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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>

using namespace Assimp;

// ------------------------------------------------------------------------------------------------
// Constructor to be privately used by Importer
ImproveCacheLocalityProcess::ImproveCacheLocalityProcess()
: mConfigCacheDepth(PP_ICL_PTCACHE_SIZE) {
 // empty
}

// ------------------------------------------------------------------------------------------------
// Destructor, private as well
ImproveCacheLocalityProcess::~ImproveCacheLocalityProcess() = default;

// ------------------------------------------------------------------------------------------------
// 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()) {

 unsigned int* piFIFOStack = new unsigned int[mConfigCacheDepth];
 memset(piFIFOStack,0xff,mConfigCacheDepth*sizeof(unsigned int));
 unsigned int* piCur = piFIFOStack;
 const unsigned int* const piCurEnd = piFIFOStack + mConfigCacheDepth;

 // 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);
 }
 }

 // 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
 unsigned int* const piCachingStamps = new unsigned int[pMesh->mNumVertices];
 memset(piCachingStamps,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;
 unsigned int* const piIBOutput = new unsigned int[iIdxCnt];
 unsigned int* piCSIter = piIBOutput;

 // 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);
 unsigned int* piCandidates = new unsigned int[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);
 unsigned int* piCurCandidate = piCandidates;

 // 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 ];
 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 (unsigned int* piCur = piCandidates;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 = (float)iCacheMisses / pMesh->mNumFaces;

 // very intense verbose logging ... prepare for much text if there are many meshes
 if ( DefaultLogger::get()->getLogSeverity() == Logger::VERBOSE) {
 ASSIMP_LOG_VERBOSE_DEBUG("Mesh %u | ACMR in: ", meshNum, " out: ", fACMR, " | ~", fACMR2, ((fACMR - fACMR2) / fACMR) * 100.f);
 }

 fACMR2 *= pMesh->mNumFaces;
 }
 // sort the output index buffer back to the input array
 piCSIter = piIBOutput;
 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++;
 }

 // delete temporary storage
 delete[] piCachingStamps;
 delete[] piIBOutput;
 delete[] piCandidates;

 return fACMR2;
}