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/** @file Implementation of the VertexTriangleAdjacency helper class
 */

// internal headers
#include "VertexTriangleAdjacency.h"
#include <assimp/mesh.h>

using namespace Assimp;

// ------------------------------------------------------------------------------------------------
VertexTriangleAdjacency::VertexTriangleAdjacency(aiFace *pcFaces,
        unsigned int iNumFaces,
        unsigned int iNumVertices /*= 0*/,
        bool bComputeNumTriangles /*= false*/) {
    // compute the number of referenced vertices if it wasn't specified by the caller
    const aiFace *const pcFaceEnd = pcFaces + iNumFaces;
    if (0 == iNumVertices) {
        for (aiFace *pcFace = pcFaces; pcFace != pcFaceEnd; ++pcFace) {
            ai_assert(nullptr != pcFace);
            ai_assert(3 == pcFace->mNumIndices);
            iNumVertices = std::max(iNumVertices, pcFace->mIndices[0]);
            iNumVertices = std::max(iNumVertices, pcFace->mIndices[1]);
            iNumVertices = std::max(iNumVertices, pcFace->mIndices[2]);
        }
    }

    mNumVertices = iNumVertices + 1;

    unsigned int *pi;

    // allocate storage
    if (bComputeNumTriangles) {
        pi = mLiveTriangles = new unsigned int[iNumVertices + 1];
        ::memset(mLiveTriangles, 0, sizeof(unsigned int) * (iNumVertices + 1));
        mOffsetTable = new unsigned int[iNumVertices + 2] + 1;
    } else {
        pi = mOffsetTable = new unsigned int[iNumVertices + 2] + 1;
        ::memset(mOffsetTable, 0, sizeof(unsigned int) * (iNumVertices + 1));
        mLiveTriangles = nullptr; // important, otherwise the d'tor would crash
    }

    // get a pointer to the end of the buffer
    unsigned int *piEnd = pi + iNumVertices;
    *piEnd++ = 0u;

    // first pass: compute the number of faces referencing each vertex
    for (aiFace *pcFace = pcFaces; pcFace != pcFaceEnd; ++pcFace) {
        unsigned nind = pcFace->mNumIndices;
        unsigned *ind = pcFace->mIndices;
        if (nind > 0) pi[ind[0]]++;
        if (nind > 1) pi[ind[1]]++;
        if (nind > 2) pi[ind[2]]++;
    }

    // second pass: compute the final offset table
    unsigned int iSum = 0;
    unsigned int *piCurOut = this->mOffsetTable;
    for (unsigned int *piCur = pi; piCur != piEnd; ++piCur, ++piCurOut) {

        unsigned int iLastSum = iSum;
        iSum += *piCur;
        *piCurOut = iLastSum;
    }
    pi = this->mOffsetTable;

    // third pass: compute the final table
    this->mAdjacencyTable = new unsigned int[iSum];
    iSum = 0;
    for (aiFace *pcFace = pcFaces; pcFace != pcFaceEnd; ++pcFace, ++iSum) {
        unsigned nind = pcFace->mNumIndices;
        unsigned *ind = pcFace->mIndices;

        if (nind > 0) mAdjacencyTable[pi[ind[0]]++] = iSum;
        if (nind > 1) mAdjacencyTable[pi[ind[1]]++] = iSum;
        if (nind > 2) mAdjacencyTable[pi[ind[2]]++] = iSum;
    }
    // fourth pass: undo the offset computations made during the third pass
    // We could do this in a separate buffer, but this would be TIMES slower.
    --mOffsetTable;
    *mOffsetTable = 0u;
}
// ------------------------------------------------------------------------------------------------
VertexTriangleAdjacency::~VertexTriangleAdjacency() {
    // delete allocated storage
    delete[] mOffsetTable;
    delete[] mAdjacencyTable;
    delete[] mLiveTriangles;
}
