/*
---------------------------------------------------------------------------
Open Asset Import Library (assimp)
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  following disclaimer.

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*/

/** @file  SIBImporter.cpp
 *  @brief Implementation of the SIB importer class.
 *
 *  The Nevercenter Silo SIB format is undocumented.
 *  All details here have been reverse engineered from
 *  studying the binary files output by Silo.
 *
 *  Nevertheless, this implementation is reasonably complete.
 */

#ifndef ASSIMP_BUILD_NO_SIB_IMPORTER

// internal headers
#include "SIBImporter.h"
#include <assimp/ByteSwapper.h>
#include <assimp/StreamReader.h>
#include <assimp/TinyFormatter.h>
#include "utf8.h"
#include <assimp/importerdesc.h>
#include <assimp/scene.h>
#include <assimp/DefaultLogger.hpp>
#include <assimp/IOSystem.hpp>
#include <assimp/StringUtils.h>

#include <map>

namespace Assimp {

static constexpr aiImporterDesc desc = {
    "Silo SIB Importer",
    "Richard Mitton (http://www.codersnotes.com/about)",
    "",
    "Does not apply subdivision.",
    aiImporterFlags_SupportBinaryFlavour,
    0, 0,
    0, 0,
    "sib"
};

struct SIBChunk {
    uint32_t Tag;
    uint32_t Size;
};

enum {
    POS,
    NRM,
    UV,
    N
};

using SIBPair = std::pair<uint32_t, uint32_t>;

struct SIBEdge {
    uint32_t faceA, faceB;
    bool creased;
};

struct SIBMesh {
    aiMatrix4x4 axis;
    uint32_t numPts;
    std::vector<aiVector3D> pos, nrm, uv;
    std::vector<uint32_t> idx;
    std::vector<uint32_t> faceStart;
    std::vector<uint32_t> mtls;
    std::vector<SIBEdge> edges;
    std::map<SIBPair, uint32_t> edgeMap;
};

struct SIBObject {
    aiString name;
    aiMatrix4x4 axis;
    size_t meshIdx, meshCount;
};

struct SIB {
    std::vector<aiMaterial *> mtls;
    std::vector<aiMesh *> meshes;
    std::vector<aiLight *> lights;
    std::vector<SIBObject> objs, insts;
};

// ------------------------------------------------------------------------------------------------
static SIBEdge &GetEdge(SIBMesh *mesh, uint32_t posA, uint32_t posB) {
    SIBPair pair = (posA < posB) ? SIBPair(posA, posB) : SIBPair(posB, posA);
    std::map<SIBPair, uint32_t>::iterator it = mesh->edgeMap.find(pair);
    if (it != mesh->edgeMap.end())
        return mesh->edges[it->second];

    SIBEdge edge;
    edge.creased = false;
    edge.faceA = edge.faceB = 0xffffffff;
    mesh->edgeMap[pair] = static_cast<uint32_t>(mesh->edges.size());
    mesh->edges.push_back(edge);
    return mesh->edges.back();
}

// ------------------------------------------------------------------------------------------------
// Helpers for reading chunked data.

#define TAG(A, B, C, D) ((A << 24) | (B << 16) | (C << 8) | D)

static SIBChunk ReadChunk(StreamReaderLE *stream) {
    SIBChunk chunk;
    chunk.Tag = stream->GetU4();
    chunk.Size = stream->GetU4();
    if (chunk.Size > stream->GetRemainingSizeToLimit())
        ASSIMP_LOG_ERROR("SIB: Chunk overflow");
    ByteSwap::Swap4(&chunk.Tag);
    return chunk;
}

static aiColor3D ReadColor(StreamReaderLE *stream) {
    float r = stream->GetF4();
    float g = stream->GetF4();
    float b = stream->GetF4();
    stream->GetU4(); // Colors have an unused(?) 4th component.
    return aiColor3D(r, g, b);
}

static void UnknownChunk(StreamReaderLE * /*stream*/, const SIBChunk &chunk) {
    char temp[4] = {
        static_cast<char>((chunk.Tag >> 24) & 0xff),
        static_cast<char>((chunk.Tag >> 16) & 0xff),
        static_cast<char>((chunk.Tag >> 8) & 0xff),
        static_cast<char>(chunk.Tag & 0xff)
    };

    ASSIMP_LOG_WARN("SIB: Skipping unknown '", ai_str_toprintable(temp, 4), "' chunk.");
}

// Reads a UTF-16LE string and returns it at UTF-8.
static aiString ReadString(StreamReaderLE *stream, uint32_t numWChars) {
    if (nullptr == stream || 0 == numWChars) {
        return aiString();
    }

    // Allocate buffers (max expansion is 1 byte -> 4 bytes for UTF-8)
    std::vector<unsigned char> str;
    str.reserve(numWChars * 4 + 1);
    uint16_t *temp = new uint16_t[numWChars];
    for (uint32_t n = 0; n < numWChars; ++n) {
        temp[n] = stream->GetU2();
    }

    // Convert it and NUL-terminate.
    const uint16_t *start(temp), *end(temp + numWChars);
    utf8::utf16to8(start, end, back_inserter(str));
    str[str.size() - 1] = '\0';

    // Return the final string.
    aiString result = aiString((const char *)&str[0]);
    delete[] temp;

    return result;
}

// ------------------------------------------------------------------------------------------------
// Returns whether the class can handle the format of the given file.
bool SIBImporter::CanRead(const std::string &filename, IOSystem * /*pIOHandler*/, bool /*checkSig*/) const {
    return SimpleExtensionCheck(filename, "sib");
}

// ------------------------------------------------------------------------------------------------
const aiImporterDesc *SIBImporter::GetInfo() const {
    return &desc;
}

// ------------------------------------------------------------------------------------------------
static void ReadVerts(SIBMesh *mesh, StreamReaderLE *stream, uint32_t count) {
    if (nullptr == mesh || nullptr == stream) {
        return;
    }

    mesh->pos.resize(count);
    for (uint32_t n = 0; n < count; ++n) {
        mesh->pos[n].x = stream->GetF4();
        mesh->pos[n].y = stream->GetF4();
        mesh->pos[n].z = stream->GetF4();
    }
}

// ------------------------------------------------------------------------------------------------
static void ReadFaces(SIBMesh *mesh, StreamReaderLE *stream) {
    uint32_t ptIdx = 0;
    while (stream->GetRemainingSizeToLimit() > 0) {
        uint32_t numPoints = stream->GetU4();

        // Store room for the N index channels, plus the point count.
        size_t pos = mesh->idx.size() + 1;
        mesh->idx.resize(pos + numPoints * N);
        mesh->idx[pos - 1] = numPoints;
        uint32_t *idx = &mesh->idx[pos];

        mesh->faceStart.push_back(static_cast<uint32_t>(pos - 1));
        mesh->mtls.push_back(0);

        // Read all the position data.
        // UV/normals will be supplied later.
        // Positions are supplied indexed already, so we preserve that
        // mapping. UVs are supplied uniquely, so we allocate unique indices.
        for (uint32_t n = 0; n < numPoints; n++, idx += N, ptIdx++) {
            uint32_t p = stream->GetU4();
            if (p >= mesh->pos.size())
                throw DeadlyImportError("Vertex index is out of range.");
            idx[POS] = p;
            idx[NRM] = ptIdx;
            idx[UV] = ptIdx;
        }
    }

    // Allocate data channels for normals/UVs.
    mesh->nrm.resize(ptIdx, aiVector3D(0, 0, 0));
    mesh->uv.resize(ptIdx, aiVector3D(0, 0, 0));

    mesh->numPts = ptIdx;
}

// ------------------------------------------------------------------------------------------------
static void ReadUVs(SIBMesh *mesh, StreamReaderLE *stream) {
    while (stream->GetRemainingSizeToLimit() > 0) {
        uint32_t faceIdx = stream->GetU4();
        uint32_t numPoints = stream->GetU4();

        if (faceIdx >= mesh->faceStart.size())
            throw DeadlyImportError("Invalid face index.");

        uint32_t pos = mesh->faceStart[faceIdx];
        uint32_t *idx = &mesh->idx[pos + 1];

        for (uint32_t n = 0; n < numPoints; n++, idx += N) {
            uint32_t id = idx[UV];
            mesh->uv[id].x = stream->GetF4();
            mesh->uv[id].y = stream->GetF4();
        }
    }
}

// ------------------------------------------------------------------------------------------------
static void ReadMtls(SIBMesh *mesh, StreamReaderLE *stream) {
    // Material assignments are stored run-length encoded.
    // Also, we add 1 to each material so that we can use mtl #0
    // as the default material.
    uint32_t prevFace = stream->GetU4();
    uint32_t prevMtl = stream->GetU4() + 1;
    while (stream->GetRemainingSizeToLimit() > 0) {
        uint32_t face = stream->GetU4();
        uint32_t mtl = stream->GetU4() + 1;
        while (prevFace < face) {
            if (prevFace >= mesh->mtls.size())
                throw DeadlyImportError("Invalid face index.");
            mesh->mtls[prevFace++] = prevMtl;
        }

        prevFace = face;
        prevMtl = mtl;
    }

    while (prevFace < mesh->mtls.size())
        mesh->mtls[prevFace++] = prevMtl;
}

// ------------------------------------------------------------------------------------------------
static void ReadAxis(aiMatrix4x4 &axis, StreamReaderLE *stream) {
    axis.a4 = stream->GetF4();
    axis.b4 = stream->GetF4();
    axis.c4 = stream->GetF4();
    axis.d4 = 1;
    axis.a1 = stream->GetF4();
    axis.b1 = stream->GetF4();
    axis.c1 = stream->GetF4();
    axis.d1 = 0;
    axis.a2 = stream->GetF4();
    axis.b2 = stream->GetF4();
    axis.c2 = stream->GetF4();
    axis.d2 = 0;
    axis.a3 = stream->GetF4();
    axis.b3 = stream->GetF4();
    axis.c3 = stream->GetF4();
    axis.d3 = 0;
}

// ------------------------------------------------------------------------------------------------
static void ReadEdges(SIBMesh *mesh, StreamReaderLE *stream) {
    while (stream->GetRemainingSizeToLimit() > 0) {
        uint32_t posA = stream->GetU4();
        uint32_t posB = stream->GetU4();
        GetEdge(mesh, posA, posB);
    }
}

// ------------------------------------------------------------------------------------------------
static void ReadCreases(SIBMesh *mesh, StreamReaderLE *stream) {
    while (stream->GetRemainingSizeToLimit() > 0) {
        uint32_t edge = stream->GetU4();
        if (edge >= mesh->edges.size())
            throw DeadlyImportError("SIB: Invalid edge index.");
        mesh->edges[edge].creased = true;
    }
}

// ------------------------------------------------------------------------------------------------
static void ConnectFaces(SIBMesh *mesh) {
    // Find faces connected to each edge.
    size_t numFaces = mesh->faceStart.size();
    for (size_t faceIdx = 0; faceIdx < numFaces; faceIdx++) {
        uint32_t *idx = &mesh->idx[mesh->faceStart[faceIdx]];
        uint32_t numPoints = *idx++;
        uint32_t prev = idx[(numPoints - 1) * N + POS];

        for (uint32_t i = 0; i < numPoints; i++, idx += N) {
            uint32_t next = idx[POS];

            // Find this edge.
            SIBEdge &edge = GetEdge(mesh, prev, next);

            // Link this face onto it.
            // This gives potentially undesirable normals when used
            // with non-2-manifold surfaces, but then so does Silo to begin with.
            if (edge.faceA == 0xffffffff)
                edge.faceA = static_cast<uint32_t>(faceIdx);
            else if (edge.faceB == 0xffffffff)
                edge.faceB = static_cast<uint32_t>(faceIdx);

            prev = next;
        }
    }
}

// ------------------------------------------------------------------------------------------------
static aiVector3D CalculateVertexNormal(SIBMesh *mesh, uint32_t faceIdx, uint32_t pos,
        const std::vector<aiVector3D> &faceNormals) {
    // Creased edges complicate this. We need to find the start/end range of the
    // ring of faces that touch this position.
    // We do this in two passes. The first pass is to find the end of the range,
    // the second is to work backwards to the start and calculate the final normal.
    aiVector3D vtxNormal;
    for (int pass = 0; pass < 2; pass++) {
        vtxNormal = aiVector3D(0, 0, 0);
        uint32_t startFaceIdx = faceIdx;
        uint32_t prevFaceIdx = faceIdx;

        // Process each connected face.
        while (true) {
            // Accumulate the face normal.
            vtxNormal += faceNormals[faceIdx];

            uint32_t nextFaceIdx = 0xffffffff;

            // Move to the next edge sharing this position.
            uint32_t *idx = &mesh->idx[mesh->faceStart[faceIdx]];
            uint32_t numPoints = *idx++;
            uint32_t posA = idx[(numPoints - 1) * N + POS];
            for (uint32_t n = 0; n < numPoints; n++, idx += N) {
                uint32_t posB = idx[POS];

                // Test if this edge shares our target position.
                if (posA == pos || posB == pos) {
                    SIBEdge &edge = GetEdge(mesh, posA, posB);

                    // Non-manifold meshes can produce faces which share
                    // positions but have no edge entry, so check it.
                    if (edge.faceA == faceIdx || edge.faceB == faceIdx) {
                        // Move to whichever side we didn't just come from.
                        if (!edge.creased) {
                            if (edge.faceA != prevFaceIdx && edge.faceA != faceIdx && edge.faceA != 0xffffffff)
                                nextFaceIdx = edge.faceA;
                            else if (edge.faceB != prevFaceIdx && edge.faceB != faceIdx && edge.faceB != 0xffffffff)
                                nextFaceIdx = edge.faceB;
                        }
                    }
                }

                posA = posB;
            }

            // Stop once we hit either an creased/unconnected edge, or we
            // wrapped around and hit our start point.
            if (nextFaceIdx == 0xffffffff || nextFaceIdx == startFaceIdx)
                break;

            prevFaceIdx = faceIdx;
            faceIdx = nextFaceIdx;
        }
    }

    // Normalize it.
    float len = vtxNormal.Length();
    if (len > 0.000000001f)
        vtxNormal /= len;
    return vtxNormal;
}

// ------------------------------------------------------------------------------------------------
static void CalculateNormals(SIBMesh *mesh) {
    size_t numFaces = mesh->faceStart.size();

    // Calculate face normals.
    std::vector<aiVector3D> faceNormals(numFaces);
    for (size_t faceIdx = 0; faceIdx < numFaces; faceIdx++) {
        uint32_t *idx = &mesh->idx[mesh->faceStart[faceIdx]];
        uint32_t numPoints = *idx++;

        aiVector3D faceNormal(0, 0, 0);

        uint32_t *prev = &idx[(numPoints - 1) * N];

        for (uint32_t i = 0; i < numPoints; i++) {
            uint32_t *next = &idx[i * N];

            faceNormal += mesh->pos[prev[POS]] ^ mesh->pos[next[POS]];
            prev = next;
        }

        faceNormals[faceIdx] = faceNormal;
    }

    // Calculate vertex normals.
    for (size_t faceIdx = 0; faceIdx < numFaces; faceIdx++) {
        uint32_t *idx = &mesh->idx[mesh->faceStart[faceIdx]];
        uint32_t numPoints = *idx++;

        for (uint32_t i = 0; i < numPoints; i++) {
            uint32_t pos = idx[i * N + POS];
            uint32_t nrm = idx[i * N + NRM];
            aiVector3D vtxNorm = CalculateVertexNormal(mesh, static_cast<uint32_t>(faceIdx), pos, faceNormals);
            mesh->nrm[nrm] = vtxNorm;
        }
    }
}

// ------------------------------------------------------------------------------------------------
struct TempMesh {
    std::vector<aiVector3D> vtx;
    std::vector<aiVector3D> nrm;
    std::vector<aiVector3D> uv;
    std::vector<aiFace> faces;
};

static void ReadShape(SIB *sib, StreamReaderLE *stream) {
    SIBMesh smesh;
    aiString name;

    while (stream->GetRemainingSizeToLimit() >= sizeof(SIBChunk)) {
        SIBChunk chunk = ReadChunk(stream);
        unsigned oldLimit = stream->SetReadLimit(stream->GetCurrentPos() + chunk.Size);

        switch (chunk.Tag) {
        case TAG('M', 'I', 'R', 'P'): break; // mirror plane maybe?
        case TAG('I', 'M', 'R', 'P'): break; // instance mirror? (not supported here yet)
        case TAG('D', 'I', 'N', 'F'): break; // display info, not needed
        case TAG('P', 'I', 'N', 'F'): break; // ?
        case TAG('V', 'M', 'I', 'R'): break; // ?
        case TAG('F', 'M', 'I', 'R'): break; // ?
        case TAG('T', 'X', 'S', 'M'): break; // ?
        case TAG('F', 'A', 'H', 'S'): break; // ?
        case TAG('V', 'R', 'T', 'S'): ReadVerts(&smesh, stream, chunk.Size / 12); break;
        case TAG('F', 'A', 'C', 'S'): ReadFaces(&smesh, stream); break;
        case TAG('F', 'T', 'V', 'S'): ReadUVs(&smesh, stream); break;
        case TAG('S', 'N', 'A', 'M'): name = ReadString(stream, chunk.Size / 2); break;
        case TAG('F', 'A', 'M', 'A'): ReadMtls(&smesh, stream); break;
        case TAG('A', 'X', 'I', 'S'): ReadAxis(smesh.axis, stream); break;
        case TAG('E', 'D', 'G', 'S'): ReadEdges(&smesh, stream); break;
        case TAG('E', 'C', 'R', 'S'): ReadCreases(&smesh, stream); break;
        default: UnknownChunk(stream, chunk); break;
        }

        stream->SetCurrentPos(stream->GetReadLimit());
        stream->SetReadLimit(oldLimit);
    }

    ai_assert(smesh.faceStart.size() == smesh.mtls.size()); // sanity check

    // Silo doesn't store any normals in the file - we need to compute
    // them ourselves. We can't let AssImp handle it as AssImp doesn't
    // know about our creased edges.
    ConnectFaces(&smesh);
    CalculateNormals(&smesh);

    // Construct the transforms.
    aiMatrix4x4 worldToLocal = smesh.axis;
    worldToLocal.Inverse();
    aiMatrix4x4 worldToLocalN = worldToLocal;
    worldToLocalN.a4 = worldToLocalN.b4 = worldToLocalN.c4 = 0.0f;
    worldToLocalN.Inverse().Transpose();

    // Allocate final mesh data.
    // We'll allocate one mesh for each material. (we'll strip unused ones after)
    std::vector<TempMesh> meshes(sib->mtls.size());

    // Un-index the source data and apply to each vertex.
    for (unsigned fi = 0; fi < smesh.faceStart.size(); fi++) {
        uint32_t start = smesh.faceStart[fi];
        uint32_t mtl = smesh.mtls[fi];
        uint32_t *idx = &smesh.idx[start];

        if (mtl >= meshes.size()) {
            ASSIMP_LOG_ERROR("SIB: Face material index is invalid.");
            mtl = 0;
        }

        TempMesh &dest = meshes[mtl];

        aiFace face;
        face.mNumIndices = *idx++;
        face.mIndices = new unsigned[face.mNumIndices];
        for (unsigned pt = 0; pt < face.mNumIndices; pt++, idx += N) {
            size_t vtxIdx = dest.vtx.size();
            face.mIndices[pt] = static_cast<unsigned int>(vtxIdx);

            // De-index it. We don't need to validate here as
            // we did it when creating the data.
            aiVector3D pos = smesh.pos[idx[POS]];
            aiVector3D nrm = smesh.nrm[idx[NRM]];
            aiVector3D uv = smesh.uv[idx[UV]];

            // The verts are supplied in world-space, so let's
            // transform them back into the local space of this mesh:
            pos = worldToLocal * pos;
            nrm = worldToLocalN * nrm;

            dest.vtx.push_back(pos);
            dest.nrm.push_back(nrm);
            dest.uv.push_back(uv);
        }
        dest.faces.push_back(face);
    }

    SIBObject obj;
    obj.name = name;
    obj.axis = smesh.axis;
    obj.meshIdx = sib->meshes.size();

    // Now that we know the size of everything,
    // we can build the final one-material-per-mesh data.
    for (size_t n = 0; n < meshes.size(); n++) {
        TempMesh &src = meshes[n];
        if (src.faces.empty())
            continue;

        aiMesh *mesh = new aiMesh;
        mesh->mName = name;
        mesh->mNumFaces = static_cast<unsigned int>(src.faces.size());
        mesh->mFaces = new aiFace[mesh->mNumFaces];
        mesh->mNumVertices = static_cast<unsigned int>(src.vtx.size());
        mesh->mVertices = new aiVector3D[mesh->mNumVertices];
        mesh->mNormals = new aiVector3D[mesh->mNumVertices];
        mesh->mTextureCoords[0] = new aiVector3D[mesh->mNumVertices];
        mesh->mNumUVComponents[0] = 2;
        mesh->mMaterialIndex = static_cast<unsigned int>(n);

        for (unsigned i = 0; i < mesh->mNumVertices; i++) {
            mesh->mVertices[i] = src.vtx[i];
            mesh->mNormals[i] = src.nrm[i];
            mesh->mTextureCoords[0][i] = src.uv[i];
        }
        for (unsigned i = 0; i < mesh->mNumFaces; i++) {
            mesh->mFaces[i] = src.faces[i];
        }

        sib->meshes.push_back(mesh);
    }

    obj.meshCount = sib->meshes.size() - obj.meshIdx;
    sib->objs.push_back(obj);
}

// ------------------------------------------------------------------------------------------------
static void ReadMaterial(SIB *sib, StreamReaderLE *stream) {
    aiColor3D diff = ReadColor(stream);
    aiColor3D ambi = ReadColor(stream);
    aiColor3D spec = ReadColor(stream);
    aiColor3D emis = ReadColor(stream);
    float shiny = (float)stream->GetU4();

    uint32_t nameLen = stream->GetU4();
    aiString name = ReadString(stream, nameLen / 2);
    uint32_t texLen = stream->GetU4();
    aiString tex = ReadString(stream, texLen / 2);

    aiMaterial *mtl = new aiMaterial();
    mtl->AddProperty(&diff, 1, AI_MATKEY_COLOR_DIFFUSE);
    mtl->AddProperty(&ambi, 1, AI_MATKEY_COLOR_AMBIENT);
    mtl->AddProperty(&spec, 1, AI_MATKEY_COLOR_SPECULAR);
    mtl->AddProperty(&emis, 1, AI_MATKEY_COLOR_EMISSIVE);
    mtl->AddProperty(&shiny, 1, AI_MATKEY_SHININESS);
    mtl->AddProperty(&name, AI_MATKEY_NAME);
    if (tex.length > 0) {
        mtl->AddProperty(&tex, AI_MATKEY_TEXTURE_DIFFUSE(0));
        mtl->AddProperty(&tex, AI_MATKEY_TEXTURE_AMBIENT(0));
    }

    sib->mtls.push_back(mtl);
}

// ------------------------------------------------------------------------------------------------
static void ReadLightInfo(aiLight *light, StreamReaderLE *stream) {
    uint32_t type = stream->GetU4();
    switch (type) {
    case 0: light->mType = aiLightSource_POINT; break;
    case 1: light->mType = aiLightSource_SPOT; break;
    case 2: light->mType = aiLightSource_DIRECTIONAL; break;
    default: light->mType = aiLightSource_UNDEFINED; break;
    }

    light->mPosition.x = stream->GetF4();
    light->mPosition.y = stream->GetF4();
    light->mPosition.z = stream->GetF4();
    light->mDirection.x = stream->GetF4();
    light->mDirection.y = stream->GetF4();
    light->mDirection.z = stream->GetF4();
    light->mColorDiffuse = ReadColor(stream);
    light->mColorAmbient = ReadColor(stream);
    light->mColorSpecular = ReadColor(stream);
    ai_real spotExponent = stream->GetF4();
    ai_real spotCutoff = stream->GetF4();
    light->mAttenuationConstant = stream->GetF4();
    light->mAttenuationLinear = stream->GetF4();
    light->mAttenuationQuadratic = stream->GetF4();

    // Silo uses the OpenGL default lighting model for it's
    // spot cutoff/exponent. AssImp unfortunately, does not.
    // Let's try and approximate it by solving for the
    // 99% and 1% percentiles.
    //    OpenGL: I = cos(angle)^E
    //   Solving: angle = acos(I^(1/E))
    ai_real E = ai_real(1.0) / std::max(spotExponent, (ai_real)0.00001);
    ai_real inner = std::acos(std::pow((ai_real)0.99, E));
    ai_real outer = std::acos(std::pow((ai_real)0.01, E));

    // Apply the cutoff.
    outer = std::min(outer, AI_DEG_TO_RAD(spotCutoff));

    light->mAngleInnerCone = std::min(inner, outer);
    light->mAngleOuterCone = outer;
}

static void ReadLight(SIB *sib, StreamReaderLE *stream) {
    aiLight *light = new aiLight();

    while (stream->GetRemainingSizeToLimit() >= sizeof(SIBChunk)) {
        SIBChunk chunk = ReadChunk(stream);
        unsigned oldLimit = stream->SetReadLimit(stream->GetCurrentPos() + chunk.Size);

        switch (chunk.Tag) {
        case TAG('L', 'N', 'F', 'O'): ReadLightInfo(light, stream); break;
        case TAG('S', 'N', 'A', 'M'): light->mName = ReadString(stream, chunk.Size / 2); break;
        default: UnknownChunk(stream, chunk); break;
        }

        stream->SetCurrentPos(stream->GetReadLimit());
        stream->SetReadLimit(oldLimit);
    }

    sib->lights.push_back(light);
}

// ------------------------------------------------------------------------------------------------
static void ReadScale(aiMatrix4x4 &axis, StreamReaderLE *stream) {
    aiMatrix4x4 scale;
    scale.a1 = stream->GetF4();
    scale.b1 = stream->GetF4();
    scale.c1 = stream->GetF4();
    scale.d1 = stream->GetF4();
    scale.a2 = stream->GetF4();
    scale.b2 = stream->GetF4();
    scale.c2 = stream->GetF4();
    scale.d2 = stream->GetF4();
    scale.a3 = stream->GetF4();
    scale.b3 = stream->GetF4();
    scale.c3 = stream->GetF4();
    scale.d3 = stream->GetF4();
    scale.a4 = stream->GetF4();
    scale.b4 = stream->GetF4();
    scale.c4 = stream->GetF4();
    scale.d4 = stream->GetF4();

    axis = axis * scale;
}

static void ReadInstance(SIB *sib, StreamReaderLE *stream) {
    SIBObject inst;
    uint32_t shapeIndex = 0;

    while (stream->GetRemainingSizeToLimit() >= sizeof(SIBChunk)) {
        SIBChunk chunk = ReadChunk(stream);
        unsigned oldLimit = stream->SetReadLimit(stream->GetCurrentPos() + chunk.Size);

        switch (chunk.Tag) {
        case TAG('D', 'I', 'N', 'F'): break; // display info, not needed
        case TAG('P', 'I', 'N', 'F'): break; // ?
        case TAG('A', 'X', 'I', 'S'): ReadAxis(inst.axis, stream); break;
        case TAG('I', 'N', 'S', 'I'): shapeIndex = stream->GetU4(); break;
        case TAG('S', 'M', 'T', 'X'): ReadScale(inst.axis, stream); break;
        case TAG('S', 'N', 'A', 'M'): inst.name = ReadString(stream, chunk.Size / 2); break;
        default: UnknownChunk(stream, chunk); break;
        }

        stream->SetCurrentPos(stream->GetReadLimit());
        stream->SetReadLimit(oldLimit);
    }

    if (shapeIndex >= sib->objs.size()) {
        throw DeadlyImportError("SIB: Invalid shape index.");
    }

    const SIBObject &src = sib->objs[shapeIndex];
    inst.meshIdx = src.meshIdx;
    inst.meshCount = src.meshCount;
    sib->insts.push_back(inst);
}

// ------------------------------------------------------------------------------------------------
static void CheckVersion(StreamReaderLE *stream) {
    uint32_t version = stream->GetU4();
    if (version < 1 || version > 2) {
        throw DeadlyImportError("SIB: Unsupported file version.");
    }
}

static void ReadScene(SIB *sib, StreamReaderLE *stream) {
    // Parse each chunk in turn.
    while (stream->GetRemainingSizeToLimit() >= sizeof(SIBChunk)) {
        SIBChunk chunk = ReadChunk(stream);
        unsigned oldLimit = stream->SetReadLimit(stream->GetCurrentPos() + chunk.Size);

        switch (chunk.Tag) {
        case TAG('H', 'E', 'A', 'D'): CheckVersion(stream); break;
        case TAG('S', 'H', 'A', 'P'): ReadShape(sib, stream); break;
        case TAG('G', 'R', 'P', 'S'): break; // group assignment, we don't import this
        case TAG('T', 'E', 'X', 'P'): break; // ?
        case TAG('I', 'N', 'S', 'T'): ReadInstance(sib, stream); break;
        case TAG('M', 'A', 'T', 'R'): ReadMaterial(sib, stream); break;
        case TAG('L', 'G', 'H', 'T'): ReadLight(sib, stream); break;
        default: UnknownChunk(stream, chunk); break;
        }

        stream->SetCurrentPos(stream->GetReadLimit());
        stream->SetReadLimit(oldLimit);
    }
}

// ------------------------------------------------------------------------------------------------
// Imports the given file into the given scene structure.
void SIBImporter::InternReadFile(const std::string &pFile,
        aiScene *pScene, IOSystem *pIOHandler) {

    auto file = pIOHandler->Open(pFile, "rb");
    if (!file)
        throw DeadlyImportError("SIB: Could not open ", pFile);

    StreamReaderLE stream(file);

    // We should have at least one chunk
    if (stream.GetRemainingSize() < 16)
        throw DeadlyImportError("SIB file is either empty or corrupt: ", pFile);

    SIB sib;

    // Default material.
    aiMaterial *defmtl = new aiMaterial;
    aiString defname = aiString(AI_DEFAULT_MATERIAL_NAME);
    defmtl->AddProperty(&defname, AI_MATKEY_NAME);
    sib.mtls.push_back(defmtl);

    // Read it all.
    ReadScene(&sib, &stream);

    // Join the instances and objects together.
    size_t firstInst = sib.objs.size();
    sib.objs.insert(sib.objs.end(), sib.insts.begin(), sib.insts.end());
    sib.insts.clear();

    // Transfer to the aiScene.
    pScene->mNumMaterials = static_cast<unsigned int>(sib.mtls.size());
    pScene->mNumMeshes = static_cast<unsigned int>(sib.meshes.size());
    pScene->mNumLights = static_cast<unsigned int>(sib.lights.size());
    pScene->mMaterials = pScene->mNumMaterials ? new aiMaterial *[pScene->mNumMaterials] : nullptr;
    pScene->mMeshes = pScene->mNumMeshes ? new aiMesh *[pScene->mNumMeshes] : nullptr;
    pScene->mLights = pScene->mNumLights ? new aiLight *[pScene->mNumLights] : nullptr;
    if (pScene->mNumMaterials)
        memcpy(pScene->mMaterials, &sib.mtls[0], sizeof(aiMaterial *) * pScene->mNumMaterials);
    if (pScene->mNumMeshes)
        memcpy(pScene->mMeshes, &sib.meshes[0], sizeof(aiMesh *) * pScene->mNumMeshes);
    if (pScene->mNumLights)
        memcpy(pScene->mLights, &sib.lights[0], sizeof(aiLight *) * pScene->mNumLights);

    // Construct the root node.
    size_t childIdx = 0;
    aiNode *root = new aiNode();
    root->mName.Set("<SIBRoot>");
    root->mNumChildren = static_cast<unsigned int>(sib.objs.size() + sib.lights.size());
    root->mChildren = root->mNumChildren ? new aiNode *[root->mNumChildren] : nullptr;
    pScene->mRootNode = root;

    // Add nodes for each object.
    for (size_t n = 0; n < sib.objs.size(); n++) {
        ai_assert(root->mChildren);
        SIBObject &obj = sib.objs[n];
        aiNode *node = new aiNode;
        root->mChildren[childIdx++] = node;
        node->mName = obj.name;
        node->mParent = root;
        node->mTransformation = obj.axis;

        node->mNumMeshes = static_cast<unsigned int>(obj.meshCount);
        node->mMeshes = node->mNumMeshes ? new unsigned[node->mNumMeshes] : nullptr;
        for (unsigned i = 0; i < node->mNumMeshes; i++)
            node->mMeshes[i] = static_cast<unsigned int>(obj.meshIdx + i);

        // Mark instanced objects as being so.
        if (n >= firstInst) {
            node->mMetaData = aiMetadata::Alloc(1);
            node->mMetaData->Set(0, "IsInstance", true);
        }
    }

    // Add nodes for each light.
    // (no transformation as the light is already in world space)
    for (size_t n = 0; n < sib.lights.size(); n++) {
        ai_assert(root->mChildren);
        aiLight *light = sib.lights[n];
        if (nullptr != light) {
            aiNode *node = new aiNode;
            root->mChildren[childIdx++] = node;
            node->mName = light->mName;
            node->mParent = root;
        }
    }
}

} // namespace Assimp

#endif // !! ASSIMP_BUILD_NO_SIB_IMPORTER
