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/** @file  FindDegenerates.cpp

 *  @brief Implementation of the FindDegenerates post-process step.

 */

#include "FindDegenerates.h"

#include "Geometry/GeometryUtils.h"

#include "ProcessHelper.h"

#include <assimp/Exceptional.h>

#include <unordered_map>

using namespace Assimp;

// Correct node indices to meshes and remove references to deleted mesh

static void updateSceneGraph(aiNode *pNode, const std::unordered_map<unsigned int, unsigned int> &meshMap);

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

// Constructor to be privately used by Importer

FindDegeneratesProcess::FindDegeneratesProcess() :

        mConfigRemoveDegenerates(false),

        mConfigCheckAreaOfTriangle(false) {

    // empty

}

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

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

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

    return 0 != (pFlags & aiProcess_FindDegenerates);

}

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

// Setup import configuration

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

    // Get the current value of AI_CONFIG_PP_FD_REMOVE

    mConfigRemoveDegenerates = (0 != pImp->GetPropertyInteger(AI_CONFIG_PP_FD_REMOVE, 0));

    mConfigCheckAreaOfTriangle = (0 != pImp->GetPropertyInteger(AI_CONFIG_PP_FD_CHECKAREA));

}

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

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

void FindDegeneratesProcess::Execute(aiScene *pScene) {

    ASSIMP_LOG_DEBUG("FindDegeneratesProcess begin");

    if (nullptr == pScene) {

        return;

    }

    std::unordered_map<unsigned int, unsigned int> meshMap;

    meshMap.reserve(pScene->mNumMeshes);

    const unsigned int originalNumMeshes = pScene->mNumMeshes;

    unsigned int targetIndex = 0;

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

        // Do not process point cloud, ExecuteOnMesh works only with faces data

        if ((pScene->mMeshes[i]->mPrimitiveTypes != aiPrimitiveType::aiPrimitiveType_POINT) && ExecuteOnMesh(pScene->mMeshes[i])) {

            delete pScene->mMeshes[i];

            // Not strictly required, but clean:

            pScene->mMeshes[i] = nullptr;

        } else {

            meshMap[i] = targetIndex;

            pScene->mMeshes[targetIndex] = pScene->mMeshes[i];

            ++targetIndex;

        }

    }

    pScene->mNumMeshes = targetIndex;

    if (meshMap.size() < originalNumMeshes) {

        updateSceneGraph(pScene->mRootNode, meshMap);

    }

    ASSIMP_LOG_DEBUG("FindDegeneratesProcess finished");

}

static void updateSceneGraph(aiNode *pNode, const std::unordered_map<unsigned int, unsigned int> &meshMap) {

    unsigned int targetIndex = 0;

    for (unsigned i = 0; i < pNode->mNumMeshes; ++i) {

        const unsigned int sourceMeshIndex = pNode->mMeshes[i];

        auto it = meshMap.find(sourceMeshIndex);

        if (it != meshMap.end()) {

            pNode->mMeshes[targetIndex] = it->second;

            ++targetIndex;

        }

    }

    pNode->mNumMeshes = targetIndex;

    // recurse to all children

    for (unsigned i = 0; i < pNode->mNumChildren; ++i) {

        updateSceneGraph(pNode->mChildren[i], meshMap);

    }

}

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

// Executes the post processing step on the given imported mesh

bool FindDegeneratesProcess::ExecuteOnMesh(aiMesh *mesh) {

    mesh->mPrimitiveTypes = 0;

    std::vector<bool> remove_me;

    if (mConfigRemoveDegenerates) {

        remove_me.resize(mesh->mNumFaces, false);

    }

    unsigned int deg = 0, limit;

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

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

        bool first = true;

        auto vertex_in_range = [numVertices = mesh->mNumVertices](unsigned int vertex_idx) { return vertex_idx < numVertices; };

        // check whether the face contains degenerated entries

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

            if (!std::all_of(face.mIndices, face.mIndices + face.mNumIndices, vertex_in_range))

                continue;

            // Polygons with more than 4 points are allowed to have double points, that is

            // simulating polygons with holes just with concave polygons. However,

            // double points may not come directly after another.

            limit = face.mNumIndices;

            if (face.mNumIndices > 4) {

                limit = std::min(limit, i + 2);

            }

            for (unsigned int t = i + 1; t < limit; ++t) {

                if (mesh->mVertices[face.mIndices[i]] == mesh->mVertices[face.mIndices[t]]) {

                    // we have found a matching vertex position

                    // remove the corresponding index from the array

                    --face.mNumIndices;

                    --limit;

                    for (unsigned int m = t; m < face.mNumIndices; ++m) {

                        face.mIndices[m] = face.mIndices[m + 1];

                    }

                    --t;

                    // NOTE: we set the removed vertex index to an unique value

                    // to make sure the developer gets notified when his

                    // application attempts to access this data.

                    face.mIndices[face.mNumIndices] = 0xdeadbeef;

                    if (first) {

                        ++deg;

                        first = false;

                    }

                    if (mConfigRemoveDegenerates) {

                        remove_me[a] = true;

                        goto evil_jump_outside; // hrhrhrh ... yeah, this rocks baby!

                    }

                }

            }

            if (mConfigCheckAreaOfTriangle) {

                if (face.mNumIndices == 3) {

                    ai_real area = GeometryUtils::calculateAreaOfTriangle(face, mesh);

                    if (area < ai_epsilon) {

                        if (mConfigRemoveDegenerates) {

                            remove_me[a] = true;

                            ++deg;

                            goto evil_jump_outside;

                        }

                        // todo: check for index which is corrupt.

                    }

                }

            }

        }

        // We need to update the primitive flags array of the mesh.

        switch (face.mNumIndices) {

        case 1u:

            mesh->mPrimitiveTypes |= aiPrimitiveType_POINT;

            break;

        case 2u:

            mesh->mPrimitiveTypes |= aiPrimitiveType_LINE;

            break;

        case 3u:

            mesh->mPrimitiveTypes |= aiPrimitiveType_TRIANGLE;

            break;

        default:

            mesh->mPrimitiveTypes |= aiPrimitiveType_POLYGON;

            break;

        };

    evil_jump_outside:

        continue;

    }

    // If AI_CONFIG_PP_FD_REMOVE is true, remove degenerated faces from the import

    if (mConfigRemoveDegenerates && deg) {

        unsigned int n = 0;

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

            aiFace &face_src = mesh->mFaces[a];

            if (!remove_me[a]) {

                aiFace &face_dest = mesh->mFaces[n++];

                // Do a manual copy, keep the index array

                face_dest.mNumIndices = face_src.mNumIndices;

                face_dest.mIndices = face_src.mIndices;

                if (&face_src != &face_dest) {

                    // clear source

                    face_src.mNumIndices = 0;

                    face_src.mIndices = nullptr;

                }

            } else {

                // Otherwise delete it if we don't need this face

                delete[] face_src.mIndices;

                face_src.mIndices = nullptr;

                face_src.mNumIndices = 0;

            }

        }

        // Just leave the rest of the array unreferenced, we don't care for now

        mesh->mNumFaces = n;

        if (!mesh->mNumFaces) {

            // The whole mesh consists of degenerated faces

            // signal upward, that this mesh should be deleted.

            ASSIMP_LOG_VERBOSE_DEBUG("FindDegeneratesProcess removed a mesh full of degenerated primitives");

            return true;

        }

    }

    if (deg && !DefaultLogger::isNullLogger()) {

        ASSIMP_LOG_WARN("Found ", deg, " degenerated primitives");

    }

    return false;

}