aiNode *const ndnew = ProcessSpatialStructure(nd, pro, conv, nullptr);
                    if (ndnew) {
                        subnodes.push_back(ndnew);
                    }
                }
            }
            // handle openings, which we collect in a list rather than adding them to the node graph
            else if (const Schema_2x3::IfcRelVoidsElement *const fills = obj->ToPtr<Schema_2x3::IfcRelVoidsElement>()) {
                if (fills->RelatingBuildingElement->GetID() == el.GetID()) {
                    const Schema_2x3::IfcFeatureElementSubtraction &open = fills->RelatedOpeningElement;

                    // move opening elements to a separate node since they are semantically different than elements that are just 'contained'
                    std::unique_ptr<aiNode> nd_aggr(new aiNode());
                    nd_aggr->mName.Set("$RelVoidsElement");
                    nd_aggr->mParent = nd;

                    nd_aggr->mTransformation = nd->mTransformation;

                    std::vector<TempOpening> openings_local;
                    aiNode *const ndnew = ProcessSpatialStructure(nd_aggr.get(), open, conv, &openings_local);
                    if (ndnew) {

                        nd_aggr->mNumChildren = 1;
                        nd_aggr->mChildren = new aiNode *[1]();

                        nd_aggr->mChildren[0] = ndnew;

                        if (openings_local.size()) {
                            if (!didinv) {
                                myInv = aiMatrix4x4(nd->mTransformation).Inverse();
                                didinv = true;
                            }

                            // we need all openings to be in the local space of *this* node, so transform them
                            for (TempOpening &op : openings_local) {
                                op.Transform(myInv * nd_aggr->mChildren[0]->mTransformation);
                                openings.push_back(op);
                            }
                        }
                        subnodes.push_back(nd_aggr.release());
                    }
                }
            }
        }

        for (; range.first != range.second; ++range.first) {
            // see note in loop above
            if (conv.already_processed.find((*range.first).second) != conv.already_processed.end()) {
                continue;
            }
            if (const Schema_2x3::IfcRelAggregates *const aggr = conv.db.GetObject((*range.first).second)->ToPtr<Schema_2x3::IfcRelAggregates>()) {
                if (aggr->RelatingObject->GetID() != el.GetID()) {
                    continue;
                }

                // move aggregate elements to a separate node since they are semantically different than elements that are just 'contained'
                std::unique_ptr<aiNode> nd_aggr(new aiNode());
                nd_aggr->mName.Set("$RelAggregates");
                nd_aggr->mParent = nd;

                nd_aggr->mTransformation = nd->mTransformation;

                nd_aggr->mChildren = new aiNode *[aggr->RelatedObjects.size()]();
                for (const Schema_2x3::IfcObjectDefinition &def : aggr->RelatedObjects) {
                    if (const Schema_2x3::IfcProduct *const prod = def.ToPtr<Schema_2x3::IfcProduct>()) {

                        aiNode *const ndnew = ProcessSpatialStructure(nd_aggr.get(), *prod, conv, nullptr);
                        if (ndnew) {
                            nd_aggr->mChildren[nd_aggr->mNumChildren++] = ndnew;
                        }
                    }
                }

                subnodes.push_back(nd_aggr.release());
            }
        }

        conv.collect_openings = collect_openings;
        if (!conv.collect_openings) {
            conv.apply_openings = &openings;
        }

        if (!skipGeometry) {
            ProcessProductRepresentation(el, nd, subnodes, conv);
            conv.apply_openings = conv.collect_openings = nullptr;
        }

        if (subnodes.size()) {
            nd->mChildren = new aiNode *[subnodes.size()]();
            for (aiNode *nd2 : subnodes) {
                nd->mChildren[nd->mNumChildren++] = nd2;
                nd2->mParent = nd;
            }
        }
    } catch (...) {
        // it hurts, but I don't want to pull boost::ptr_vector into -noboost only for these few spots here
        std::for_each(subnodes.begin(), subnodes.end(), delete_fun<aiNode>());
        throw;
    }

    ai_assert(conv.already_processed.find(el.GetID()) != conv.already_processed.end());
    conv.already_processed.erase(conv.already_processed.find(el.GetID()));
    return nd;
}

// ------------------------------------------------------------------------------------------------
void ProcessSpatialStructures(ConversionData &conv) {
    // XXX add support for multiple sites (i.e. IfcSpatialStructureElements with composition == COMPLEX)

    // process all products in the file. it is reasonable to assume that a
    // file that is relevant for us contains at least a site or a building.
    const STEP::DB::ObjectMapByType &map = conv.db.GetObjectsByType();

    ai_assert(map.find("ifcsite") != map.end());
    const STEP::DB::ObjectSet *range = &map.find("ifcsite")->second;

    if (range->empty()) {
        ai_assert(map.find("ifcbuilding") != map.end());
        range = &map.find("ifcbuilding")->second;
        if (range->empty()) {
            // no site, no building -  fail;
            IFCImporter::ThrowException("no root element found (expected IfcBuilding or preferably IfcSite)");
        }
    }

    std::vector<aiNode *> nodes;

    for (const STEP::LazyObject *lz : *range) {
        const Schema_2x3::IfcSpatialStructureElement *const prod = lz->ToPtr<Schema_2x3::IfcSpatialStructureElement>();
        if (!prod) {
            continue;
        }
        IFCImporter::LogVerboseDebug("looking at spatial structure `", (prod->Name ? prod->Name.Get() : "unnamed"), "`", (prod->ObjectType ? " which is of type " + prod->ObjectType.Get() : ""));

        // the primary sites are referenced by an IFCRELAGGREGATES element which assigns them to the IFCPRODUCT
        const STEP::DB::RefMap &refs = conv.db.GetRefs();
        STEP::DB::RefMapRange ref_range = refs.equal_range(conv.proj.GetID());
        for (; ref_range.first != ref_range.second; ++ref_range.first) {
            if (const Schema_2x3::IfcRelAggregates *const aggr = conv.db.GetObject((*ref_range.first).second)->ToPtr<Schema_2x3::IfcRelAggregates>()) {

                for (const Schema_2x3::IfcObjectDefinition &def : aggr->RelatedObjects) {
                    // comparing pointer values is not sufficient, we would need to cast them to the same type first
                    // as there is multiple inheritance in the game.
                    if (def.GetID() == prod->GetID()) {
                        IFCImporter::LogVerboseDebug("selecting this spatial structure as root structure");
                        // got it, this is one primary site.
                        nodes.push_back(ProcessSpatialStructure(nullptr, *prod, conv, nullptr));
                    }
                }
            }
        }
    }

    size_t nb_nodes = nodes.size();

    if (nb_nodes == 0) {
        IFCImporter::LogWarn("failed to determine primary site element, taking all the IfcSite");
        for (const STEP::LazyObject *lz : *range) {
            const Schema_2x3::IfcSpatialStructureElement *const prod = lz->ToPtr<Schema_2x3::IfcSpatialStructureElement>();
            if (!prod) {
                continue;
            }

            nodes.push_back(ProcessSpatialStructure(nullptr, *prod, conv, nullptr));
        }

        nb_nodes = nodes.size();
    }

    if (nb_nodes == 1) {
        conv.out->mRootNode = nodes[0];
    } else if (nb_nodes > 1) {
        conv.out->mRootNode = new aiNode("Root");
        conv.out->mRootNode->mParent = nullptr;
        conv.out->mRootNode->mNumChildren = static_cast<unsigned int>(nb_nodes);
        conv.out->mRootNode->mChildren = new aiNode *[conv.out->mRootNode->mNumChildren];

        for (size_t i = 0; i < nb_nodes; ++i) {
            aiNode *node = nodes[i];

            node->mParent = conv.out->mRootNode;

            conv.out->mRootNode->mChildren[i] = node;
        }
    } else {
        IFCImporter::ThrowException("failed to determine primary site element");
    }
}

// ------------------------------------------------------------------------------------------------
void MakeTreeRelative(aiNode *start, const aiMatrix4x4 &combined) {
    // combined is the parent's absolute transformation matrix
    const aiMatrix4x4 old = start->mTransformation;

    if (!combined.IsIdentity()) {
        start->mTransformation = aiMatrix4x4(combined).Inverse() * start->mTransformation;
    }

    // All nodes store absolute transformations right now, so we need to make them relative
    for (unsigned int i = 0; i < start->mNumChildren; ++i) {
        MakeTreeRelative(start->mChildren[i], old);
    }
}

// ------------------------------------------------------------------------------------------------
void MakeTreeRelative(ConversionData &conv) {
    MakeTreeRelative(conv.out->mRootNode, IfcMatrix4());
}

} // namespace

#endif
