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/** @file Implementation of the post processing step to improve the cache locality of a mesh.

 * <br>

 * The algorithm is roughly basing on this paper:

 * http://www.cs.princeton.edu/gfx/pubs/Sander_2007_%3ETR/tipsy.pdf

 *   .. although overdraw reduction isn't implemented yet ...

 */

// internal headers

#include "PostProcessing/ImproveCacheLocality.h"

#include "Common/VertexTriangleAdjacency.h"

#include <assimp/StringUtils.h>

#include <assimp/postprocess.h>

#include <assimp/scene.h>

#include <assimp/DefaultLogger.hpp>

#include <stdio.h>

#include <stack>

namespace Assimp {

namespace {

    ai_real calculateInputACMR(aiMesh *pMesh, const aiFace *const pcEnd,

            unsigned int configCacheDepth, unsigned int meshNum) {

        ai_real fACMR = 0.0f;

        unsigned int *piFIFOStack = new unsigned int[configCacheDepth];

        memset(piFIFOStack, 0xff, configCacheDepth * sizeof(unsigned int));

        unsigned int *piCur = piFIFOStack;

        const unsigned int *const piCurEnd = piFIFOStack + configCacheDepth;

        // count the number of cache misses

        unsigned int iCacheMisses = 0;

        for (const aiFace *pcFace = pMesh->mFaces; pcFace != pcEnd; ++pcFace) {

            for (unsigned int qq = 0; qq < 3; ++qq) {

                bool bInCache = false;

                for (unsigned int *pp = piFIFOStack; pp < piCurEnd; ++pp) {

                    if (*pp == pcFace->mIndices[qq]) {

                        // the vertex is in cache

                        bInCache = true;

                        break;

                    }

                }

                if (!bInCache) {

                    ++iCacheMisses;

                    if (piCurEnd == piCur) {

                        piCur = piFIFOStack;

                    }

                    *piCur++ = pcFace->mIndices[qq];

                }

            }

        }

        delete[] piFIFOStack;

        fACMR = (ai_real)iCacheMisses / pMesh->mNumFaces;

        if (3.0 == fACMR) {

            char szBuff[128]; // should be sufficiently large in every case

            // the JoinIdenticalVertices process has not been executed on this

            // mesh, otherwise this value would normally be at least minimally

            // smaller than 3.0 ...

            ai_snprintf(szBuff, 128, "Mesh %u: Not suitable for vcache optimization", meshNum);

            ASSIMP_LOG_WARN(szBuff);

            return static_cast<ai_real>(0.f);

        }

        return fACMR;

    }

}

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

// Constructor to be privately used by Importer

ImproveCacheLocalityProcess::ImproveCacheLocalityProcess() : mConfigCacheDepth(PP_ICL_PTCACHE_SIZE) {

    // empty

}

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

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

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

    return (pFlags & aiProcess_ImproveCacheLocality) != 0;

}

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

// Setup configuration

void ImproveCacheLocalityProcess::SetupProperties(const Importer *pImp) {

    // AI_CONFIG_PP_ICL_PTCACHE_SIZE controls the target cache size for the optimizer

    mConfigCacheDepth = pImp->GetPropertyInteger(AI_CONFIG_PP_ICL_PTCACHE_SIZE, PP_ICL_PTCACHE_SIZE);

}

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

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

void ImproveCacheLocalityProcess::Execute(aiScene *pScene) {

    if (!pScene->mNumMeshes) {

        ASSIMP_LOG_DEBUG("ImproveCacheLocalityProcess skipped; there are no meshes");

        return;

    }

    ASSIMP_LOG_DEBUG("ImproveCacheLocalityProcess begin");

    float out = 0.f;

    unsigned int numf = 0, numm = 0;

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

        const float res = ProcessMesh(pScene->mMeshes[a], a);

        if (res) {

            numf += pScene->mMeshes[a]->mNumFaces;

            out += res;

            ++numm;

        }

    }

    if (!DefaultLogger::isNullLogger()) {

        if (numf > 0) {

            ASSIMP_LOG_INFO("Cache relevant are ", numm, " meshes (", numf, " faces). Average output ACMR is ", out / numf);

        }

        ASSIMP_LOG_DEBUG("ImproveCacheLocalityProcess finished. ");

    }

}

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

// Improves the cache coherency of a specific mesh

ai_real ImproveCacheLocalityProcess::ProcessMesh(aiMesh *pMesh, unsigned int meshNum) {

    // TODO: rewrite this to use std::vector or boost::shared_array

    ai_assert(nullptr != pMesh);

    // Check whether the input data is valid

    // - there must be vertices and faces

    // - all faces must be triangulated or we can't operate on them

    if (!pMesh->HasFaces() || !pMesh->HasPositions())

        return static_cast<ai_real>(0.f);

    if (pMesh->mPrimitiveTypes != aiPrimitiveType_TRIANGLE) {

        ASSIMP_LOG_ERROR("This algorithm works on triangle meshes only");

        return static_cast<ai_real>(0.f);

    }

    if (pMesh->mNumVertices <= mConfigCacheDepth) {

        return static_cast<ai_real>(0.f);

    }

    ai_real fACMR = 3.f;

    const aiFace *const pcEnd = pMesh->mFaces + pMesh->mNumFaces;

    // Input ACMR is for logging purposes only

    if (!DefaultLogger::isNullLogger()) {

        fACMR = calculateInputACMR(pMesh, pcEnd, mConfigCacheDepth, meshNum);

    }

    // first we need to build a vertex-triangle adjacency list

    VertexTriangleAdjacency adj(pMesh->mFaces, pMesh->mNumFaces, pMesh->mNumVertices, true);

    // build a list to store per-vertex caching time stamps

    std::vector<unsigned int> piCachingStamps;

    piCachingStamps.resize(pMesh->mNumVertices);

    memset(&piCachingStamps[0], 0x0, pMesh->mNumVertices * sizeof(unsigned int));

    // allocate an empty output index buffer. We store the output indices in one large array.

    // Since the number of triangles won't change the input faces can be reused. This is how

    // we save thousands of redundant mini allocations for aiFace::mIndices

    const unsigned int iIdxCnt = pMesh->mNumFaces * 3;

    std::vector<unsigned int> piIBOutput;

    piIBOutput.resize(iIdxCnt);

    std::vector<unsigned int>::iterator piCSIter = piIBOutput.begin();

    // allocate the flag array to hold the information

    // whether a face has already been emitted or not

    std::vector<bool> abEmitted(pMesh->mNumFaces, false);

    // dead-end vertex index stack

    std::stack<unsigned int, std::vector<unsigned int>> sDeadEndVStack;

    // create a copy of the piNumTriPtr buffer

    unsigned int *const piNumTriPtr = adj.mLiveTriangles;

    const std::vector<unsigned int> piNumTriPtrNoModify(piNumTriPtr, piNumTriPtr + pMesh->mNumVertices);

    // get the largest number of referenced triangles and allocate the "candidate buffer"

    unsigned int iMaxRefTris = 0;

    {

        const unsigned int *piCur = adj.mLiveTriangles;

        const unsigned int *const piCurEnd = adj.mLiveTriangles + pMesh->mNumVertices;

        for (; piCur != piCurEnd; ++piCur) {

            iMaxRefTris = std::max(iMaxRefTris, *piCur);

        }

    }

    ai_assert(iMaxRefTris > 0);

    std::vector<unsigned int> piCandidates;

    piCandidates.resize(iMaxRefTris * 3);

    unsigned int iCacheMisses = 0;

    // ...................................................................................

    /** PSEUDOCODE for the algorithm

        A = Build-Adjacency(I) Vertex-triangle adjacency

        L = Get-Triangle-Counts(A) Per-vertex live triangle counts

        C = Zero(Vertex-Count(I)) Per-vertex caching time stamps

        D = Empty-Stack() Dead-end vertex stack

        E = False(Triangle-Count(I)) Per triangle emitted flag

        O = Empty-Index-Buffer() Empty output buffer

        f = 0 Arbitrary starting vertex

        s = k+1, i = 1 Time stamp and cursor

        while f >= 0 For all valid fanning vertices

            N = Empty-Set() 1-ring of next candidates

            for each Triangle t in Neighbors(A, f)

                if !Emitted(E,t)

                    for each Vertex v in t

                        Append(O,v) Output vertex

                        Push(D,v) Add to dead-end stack

                        Insert(N,v) Register as candidate

                        L[v] = L[v]-1 Decrease live triangle count

                        if s-C[v] > k If not in cache

                            C[v] = s Set time stamp

                            s = s+1 Increment time stamp

                    E[t] = true Flag triangle as emitted

            Select next fanning vertex

            f = Get-Next-Vertex(I,i,k,N,C,s,L,D)

        return O

        */

    // ...................................................................................

    int ivdx = 0;

    int ics = 1;

    int iStampCnt = mConfigCacheDepth + 1;

    while (ivdx >= 0) {

        unsigned int icnt = piNumTriPtrNoModify[ivdx];

        unsigned int *piList = adj.GetAdjacentTriangles(ivdx);

        std::vector<unsigned int>::iterator piCurCandidate = piCandidates.begin();

        // get all triangles in the neighborhood

        for (unsigned int tri = 0; tri < icnt; ++tri) {

            // if they have not yet been emitted, add them to the output IB

            const unsigned int fidx = *piList++;

            if (!abEmitted[fidx]) {

                // so iterate through all vertices of the current triangle

                const aiFace *pcFace = &pMesh->mFaces[fidx];

                const unsigned nind = pcFace->mNumIndices;

                for (unsigned ind = 0; ind < nind; ind++) {

                    unsigned dp = pcFace->mIndices[ind];

                    // the current vertex won't have any free triangles after this step

                    if (ivdx != (int)dp) {

                        // append the vertex to the dead-end stack

                        sDeadEndVStack.push(dp);

                        // register as candidate for the next step

                        *piCurCandidate++ = dp;

                        // decrease the per-vertex triangle counts

                        piNumTriPtr[dp]--;

                    }

                    // append the vertex to the output index buffer

                    *piCSIter++ = dp;

                    // if the vertex is not yet in cache, set its cache count

                    if (iStampCnt - piCachingStamps[dp] > mConfigCacheDepth) {

                        piCachingStamps[dp] = iStampCnt++;

                        ++iCacheMisses;

                    }

                }

                // flag triangle as emitted

                abEmitted[fidx] = true;

            }

        }

        // the vertex has now no living adjacent triangles anymore

        piNumTriPtr[ivdx] = 0;

        // get next fanning vertex

        ivdx = -1;

        int max_priority = -1;

        for (std::vector<unsigned int>::iterator piCur = piCandidates.begin(); piCur != piCurCandidate; ++piCur) {

            const unsigned int dp = *piCur;

            // must have live triangles

            if (piNumTriPtr[dp] > 0) {

                int priority = 0;

                // will the vertex be in cache, even after fanning occurs?

                unsigned int tmp;

                if ((tmp = iStampCnt - piCachingStamps[dp]) + 2 * piNumTriPtr[dp] <= mConfigCacheDepth) {

                    priority = tmp;

                }

                // keep best candidate

                if (priority > max_priority) {

                    max_priority = priority;

                    ivdx = dp;

                }

            }

        }

        // did we reach a dead end?

        if (-1 == ivdx) {

            // need to get a non-local vertex for which we have a good chance that it is still

            // in the cache ...

            while (!sDeadEndVStack.empty()) {

                unsigned int iCachedIdx = sDeadEndVStack.top();

                sDeadEndVStack.pop();

                if (piNumTriPtr[iCachedIdx] > 0) {

                    ivdx = iCachedIdx;

                    break;

                }

            }

            if (-1 == ivdx) {

                // well, there isn't such a vertex. Simply get the next vertex in input order and

                // hope it is not too bad ...

                while (ics < (int)pMesh->mNumVertices) {

                    ++ics;

                    if (piNumTriPtr[ics] > 0) {

                        ivdx = ics;

                        break;

                    }

                }

            }

        }

    }

    ai_real fACMR2 = 0.0f;

    if (!DefaultLogger::isNullLogger()) {

        fACMR2 = static_cast<ai_real>(iCacheMisses / pMesh->mNumFaces);

        const ai_real averageACMR = ((fACMR - fACMR2) / fACMR) * 100.f;

        // very intense verbose logging ... prepare for much text if there are many meshes

        if (DefaultLogger::get()->getLogSeverity() == Logger::VERBOSE) {

            ASSIMP_LOG_VERBOSE_DEBUG("Mesh ", meshNum, "| ACMR in: ", fACMR, " out: ", fACMR2, " | average ACMR ", averageACMR);

        }

        fACMR2 *= pMesh->mNumFaces;

    }

    // sort the output index buffer back to the input array

    piCSIter = piIBOutput.begin();

    for (aiFace *pcFace = pMesh->mFaces; pcFace != pcEnd; ++pcFace) {

        unsigned nind = pcFace->mNumIndices;

        unsigned *ind = pcFace->mIndices;

        if (nind > 0)

            ind[0] = *piCSIter++;

        if (nind > 1)

            ind[1] = *piCSIter++;

        if (nind > 2)

            ind[2] = *piCSIter++;

    }

    return fACMR2;

}

} // namespace Assimp