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

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*/

#ifndef ASSIMP_BUILD_NO_EXPORT
#ifndef ASSIMP_BUILD_NO_3DS_EXPORTER

#include "AssetLib/3DS/3DSExporter.h"
#include "AssetLib/3DS/3DSHelper.h"
#include "AssetLib/3DS/3DSLoader.h"
#include "PostProcessing/SplitLargeMeshes.h"

#include <assimp/SceneCombiner.h>
#include <assimp/StringComparison.h>
#include <assimp/DefaultLogger.hpp>
#include <assimp/Exporter.hpp>
#include <assimp/Exceptional.h>
#include <assimp/IOSystem.hpp>

#include <memory>

namespace Assimp {

using namespace D3DS;

namespace {

//////////////////////////////////////////////////////////////////////////////////////
// Scope utility to write a 3DS file chunk.
//
// Upon construction, the chunk header is written with the chunk type (flags)
// filled out, but the chunk size left empty. Upon destruction, the correct chunk
// size based on the then-position of the output stream cursor is filled in.
class ChunkWriter {
    enum {
        CHUNK_SIZE_NOT_SET = 0xdeadbeef,
        SIZE_OFFSET = 2
    };

public:
    ChunkWriter(StreamWriterLE &writer, uint16_t chunk_type) :
            writer(writer) {
        chunk_start_pos = writer.GetCurrentPos();
        writer.PutU2(chunk_type);
        writer.PutU4((uint32_t)CHUNK_SIZE_NOT_SET);
    }

    ~ChunkWriter() {
        std::size_t head_pos = writer.GetCurrentPos();

        ai_assert(head_pos > chunk_start_pos);
        const std::size_t chunk_size = head_pos - chunk_start_pos;

        writer.SetCurrentPos(chunk_start_pos + SIZE_OFFSET);
        writer.PutU4(static_cast<uint32_t>(chunk_size));
        writer.SetCurrentPos(head_pos);
    }

private:
    StreamWriterLE &writer;
    std::size_t chunk_start_pos;
};

// Return an unique name for a given |mesh| attached to |node| that
// preserves the mesh's given name if it has one. |index| is the index
// of the mesh in |aiScene::mMeshes|.
std::string GetMeshName(const aiMesh &mesh, unsigned int index, const aiNode &node) {
    static constexpr char underscore = '_';
    char postfix[10] = { 0 };
    ASSIMP_itoa10(postfix, index);

    std::string result = node.mName.C_Str();
    if (mesh.mName.length > 0) {
        result += underscore;
        result += mesh.mName.C_Str();
    }
    return result + underscore + postfix;
}

// Return an unique name for a given |mat| with original position |index|
// in |aiScene::mMaterials|. The name preserves the original material
// name if possible.
std::string GetMaterialName(const aiMaterial &mat, unsigned int index) {
    static const std::string underscore = "_";
    char postfix[10] = { 0 };
    ASSIMP_itoa10(postfix, index);

    aiString mat_name;
    if (AI_SUCCESS == mat.Get(AI_MATKEY_NAME, mat_name)) {
        return mat_name.C_Str() + underscore + postfix;
    }

    return "Material" + underscore + postfix;
}

// Collect world transformations for each node
void CollectTrafos(const aiNode *node, std::map<const aiNode *, aiMatrix4x4> &trafos) {
    const aiMatrix4x4 &parent = node->mParent ? trafos[node->mParent] : aiMatrix4x4();
    trafos[node] = parent * node->mTransformation;
    for (unsigned int i = 0; i < node->mNumChildren; ++i) {
        CollectTrafos(node->mChildren[i], trafos);
    }
}

// Generate a flat list of the meshes (by index) assigned to each node
void CollectMeshes(const aiNode *node, std::multimap<const aiNode *, unsigned int> &meshes) {
    for (unsigned int i = 0; i < node->mNumMeshes; ++i) {
        meshes.insert(std::make_pair(node, node->mMeshes[i]));
    }
    for (unsigned int i = 0; i < node->mNumChildren; ++i) {
        CollectMeshes(node->mChildren[i], meshes);
    }
}
} // namespace

// ------------------------------------------------------------------------------------------------
// Worker function for exporting a scene to 3DS. Prototyped and registered in Exporter.cpp
void ExportScene3DS(const char *pFile, IOSystem *pIOSystem, const aiScene *pScene, const ExportProperties * /*pProperties*/) {
    std::shared_ptr<IOStream> outfile(pIOSystem->Open(pFile, "wb"));
    if (!outfile) {
        throw DeadlyExportError("Could not open output .3ds file: " + std::string(pFile));
    }

    // TODO: This extra copy should be avoided and all of this made a preprocess
    // requirement of the 3DS exporter.
    //
    // 3DS meshes can be max 0xffff (16 Bit) vertices and faces, respectively.
    // SplitLargeMeshes can do this, but it requires the correct limit to be set
    // which is not possible with the current way of specifying preprocess steps
    // in |Exporter::ExportFormatEntry|.
    aiScene *scenecopy_tmp;
    SceneCombiner::CopyScene(&scenecopy_tmp, pScene);
    std::unique_ptr<aiScene> scenecopy(scenecopy_tmp);

    SplitLargeMeshesProcess_Triangle tri_splitter;
    tri_splitter.SetLimit(0xffff);
    tri_splitter.Execute(scenecopy.get());

    SplitLargeMeshesProcess_Vertex vert_splitter;
    vert_splitter.SetLimit(0xffff);
    vert_splitter.Execute(scenecopy.get());

    // Invoke the actual exporter
    Discreet3DSExporter exporter(outfile, scenecopy.get());
}

} // end of namespace Assimp

// ------------------------------------------------------------------------------------------------
Discreet3DSExporter::Discreet3DSExporter(std::shared_ptr<IOStream> &outfile, const aiScene *scene) :
        scene(scene), writer(outfile) {
    CollectTrafos(scene->mRootNode, trafos);
    CollectMeshes(scene->mRootNode, meshes);

    ChunkWriter curRootChunk(writer, Discreet3DS::CHUNK_MAIN);

    {
        ChunkWriter curChunk(writer, Discreet3DS::CHUNK_OBJMESH);
        WriteMaterials();
        WriteMeshes();

        {
            ChunkWriter curChunk1(writer, Discreet3DS::CHUNK_MASTER_SCALE);
            writer.PutF4(1.0f);
        }
    }

    {
        ChunkWriter curChunk(writer, Discreet3DS::CHUNK_KEYFRAMER);
        WriteHierarchy(*scene->mRootNode, -1, -1);
    }
}

// ------------------------------------------------------------------------------------------------
int Discreet3DSExporter::WriteHierarchy(const aiNode &node, int seq, int sibling_level) {
    // 3DS scene hierarchy is serialized as in http://www.martinreddy.net/gfx/3d/3DS.spec
    {
        ChunkWriter curRootChunk(writer, Discreet3DS::CHUNK_TRACKINFO);
        {
            ChunkWriter curChunk(writer, Discreet3DS::CHUNK_TRACKOBJNAME);

            // Assimp node names are unique and distinct from all mesh-node
            // names we generate; thus we can use them as-is
            WriteString(node.mName);

            // Two unknown int16 values - it is even unclear if 0 is a safe value
            // but luckily importers do not know better either.
            writer.PutI4(0);

            int16_t hierarchy_pos = static_cast<int16_t>(seq);
            if (sibling_level != -1) {
                hierarchy_pos = (uint16_t)sibling_level;
            }

            // Write the hierarchy position
            writer.PutI2(hierarchy_pos);
        }
    }

    // TODO: write transformation chunks

    ++seq;
    sibling_level = seq;

    // Write all children
    for (unsigned int i = 0; i < node.mNumChildren; ++i) {
        seq = WriteHierarchy(*node.mChildren[i], seq, i == 0 ? -1 : sibling_level);
    }

    // Write all meshes as separate nodes to be able to reference the meshes by name
    for (unsigned int i = 0; i < node.mNumMeshes; ++i) {
        const bool first_child = node.mNumChildren == 0 && i == 0;

        const unsigned int mesh_idx = node.mMeshes[i];
        const aiMesh &mesh = *scene->mMeshes[mesh_idx];

        ChunkWriter curChunk(writer, Discreet3DS::CHUNK_TRACKINFO);
        {
            ChunkWriter chunk(writer, Discreet3DS::CHUNK_TRACKOBJNAME);
            WriteString(GetMeshName(mesh, mesh_idx, node));

            writer.PutI4(0);
            writer.PutI2(static_cast<int16_t>(first_child ? seq : sibling_level));
            ++seq;
        }
    }
    return seq;
}

// ------------------------------------------------------------------------------------------------
void Discreet3DSExporter::WriteMaterials() {
    for (unsigned int i = 0; i < scene->mNumMaterials; ++i) {
        ChunkWriter curRootChunk(writer, Discreet3DS::CHUNK_MAT_MATERIAL);
        const aiMaterial &mat = *scene->mMaterials[i];

        {
            ChunkWriter chunk(writer, Discreet3DS::CHUNK_MAT_MATNAME);
            const std::string &name = GetMaterialName(mat, i);
            WriteString(name);
        }

        aiColor3D color;
        if (mat.Get(AI_MATKEY_COLOR_DIFFUSE, color) == AI_SUCCESS) {
            ChunkWriter curChunk(writer, Discreet3DS::CHUNK_MAT_DIFFUSE);
            WriteColor(color);
        }

        if (mat.Get(AI_MATKEY_COLOR_SPECULAR, color) == AI_SUCCESS) {
            ChunkWriter curChunk(writer, Discreet3DS::CHUNK_MAT_SPECULAR);
            WriteColor(color);
        }

        if (mat.Get(AI_MATKEY_COLOR_AMBIENT, color) == AI_SUCCESS) {
            ChunkWriter curChunk(writer, Discreet3DS::CHUNK_MAT_AMBIENT);
            WriteColor(color);
        }

        float f;
        if (mat.Get(AI_MATKEY_OPACITY, f) == AI_SUCCESS) {
            ChunkWriter chunk(writer, Discreet3DS::CHUNK_MAT_TRANSPARENCY);
            WritePercentChunk(1.0f - f);
        }

        if (mat.Get(AI_MATKEY_COLOR_EMISSIVE, color) == AI_SUCCESS) {
            ChunkWriter curChunk(writer, Discreet3DS::CHUNK_MAT_SELF_ILLUM);
            WriteColor(color);
        }

        aiShadingMode shading_mode = aiShadingMode_Flat;
        if (mat.Get(AI_MATKEY_SHADING_MODEL, shading_mode) == AI_SUCCESS) {
            ChunkWriter chunk(writer, Discreet3DS::CHUNK_MAT_SHADING);

            Discreet3DS::shadetype3ds shading_mode_out;
            switch (shading_mode) {
            case aiShadingMode_Flat:
            case aiShadingMode_NoShading:
                shading_mode_out = Discreet3DS::Flat;
                break;

            case aiShadingMode_Gouraud:
            case aiShadingMode_Toon:
            case aiShadingMode_OrenNayar:
            case aiShadingMode_Minnaert:
                shading_mode_out = Discreet3DS::Gouraud;
                break;

            case aiShadingMode_Phong:
            case aiShadingMode_Blinn:
            case aiShadingMode_CookTorrance:
            case aiShadingMode_Fresnel:
            case aiShadingMode_PBR_BRDF: // Possibly should be Discreet3DS::Metal in some cases but this is undocumented
                shading_mode_out = Discreet3DS::Phong;
                break;

            default:
                shading_mode_out = Discreet3DS::Flat;
                ai_assert(false);
            };
            writer.PutU2(static_cast<uint16_t>(shading_mode_out));
        }

        if (mat.Get(AI_MATKEY_SHININESS, f) == AI_SUCCESS) {
            ChunkWriter chunk(writer, Discreet3DS::CHUNK_MAT_SHININESS);
            WritePercentChunk(f);
        }

        if (mat.Get(AI_MATKEY_SHININESS_STRENGTH, f) == AI_SUCCESS) {
            ChunkWriter chunk(writer, Discreet3DS::CHUNK_MAT_SHININESS_PERCENT);
            WritePercentChunk(f);
        }

        int twosided;
        if (mat.Get(AI_MATKEY_TWOSIDED, twosided) == AI_SUCCESS && twosided != 0) {
            ChunkWriter chunk(writer, Discreet3DS::CHUNK_MAT_TWO_SIDE);
            writer.PutI2(1);
        }

        // Fallback to BASE_COLOR if no DIFFUSE
        if (!WriteTexture(mat, aiTextureType_DIFFUSE, Discreet3DS::CHUNK_MAT_TEXTURE))
            WriteTexture(mat, aiTextureType_BASE_COLOR, Discreet3DS::CHUNK_MAT_TEXTURE);

        WriteTexture(mat, aiTextureType_HEIGHT, Discreet3DS::CHUNK_MAT_BUMPMAP);
        WriteTexture(mat, aiTextureType_OPACITY, Discreet3DS::CHUNK_MAT_OPACMAP);
        WriteTexture(mat, aiTextureType_SHININESS, Discreet3DS::CHUNK_MAT_MAT_SHINMAP);
        WriteTexture(mat, aiTextureType_SPECULAR, Discreet3DS::CHUNK_MAT_SPECMAP);
        WriteTexture(mat, aiTextureType_EMISSIVE, Discreet3DS::CHUNK_MAT_SELFIMAP);
        WriteTexture(mat, aiTextureType_REFLECTION, Discreet3DS::CHUNK_MAT_REFLMAP);
    }
}

// ------------------------------------------------------------------------------------------------
// returns true if the texture existed
bool Discreet3DSExporter::WriteTexture(const aiMaterial &mat, aiTextureType type, uint16_t chunk_flags) {
    aiString path;
    aiTextureMapMode map_mode[2] = {
        aiTextureMapMode_Wrap, aiTextureMapMode_Wrap
    };
    ai_real blend = 1.0;
    if (mat.GetTexture(type, 0, &path, nullptr, nullptr, &blend, nullptr, map_mode) != AI_SUCCESS || !path.length) {
        return false;
    }

    // TODO: handle embedded textures properly
    if (path.data[0] == '*') {
        ASSIMP_LOG_ERROR("Ignoring embedded texture for export: ", path.C_Str());
        return false;
    }

    ChunkWriter chunk(writer, chunk_flags);
    {
        ChunkWriter curChunk(writer, Discreet3DS::CHUNK_MAPFILE);
        WriteString(path);
    }

    WritePercentChunk(blend);

    {
        ChunkWriter curChunk(writer, Discreet3DS::CHUNK_MAT_MAP_TILING);
        uint16_t val = 0; // WRAP
        if (map_mode[0] == aiTextureMapMode_Mirror) {
            val = 0x2;
        } else if (map_mode[0] == aiTextureMapMode_Decal) {
            val = 0x10;
        }
        writer.PutU2(val);
    }
    // TODO: export texture transformation (i.e. UV offset, scale, rotation)
    return true;
}

// ------------------------------------------------------------------------------------------------
void Discreet3DSExporter::WriteMeshes() {
    // NOTE: 3DS allows for instances. However:
    //   i)  not all importers support reading them
    //   ii) instances are not as flexible as they are in assimp, in particular,
    //        nodes can carry (and instance) only one mesh.
    //
    // This exporter currently deep clones all instanced meshes, i.e. for each mesh
    // attached to a node a full TRIMESH chunk is written to the file.
    //
    // Furthermore, the TRIMESH is transformed into world space so that it will
    // appear correctly if importers don't read the scene hierarchy at all.
    for (MeshesByNodeMap::const_iterator it = meshes.begin(); it != meshes.end(); ++it) {
        const aiNode &node = *(*it).first;
        const unsigned int mesh_idx = (*it).second;

        const aiMesh &mesh = *scene->mMeshes[mesh_idx];

        // This should not happen if the SLM step is correctly executed
        // before the scene is handed to the exporter
        ai_assert(mesh.mNumVertices <= 0xffff);
        ai_assert(mesh.mNumFaces <= 0xffff);

        const aiMatrix4x4 &trafo = trafos[&node];

        ChunkWriter chunk(writer, Discreet3DS::CHUNK_OBJBLOCK);

        // Mesh name is tied to the node it is attached to so it can later be referenced
        const std::string &name = GetMeshName(mesh, mesh_idx, node);
        WriteString(name);

        // TRIMESH chunk
        ChunkWriter chunk2(writer, Discreet3DS::CHUNK_TRIMESH);

        // Vertices in world space
        {
            ChunkWriter curChunk(writer, Discreet3DS::CHUNK_VERTLIST);

            const uint16_t count = static_cast<uint16_t>(mesh.mNumVertices);
            writer.PutU2(count);
            for (unsigned int i = 0; i < mesh.mNumVertices; ++i) {
                const aiVector3D &v = mesh.mVertices[i];
                writer.PutF4(v.x);
                writer.PutF4(v.y);
                writer.PutF4(v.z);
            }
        }

        // UV coordinates
        if (mesh.HasTextureCoords(0)) {
            ChunkWriter curChunk(writer, Discreet3DS::CHUNK_MAPLIST);
            const uint16_t count = static_cast<uint16_t>(mesh.mNumVertices);
            writer.PutU2(count);

            for (unsigned int i = 0; i < mesh.mNumVertices; ++i) {
                const aiVector3D &v = mesh.mTextureCoords[0][i];
                writer.PutF4(v.x);
                writer.PutF4(v.y);
            }
        }

        // Faces (indices)
        {
            ChunkWriter curChunk(writer, Discreet3DS::CHUNK_FACELIST);

            ai_assert(mesh.mNumFaces <= 0xffff);

            // Count triangles, discard lines and points
            uint16_t count = 0;
            for (unsigned int i = 0; i < mesh.mNumFaces; ++i) {
                const aiFace &f = mesh.mFaces[i];
                if (f.mNumIndices < 3) {
                    continue;
                }
                // TRIANGULATE step is a pre-requisite so we should not see polys here
                ai_assert(f.mNumIndices == 3);
                ++count;
            }

            writer.PutU2(count);
            for (unsigned int i = 0; i < mesh.mNumFaces; ++i) {
                const aiFace &f = mesh.mFaces[i];
                if (f.mNumIndices < 3) {
                    continue;
                }

                for (unsigned int j = 0; j < 3; ++j) {
                    ai_assert(f.mIndices[j] <= 0xffff);
                    writer.PutI2(static_cast<uint16_t>(f.mIndices[j]));
                }

                // Edge visibility flag
                writer.PutI2(0x0);
            }

            // TODO: write smoothing groups (CHUNK_SMOOLIST)

            WriteFaceMaterialChunk(mesh);
        }

        // Transformation matrix by which the mesh vertices have been pre-transformed with.
        {
            ChunkWriter curChunk(writer, Discreet3DS::CHUNK_TRMATRIX);
            // Store rotation 3x3 matrix row wise
            for (unsigned int r = 0; r < 3; ++r) {
                for (unsigned int c = 0; c < 3; ++c) {
                    writer.PutF4(trafo[r][c]);
                }
            }
            // Store translation sub vector column wise
            for (unsigned int r = 0; r < 3; ++r) {
                writer.PutF4(trafo[r][3]);
            }
        }
    }
}

// ------------------------------------------------------------------------------------------------
void Discreet3DSExporter::WriteFaceMaterialChunk(const aiMesh &mesh) {
    ChunkWriter curChunk(writer, Discreet3DS::CHUNK_FACEMAT);
    const std::string &name = GetMaterialName(*scene->mMaterials[mesh.mMaterialIndex], mesh.mMaterialIndex);
    WriteString(name);

    // Because assimp splits meshes by material, only a single
    // FACEMAT chunk needs to be written
    ai_assert(mesh.mNumFaces <= 0xffff);
    const uint16_t count = static_cast<uint16_t>(mesh.mNumFaces);
    writer.PutU2(count);

    for (unsigned int i = 0; i < mesh.mNumFaces; ++i) {
        writer.PutU2(static_cast<uint16_t>(i));
    }
}

// ------------------------------------------------------------------------------------------------
void Discreet3DSExporter::WriteString(const std::string &s) {
    for (std::string::const_iterator it = s.begin(); it != s.end(); ++it) {
        writer.PutI1(*it);
    }
    writer.PutI1('\0');
}

// ------------------------------------------------------------------------------------------------
void Discreet3DSExporter::WriteString(const aiString &s) {
    for (std::size_t i = 0; i < s.length; ++i) {
        writer.PutI1(s.data[i]);
    }
    writer.PutI1('\0');
}

// ------------------------------------------------------------------------------------------------
void Discreet3DSExporter::WriteColor(const aiColor3D &color) {
    ChunkWriter curChunk(writer, Discreet3DS::CHUNK_RGBF);
    writer.PutF4(color.r);
    writer.PutF4(color.g);
    writer.PutF4(color.b);
}

// ------------------------------------------------------------------------------------------------
void Discreet3DSExporter::WritePercentChunk(float f) {
    ChunkWriter curChunk(writer, Discreet3DS::CHUNK_PERCENTF);
    writer.PutF4(f);
}

// ------------------------------------------------------------------------------------------------
void Discreet3DSExporter::WritePercentChunk(double f) {
    ChunkWriter ccurChunkhunk(writer, Discreet3DS::CHUNK_PERCENTD);
    writer.PutF8(f);
}

#endif // ASSIMP_BUILD_NO_3DS_EXPORTER
#endif // ASSIMP_BUILD_NO_EXPORT
