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/** @file  TriangulateProcess.cpp

 *  @brief Implementation of the post processing step to split up

 *    all faces with more than three indices into triangles.

 *

 *

 *  The triangulation algorithm will handle concave or convex polygons.

 *  Self-intersecting or non-planar polygons are not rejected, but

 *  they're probably not triangulated correctly.

 *

 * DEBUG SWITCHES - do not enable any of them in release builds:

 *

 * AI_BUILD_TRIANGULATE_COLOR_FACE_WINDING

 *   - generates vertex colors to represent the face winding order.

 *     the first vertex of a polygon becomes red, the last blue.

 * AI_BUILD_TRIANGULATE_DEBUG_POLYS

 *   - dump all polygons and their triangulation sequences to

 *     a file

 */

#ifndef ASSIMP_BUILD_NO_TRIANGULATE_PROCESS

#include "PostProcessing/TriangulateProcess.h"

#include "PostProcessing/ProcessHelper.h"

#include "Common/PolyTools.h"

#include "contrib/earcut-hpp/earcut.hpp"

#include <memory>

#include <cstdint>

//#define AI_BUILD_TRIANGULATE_COLOR_FACE_WINDING

//#define AI_BUILD_TRIANGULATE_DEBUG_POLYS

#define POLY_GRID_Y 40

#define POLY_GRID_X 70

#define POLY_GRID_XPAD 20

#define POLY_OUTPUT_FILE "assimp_polygons_debug.txt"

namespace mapbox::util {

template <>

struct nth<0, aiVector2D> {

    inline static auto get(const aiVector2D& t) {

        return t.x;

    }

};

template <>

struct nth<1, aiVector2D> {

    inline static auto get(const aiVector2D& t) {

        return t.y;

    }

};

} // namespace mapbox::util

using namespace Assimp;

namespace {

    /**

     * @brief Helper struct used to simplify NGON encoding functions.

     */

    struct NGONEncoder {

        NGONEncoder() : mLastNGONFirstIndex((unsigned int)-1) {}

        /**

         * @brief Encode the current triangle, and make sure it is recognized as a triangle.

         *

         * This method will rotate indices in tri if needed in order to avoid tri to be considered

         * part of the previous ngon. This method is to be used whenever you want to emit a real triangle,

         * and make sure it is seen as a triangle.

         *

         * @param tri Triangle to encode.

         */

        void ngonEncodeTriangle(aiFace * tri) {

            ai_assert(tri->mNumIndices == 3);

            // Rotate indices in new triangle to avoid ngon encoding false ngons

            // Otherwise, the new triangle would be considered part of the previous NGON.

            if (isConsideredSameAsLastNgon(tri)) {

                std::swap(tri->mIndices[0], tri->mIndices[2]);

                std::swap(tri->mIndices[1], tri->mIndices[2]);

            }

            mLastNGONFirstIndex = tri->mIndices[0];

        }

        /**

         * @brief Encode a quad (2 triangles) in ngon encoding, and make sure they are seen as a single ngon.

         *

         * @param tri1 First quad triangle

         * @param tri2 Second quad triangle

         *

         * @pre Triangles must be properly fanned from the most appropriate vertex.

         */

        void ngonEncodeQuad(aiFace *tri1, aiFace *tri2) {

            ai_assert(tri1->mNumIndices == 3);

            ai_assert(tri2->mNumIndices == 3);

            ai_assert(tri1->mIndices[0] == tri2->mIndices[0]);

            // If the selected fanning vertex is the same as the previously

            // emitted ngon, we use the opposite vertex which also happens to work

            // for tri-fanning a concave quad.

            // ref: https://github.com/assimp/assimp/pull/3695#issuecomment-805999760

            if (isConsideredSameAsLastNgon(tri1)) {

                // Right-rotate indices for tri1 (index 2 becomes the new fanning vertex)

                std::swap(tri1->mIndices[0], tri1->mIndices[2]);

                std::swap(tri1->mIndices[1], tri1->mIndices[2]);

                // Left-rotate indices for tri2 (index 2 becomes the new fanning vertex)

                std::swap(tri2->mIndices[1], tri2->mIndices[2]);

                std::swap(tri2->mIndices[0], tri2->mIndices[2]);

                ai_assert(tri1->mIndices[0] == tri2->mIndices[0]);

            }

            mLastNGONFirstIndex = tri1->mIndices[0];

        }

        /**

         * @brief Check whether this triangle would be considered part of the lastly emitted ngon or not.

         *

         * @param tri Current triangle.

         * @return true If used as is, this triangle will be part of last ngon.

         * @return false If used as is, this triangle is not considered part of the last ngon.

         */

        bool isConsideredSameAsLastNgon(const aiFace * tri) const {

            ai_assert(tri->mNumIndices == 3);

            return tri->mIndices[0] == mLastNGONFirstIndex;

        }

    private:

        unsigned int mLastNGONFirstIndex;

    };

}

// ------------------------------------------------------------------------------------------------

// Returns whether the processing step is present in the given flag field.

bool TriangulateProcess::IsActive( unsigned int pFlags) const {

    return (pFlags & aiProcess_Triangulate) != 0;

}

// ------------------------------------------------------------------------------------------------

// Executes the post processing step on the given imported data.

void TriangulateProcess::Execute( aiScene* pScene) {

    ASSIMP_LOG_DEBUG("TriangulateProcess begin");

    bool bHas = false;

    for( unsigned int a = 0; a < pScene->mNumMeshes; a++)

    {

        if (pScene->mMeshes[ a ]) {

            if ( TriangulateMesh( pScene->mMeshes[ a ] ) ) {

                bHas = true;

            }

        }

    }

    if ( bHas ) {

        ASSIMP_LOG_INFO( "TriangulateProcess finished. All polygons have been triangulated." );

    } else {

        ASSIMP_LOG_DEBUG( "TriangulateProcess finished. There was nothing to be done." );

    }

}

// ------------------------------------------------------------------------------------------------

// Triangulates the given mesh.

bool TriangulateProcess::TriangulateMesh( aiMesh* pMesh) {

    // Now we have aiMesh::mPrimitiveTypes, so this is only here for test cases

    if (!pMesh->mPrimitiveTypes)    {

        bool bNeed = false;

        for( unsigned int a = 0; a < pMesh->mNumFaces; a++) {

            const aiFace& face = pMesh->mFaces[a];

            if( face.mNumIndices != 3)  {

                bNeed = true;

            }

        }

        if (!bNeed) {

            return false;

        }

    }

    else if (!(pMesh->mPrimitiveTypes & aiPrimitiveType_POLYGON)) {

        return false;

    }

    // Find out how many output faces we'll get

    uint32_t numOut = 0, max_out = 0;

    bool get_normals = true;

    for( unsigned int a = 0; a < pMesh->mNumFaces; a++) {

        aiFace& face = pMesh->mFaces[a];

        if (face.mNumIndices <= 4) {

            get_normals = false;

        }

        if( face.mNumIndices <= 3) {

            ++numOut;

        } else {

            numOut += face.mNumIndices-2;

            max_out = std::max<uint32_t>(max_out,face.mNumIndices);

        }

    }

    // Just another check whether aiMesh::mPrimitiveTypes is correct

    if (numOut == pMesh->mNumFaces) {

        ASSIMP_LOG_ERROR( "Invalidation detected in the number of indices: does not fit to the primitive type." );

        return false;

    }

    aiVector3D *nor_out = nullptr;

    // if we don't have normals yet, but expect them to be a cheap side

    // product of triangulation anyway, allocate storage for them.

    if (!pMesh->mNormals && get_normals) {

        // XXX need a mechanism to inform the GenVertexNormals process to treat these normals as preprocessed per-face normals

    //  nor_out = pMesh->mNormals = new aiVector3D[pMesh->mNumVertices];

    }

    // the output mesh will contain triangles, but no polys anymore

    pMesh->mPrimitiveTypes |= aiPrimitiveType_TRIANGLE;

    pMesh->mPrimitiveTypes &= ~aiPrimitiveType_POLYGON;

    // The mesh becomes NGON encoded now, during the triangulation process.

    pMesh->mPrimitiveTypes |= aiPrimitiveType_NGONEncodingFlag;

    aiFace* out = new aiFace[numOut](), *curOut = out;

    std::vector<aiVector3D> temp_verts3d(max_out+2); /* temporary storage for vertices */

    std::vector<std::vector<aiVector2D>> temp_poly(1); /* temporary storage for earcut.hpp */

    std::vector<aiVector2D>& temp_verts = temp_poly[0];

    temp_verts.reserve(max_out + 2);

    NGONEncoder ngonEncoder;

    // Apply vertex colors to represent the face winding?

#ifdef AI_BUILD_TRIANGULATE_COLOR_FACE_WINDING

    if (!pMesh->mColors[0])

        pMesh->mColors[0] = new aiColor4D[pMesh->mNumVertices];

    else

        new(pMesh->mColors[0]) aiColor4D[pMesh->mNumVertices];

    aiColor4D* clr = pMesh->mColors[0];

#endif

#ifdef AI_BUILD_TRIANGULATE_DEBUG_POLYS

    FILE* fout = fopen(POLY_OUTPUT_FILE,"a");

#endif

    const aiVector3D* verts = pMesh->mVertices;

    for( unsigned int a = 0; a < pMesh->mNumFaces; a++) {

        aiFace& face = pMesh->mFaces[a];

        unsigned int* idx = face.mIndices;

        unsigned int num = face.mNumIndices;

        // Apply vertex colors to represent the face winding?

#ifdef AI_BUILD_TRIANGULATE_COLOR_FACE_WINDING

        for (unsigned int i = 0; i < face.mNumIndices; ++i) {

            aiColor4D& c = clr[idx[i]];

            c.r = (i+1) / (float)max;

            c.b = 1.f - c.r;

        }

#endif

        aiFace* const last_face = curOut;

        // if it's a simple point,line or triangle: just copy it

        if( face.mNumIndices <= 3)

        {

            aiFace& nface = *curOut++;

            nface.mNumIndices = face.mNumIndices;

            nface.mIndices    = face.mIndices;

            face.mIndices = nullptr;

            // points and lines don't require ngon encoding (and are not supported either!)

            if (nface.mNumIndices == 3) ngonEncoder.ngonEncodeTriangle(&nface);

            continue;

        }

        // optimized code for quadrilaterals

        else if ( face.mNumIndices == 4) {

            // quads can have at maximum one concave vertex. Determine

            // this vertex (if it exists) and start tri-fanning from

            // it.

            unsigned int start_vertex = 0;

            for (unsigned int i = 0; i < 4; ++i) {

                const aiVector3D& v0 = verts[face.mIndices[(i+3) % 4]];

                const aiVector3D& v1 = verts[face.mIndices[(i+2) % 4]];

                const aiVector3D& v2 = verts[face.mIndices[(i+1) % 4]];

                const aiVector3D& v = verts[face.mIndices[i]];

                aiVector3D left = (v0-v);

                aiVector3D diag = (v1-v);

                aiVector3D right = (v2-v);

                left.Normalize();

                diag.Normalize();

                right.Normalize();

                const float angle = std::acos(left*diag) + std::acos(right*diag);

                if (angle > AI_MATH_PI_F) {

                    // this is the concave point

                    start_vertex = i;

                    break;

                }

            }

            const unsigned int temp[] = {face.mIndices[0], face.mIndices[1], face.mIndices[2], face.mIndices[3]};

            aiFace& nface = *curOut++;

            nface.mNumIndices = 3;

            nface.mIndices = face.mIndices;

            nface.mIndices[0] = temp[start_vertex];

            nface.mIndices[1] = temp[(start_vertex + 1) % 4];

            nface.mIndices[2] = temp[(start_vertex + 2) % 4];

            aiFace& sface = *curOut++;

            sface.mNumIndices = 3;

            sface.mIndices = new unsigned int[3];

            sface.mIndices[0] = temp[start_vertex];

            sface.mIndices[1] = temp[(start_vertex + 2) % 4];

            sface.mIndices[2] = temp[(start_vertex + 3) % 4];

            // prevent double deletion of the indices field

            face.mIndices = nullptr;

            ngonEncoder.ngonEncodeQuad(&nface, &sface);

            continue;

        }

        else

        {

            // A polygon with more than 3 vertices can be either concave or convex.

            // Usually everything we're getting is convex and we could easily

            // triangulate by tri-fanning. However, LightWave is probably the only

            // modeling suite to make extensive use of highly concave, monster polygons ...

            // so we need to apply the full 'ear cutting' algorithm to get it right.

            // REQUIREMENT: polygon is expected to be simple and *nearly* planar.

            // We project it onto a plane to get a 2d triangle.

            // Collect all vertices of of the polygon.

            for (unsigned int tmp = 0; tmp < num; ++tmp) {

                temp_verts3d[tmp] = verts[idx[tmp]];

            }

            // Get newell normal of the polygon. Store it for future use if it's a polygon-only mesh

            aiVector3D n;

            NewellNormal<3, 3, 3>(n, num, &temp_verts3d.front().x, &temp_verts3d.front().y, &temp_verts3d.front().z);

            if (nor_out) {

                for (unsigned int tmp = 0; tmp < num; ++tmp)

                    nor_out[idx[tmp]] = n;

            }

            // Select largest normal coordinate to ignore for projection

            const float ax = (n.x>0 ? n.x : -n.x);

            const float ay = (n.y>0 ? n.y : -n.y);

            const float az = (n.z>0 ? n.z : -n.z);

            unsigned int ac = 0, bc = 1; /* no z coord. projection to xy */

            float inv = n.z;

            if (ax > ay) {

                if (ax > az) { /* no x coord. projection to yz */

                    ac = 1; bc = 2;

                    inv = n.x;

                }

            }

            else if (ay > az) { /* no y coord. projection to zy */

                ac = 2; bc = 0;

                inv = n.y;

            }

            // Swap projection axes to take the negated projection vector into account

            if (inv < 0.f) {

                std::swap(ac,bc);

            }

            temp_verts.resize(num);

            for (unsigned int tmp = 0; tmp < num; ++tmp) {

                temp_verts[tmp].x = verts[idx[tmp]][ac];

                temp_verts[tmp].y = verts[idx[tmp]][bc];

            }

            auto indices = mapbox::earcut(temp_poly);

            for (size_t i = 0; i < indices.size(); i += 3) {

                aiFace& nface = *curOut++;

                nface.mIndices = new unsigned int[3];

                nface.mNumIndices = 3;

                nface.mIndices[0] = indices[i];

                nface.mIndices[1] = indices[i + 1];

                nface.mIndices[2] = indices[i + 2];

            }

#ifdef AI_BUILD_TRIANGULATE_DEBUG_POLYS

            // plot the plane onto which we mapped the polygon to a 2D ASCII pic

            aiVector2D bmin,bmax;

            ArrayBounds(&temp_verts[0],max,bmin,bmax);

            char grid[POLY_GRID_Y][POLY_GRID_X+POLY_GRID_XPAD];

            std::fill_n((char*)grid,POLY_GRID_Y*(POLY_GRID_X+POLY_GRID_XPAD),' ');

            for (int i =0; i < max; ++i) {

                const aiVector2D& v = (temp_verts[i] - bmin) / (bmax-bmin);

                const size_t x = static_cast<size_t>(v.x*(POLY_GRID_X-1)), y = static_cast<size_t>(v.y*(POLY_GRID_Y-1));

                char* loc = grid[y]+x;

                if (grid[y][x] != ' ') {

                    for(;*loc != ' '; ++loc);

                    *loc++ = '_';

                }

                *(loc+::ai_snprintf(loc, POLY_GRID_XPAD,"%i",i)) = ' ';

            }

            for(size_t y = 0; y < POLY_GRID_Y; ++y) {

                grid[y][POLY_GRID_X+POLY_GRID_XPAD-1] = '\0';

                fprintf(fout,"%s\n",grid[y]);

            }

            fprintf(fout,"\ntriangulation sequence: ");

#endif

        }

#ifdef AI_BUILD_TRIANGULATE_DEBUG_POLYS

        for(aiFace* f = last_face; f != curOut; ++f) {

            unsigned int* i = f->mIndices;

            fprintf(fout," (%i %i %i)",i[0],i[1],i[2]);

        }

        fprintf(fout,"\n*********************************************************************\n");

        fflush(fout);

#endif

        for(aiFace* f = last_face; f != curOut; ) {

            unsigned int* i = f->mIndices;

            i[0] = idx[i[0]];

            i[1] = idx[i[1]];

            i[2] = idx[i[2]];

            // IMPROVEMENT: Polygons are not supported yet by this ngon encoding + triangulation step.

            //              So we encode polygons as regular triangles. No way to reconstruct the original

            //              polygon in this case.

            ngonEncoder.ngonEncodeTriangle(f);

            ++f;

        }

        delete[] face.mIndices;

        face.mIndices = nullptr;

    }

#ifdef AI_BUILD_TRIANGULATE_DEBUG_POLYS

    fclose(fout);

#endif

    // kill the old faces

    delete [] pMesh->mFaces;

    // ... and store the new ones

    pMesh->mFaces    = out;

    pMesh->mNumFaces = (unsigned int)(curOut-out); /* not necessarily equal to numOut */

    return true;

}

#endif // !! ASSIMP_BUILD_NO_TRIANGULATE_PROCESS