// Gmsh - Copyright (C) 1997-2025 C. Geuzaine, J.-F. Remacle
//
// See the LICENSE.txt file in the Gmsh root directory for license information.
// Please report all issues on https://gitlab.onelab.info/gmsh/gmsh/issues.
//
// Contributor(s):
//   Anthony Royer

#include <cstdio>
#include <fstream>
#include <vector>
#include <map>
#include <algorithm>
#include <sstream>
#include <string>
#include <cstdlib>
#include <limits>
#include <stdexcept>

#include "GmshDefines.h"
#include "OS.h"
#include "Context.h"
#include "GModel.h"
#include "GEntity.h"
#include "partitionRegion.h"
#include "partitionFace.h"
#include "partitionEdge.h"
#include "partitionVertex.h"
#include "discreteEdge.h"
#include "ghostFace.h"
#include "ghostEdge.h"
#include "ghostRegion.h"
#include "MPoint.h"
#include "MLine.h"
#include "MTriangle.h"
#include "MQuadrangle.h"
#include "MTetrahedron.h"
#include "MHexahedron.h"
#include "MPrism.h"
#include "MPyramid.h"
#include "MTrihedron.h"
#include "StringUtils.h"

#if defined(HAVE_POST)
#include "PView.h"
#endif

static bool readMSH4Physicals(GModel *const model, FILE *fp,
                              GEntity *const entity, bool binary,
                              bool swap)
{
  std::size_t numPhy = 0;
  if(binary) {
    if(fread(&numPhy, sizeof(std::size_t), 1, fp) != 1) { return false; }
    if(swap) SwapBytes((char *)&numPhy, sizeof(std::size_t), 1);

    std::vector<int> phyTags(numPhy);
    if(fread(&phyTags[0], sizeof(int), numPhy, fp) != numPhy) { return false; }
    if(swap) SwapBytes((char *)&phyTags[0], sizeof(int), numPhy);

    for(std::size_t i = 0; i < numPhy; i++) {
      entity->addPhysicalEntity(phyTags[i]);
    }
  }
  else {
    if(fscanf(fp, "%zu", &numPhy) != 1){ return false; }
    for(std::size_t i = 0; i < numPhy; i++) {
      int phyTag = 0;
      if(fscanf(fp, "%d", &phyTag) != 1) { return false; }
      entity->addPhysicalEntity(phyTag);
    }
  }
  return true;
}

static bool readMSH4BoundingEntities(GModel *const model, FILE *fp,
                                     GEntity *const entity, bool binary,
                                     bool swap, int maxTagEmbed)
{
  std::size_t numBrep = 0;
  std::vector<GEntity *> boundingEntities, embeddedEntities;
  std::vector<int> boundingSign;

  if(binary) {
    if(fread(&numBrep, sizeof(std::size_t), 1, fp) != 1) { return false; }
    if(swap) SwapBytes((char *)&numBrep, sizeof(std::size_t), 1);

    std::vector<int> brepTags(numBrep);
    if(fread(&brepTags[0], sizeof(int), numBrep, fp) != numBrep) {
      return false;
    }
    if(swap) SwapBytes((char *)&brepTags[0], sizeof(int), numBrep);

    for(std::size_t i = 0; i < numBrep; i++) {
      GEntity *brep =
        model->getEntityByTag(entity->dim() - 1, std::abs(brepTags[i]));
      if(!brep) {
        Msg::Warning("Entity %d not found in the Brep of entity %d",
                     brepTags[i], entity->tag());
      }
      else {
        boundingEntities.push_back(brep);
        boundingSign.push_back((std::abs(brepTags[i]) == brepTags[i] ? 1 : -1));
      }
    }
  }
  else {
    if(fscanf(fp, "%zu", &numBrep) != 1) { return false; }
    for(std::size_t i = 0; i < numBrep; i++) {
      int entityTag = 0;
      if(fscanf(fp, "%d", &entityTag) != 1) { return false; }

      // FIXME: temporary hack until we update the MSH4 format - assume entities
      // with tag > maxTagEmbed are embedded entities of dimension (dim - 1);
      // this does not work for e.g. points in surfaces (dimension == dim - 2)
      if (std::abs(entityTag) > maxTagEmbed){
        int embeddedTag = std::abs(entityTag) - maxTagEmbed;
	GEntity *emb = model->getEntityByTag(entity->dim() - 1, embeddedTag);
	if(!emb) {
	  Msg::Warning("Embedded entity %d not found in the Brep of entity %d",
                       embeddedTag, entity->tag());
	}
	else {
	  embeddedEntities.push_back(emb);
	}
      }
      else {
	GEntity *brep =
	  model->getEntityByTag(entity->dim() - 1, std::abs(entityTag));
	if(!brep) {
	  Msg::Warning("Entity %d not found in the Brep of entity %d", entityTag,
		       entity->tag());
	}
	else {
	  boundingEntities.push_back(brep);
	  boundingSign.push_back((std::abs(entityTag) == entityTag ? 1 : -1));
	}
      }
    }
  }

  switch(entity->dim()) {
  case 1:
    if(boundingEntities.size() == 2) {
      reinterpret_cast<GEdge *>(entity)->setBeginVertex(
        reinterpret_cast<GVertex *>(boundingEntities[0]));
      reinterpret_cast<GEdge *>(entity)->setEndVertex(
        reinterpret_cast<GVertex *>(boundingEntities[1]));
    }
    else if(boundingEntities.size() == 1) {
      if(boundingSign[0] == 1) {
        reinterpret_cast<GEdge *>(entity)->setBeginVertex(
          reinterpret_cast<GVertex *>(boundingEntities[0]));
      }
      else {
        reinterpret_cast<GEdge *>(entity)->setEndVertex(
          reinterpret_cast<GVertex *>(boundingEntities[0]));
      }
    }
    break;
  case 2: {
    std::vector<int> tags(boundingEntities.size());
    for(std::size_t i = 0; i < boundingEntities.size(); i++)
      tags[i] = std::abs(boundingEntities[i]->tag());
    reinterpret_cast<GFace *>(entity)->setBoundEdges(tags, boundingSign);
    for(std::size_t i = 0; i < embeddedEntities.size(); i++){
      reinterpret_cast<GFace *>(entity)->addEmbeddedEdge
        (reinterpret_cast<GEdge *>(embeddedEntities[i]));
    }
  } break;
  case 3: {
    std::vector<int> tags(boundingEntities.size());
    for(std::size_t i = 0; i < boundingEntities.size(); i++)
      tags[i] = std::abs(boundingEntities[i]->tag());
    reinterpret_cast<GRegion *>(entity)->setBoundFaces(tags, boundingSign);
  } break;
  default: break;
  }
  return true;
}

static bool readMSH4EntityInfo(FILE *fp, bool binary,
                               bool swap, double version, bool partition,
                               int dim, int &tag, int &parentDim,
                               int &parentTag, std::vector<int> &partitions,
                               double &minX, double &minY, double &minZ,
                               double &maxX, double &maxY, double &maxZ)
{
  if(partition) {
    if(binary) {
      int dataInt[3];
      if(fread(dataInt, sizeof(int), 3, fp) != 3) { return false; }
      if(swap) SwapBytes((char *)dataInt, sizeof(int), 3);
      tag = dataInt[0];
      parentDim = dataInt[1];
      parentTag = dataInt[2];
      std::size_t numPart;
      if(fread(&numPart, sizeof(std::size_t), 1, fp) != 1) { return false; }
      partitions.resize(numPart, 0);
      if(fread(&partitions[0], sizeof(int), numPart, fp) != numPart) {
        return false;
      }
      if(swap) SwapBytes((char *)&partitions[0], sizeof(int), numPart);
      double dataDouble[6];
      const std::size_t nbb = (dim > 0) ? 6 : 3;
      if(fread(dataDouble, sizeof(double), nbb, fp) != nbb) { return false; }
      if(swap) SwapBytes((char *)dataDouble, sizeof(double), nbb);
      minX = dataDouble[0];
      minY = dataDouble[1];
      minZ = dataDouble[2];
      maxX = dataDouble[(nbb == 6) ? 3 : 0];
      maxY = dataDouble[(nbb == 6) ? 4 : 1];
      maxZ = dataDouble[(nbb == 6) ? 5 : 2];
    }
    else {
      std::size_t numPart = 0;
      if(fscanf(fp, "%d %d %d %zu", &tag, &parentDim, &parentTag, &numPart) !=
         4) {
        return false;
      }
      partitions.resize(numPart, 0);
      for(std::size_t i = 0; i < numPart; i++) {
        if(fscanf(fp, "%d", &partitions[i]) != 1) { return false; }
      }
      if(version < 4.1 || dim > 0) {
        if(fscanf(fp, "%lf %lf %lf %lf %lf %lf", &minX, &minY, &minZ, &maxX,
                  &maxY, &maxZ) != 6) {
          return false;
        }
      }
      else {
        if(fscanf(fp, "%lf %lf %lf", &minX, &minY, &minZ) != 3) {
          return false;
        }
        maxX = minX;
        maxY = minY;
        maxZ = minZ;
      }
    }
  }
  else {
    if(binary) {
      int dataInt;
      if(fread(&dataInt, sizeof(int), 1, fp) != 1) { return false; }
      if(swap) SwapBytes((char *)&dataInt, sizeof(int), 1);
      double dataDouble[6];
      const std::size_t nbb = (dim > 0) ? 6 : 3;
      if(fread(dataDouble, sizeof(double), nbb, fp) != nbb) { return false; }
      if(swap) SwapBytes((char *)dataDouble, sizeof(double), nbb);
      tag = dataInt;
      minX = dataDouble[0];
      minY = dataDouble[1];
      minZ = dataDouble[2];
      maxX = dataDouble[(nbb == 6) ? 3 : 0];
      maxY = dataDouble[(nbb == 6) ? 4 : 1];
      maxZ = dataDouble[(nbb == 6) ? 5 : 2];
    }
    else {
      if(version < 4.1 || dim > 0) {
        if(fscanf(fp, "%d %lf %lf %lf %lf %lf %lf", &tag, &minX, &minY, &minZ,
                  &maxX, &maxY, &maxZ) != 7) {
          return false;
        }
      }
      else {
        if(fscanf(fp, "%d %lf %lf %lf", &tag, &minX, &minY, &minZ) != 4) {
          return false;
        }
        maxX = minX;
        maxY = minY;
        maxZ = minZ;
      }
    }
  }
  return true;
}

static bool readMSH4Entities(GModel *const model, FILE *fp, bool partition,
                             bool binary, bool swap, double version)
{
  if(partition) {
    std::size_t numPartitions = 0;
    std::size_t ghostSize = 0;
    std::vector<int> ghostTags;

    if(binary) {
      if(fread(&numPartitions, sizeof(std::size_t), 1, fp) != 1) {
        return false;
      }
      if(swap) SwapBytes((char *)&numPartitions, sizeof(std::size_t), 1);

      if(fread(&ghostSize, sizeof(std::size_t), 1, fp) != 1) { return false; }
      if(swap) SwapBytes((char *)&ghostSize, sizeof(std::size_t), 1);
      if(ghostSize) {
        ghostTags.resize(2 * ghostSize);
        if(fread(&ghostTags[0], sizeof(int), 2 * ghostSize, fp) !=
           2 * ghostSize) {
          return false;
        }
        if(swap) SwapBytes((char *)&ghostTags[0], sizeof(int), 2 * ghostSize);
      }
    }
    else {
      if(fscanf(fp, "%zu", &numPartitions) != 1) { return false; }
      if(fscanf(fp, "%zu", &ghostSize) != 1) { return false; }
      if(ghostSize) {
        ghostTags.resize(2 * ghostSize);
        for(std::size_t i = 0; i < 2 * ghostSize; i += 2) {
          if(fscanf(fp, "%d %d", &ghostTags[i], &ghostTags[i + 1]) != 2) {
            return false;
          }
        }
      }
    }

    model->setNumPartitions(numPartitions);
    Msg::Info("%zu partitions", model->getNumPartitions());
    for(std::size_t i = 0; i < 2 * ghostSize; i += 2) {
      switch(model->getDim()) {
      case 1: {
        ghostEdge *ghostEntities =
          new ghostEdge(model, ghostTags[i], ghostTags[i + 1]);
        model->add(ghostEntities);
      } break;
      case 2: {
        ghostFace *ghostEntities =
          new ghostFace(model, ghostTags[i], ghostTags[i + 1]);
        model->add(ghostEntities);
      } break;
      case 3: {
        ghostRegion *ghostEntities =
          new ghostRegion(model, ghostTags[i], ghostTags[i + 1]);
        model->add(ghostEntities);
      } break;
      default: break;
      }
    }
  }

  std::size_t numEntities[4] = {0, 0, 0, 0};
  if(binary) {
    if(fread(numEntities, sizeof(std::size_t), 4, fp) != 4) { return false; }
    if(swap) SwapBytes((char *)numEntities, sizeof(std::size_t), 4);
  }
  else {
    if(fscanf(fp, "%zu %zu %zu %zu", &numEntities[0], &numEntities[1],
              &numEntities[2], &numEntities[3]) != 4) {
      return false;
    }
  }

  int nume = numEntities[0] + numEntities[1] + numEntities[2] + numEntities[3];
  if(partition)
    Msg::Info("%d partition entit%s", nume, nume > 1 ? "ies" : "y");
  else
    Msg::Info("%d entit%s", nume, nume > 1 ? "ies" : "y");

  // FIXME: remove this when embedded entities are correctly handled
  int maxTags[3] = {0, 0, 0};

  for(int dim = 0; dim < 4; dim++) {
    for(std::size_t i = 0; i < numEntities[dim]; i++) {
      int tag = 0, parentDim = 0, parentTag = 0;
      std::vector<int> partitions;
      double minX = 0., minY = 0., minZ = 0., maxX = 0., maxY = 0., maxZ = 0.;
      if(!readMSH4EntityInfo(fp, binary, swap, version, partition,
                             dim, tag, parentDim, parentTag, partitions, minX,
                             minY, minZ, maxX, maxY, maxZ)) {
        return false;
      }

      switch(dim) {
      case 0: {
        GVertex *gv = model->getVertexByTag(tag);
        if(!gv) {
          if(partition) {
            gv = new partitionVertex(model, tag, partitions);
            if(parentTag)
              static_cast<partitionVertex *>(gv)->setParentEntity(
                model->getEntityByTag(parentDim, parentTag));
          }
          else {
            gv = new discreteVertex(model, tag, minX, minY, minZ);
          }
          model->add(gv);
        }
        if(!readMSH4Physicals(model, fp, gv, binary, swap)) {
          return false;
        }
      } break;
      case 1: {
        GEdge *ge = model->getEdgeByTag(tag);
        if(!ge) {
          if(partition) {
            ge = new partitionEdge(model, tag, nullptr, nullptr, partitions);
            if(parentTag)
              static_cast<partitionEdge *>(ge)->setParentEntity(
                model->getEntityByTag(parentDim, parentTag));
          }
          else {
            ge = new discreteEdge(model, tag, nullptr, nullptr);
          }
          model->add(ge);
        }
        if(!readMSH4Physicals(model, fp, ge, binary, swap)) {
          return false;
        }
        if(!readMSH4BoundingEntities(model, fp, ge, binary, swap, maxTags[0])) {
          return false;
        }
      } break;
      case 2: {
        GFace *gf = model->getFaceByTag(tag);
        if(!gf) {
          if(partition) {
            gf = new partitionFace(model, tag, partitions);
            if(parentTag)
              static_cast<partitionFace *>(gf)->setParentEntity(
                model->getEntityByTag(parentDim, parentTag));
          }
          else {
            gf = new discreteFace(model, tag);
          }
          model->add(gf);
        }
        if(!readMSH4Physicals(model, fp, gf, binary, swap)) {
          return false;
        }
        if(!readMSH4BoundingEntities(model, fp, gf, binary, swap, maxTags[1])) {
          return false;
        }
      } break;
      case 3: {
        GRegion *gr = model->getRegionByTag(tag);
        if(!gr) {
          if(partition) {
            gr = new partitionRegion(model, tag, partitions);
            if(parentTag)
              static_cast<partitionRegion *>(gr)->setParentEntity(
                model->getEntityByTag(parentDim, parentTag));
          }
          else {
            gr = new discreteRegion(model, tag);
          }
          model->add(gr);
        }
        if(!readMSH4Physicals(model, fp, gr, binary, swap)) {
          return false;
        }
        if(!readMSH4BoundingEntities(model, fp, gr, binary, swap, maxTags[2])) {
          return false;
        }
      } break;
      }
    }

    // FIXME: remove this when embedded entities are correctly handled
    if(dim < 3) maxTags[dim] = model->getMaxElementaryNumber(dim);
  }
  return true;
}

static std::pair<std::size_t, MVertex *> *
readMSH4Nodes(GModel *const model, FILE *fp, bool binary, bool &dense,
              std::size_t &totalNumNodes, std::size_t &maxNodeNum, bool swap,
              double version)
{
  std::size_t numBlock = 0, minTag = 0, maxTag = 0;
  totalNumNodes = 0;
  maxNodeNum = 0;

  if(binary) {
    std::size_t data[4];
    if(fread(data, sizeof(std::size_t), 4, fp) != 4) { return nullptr; }
    if(swap) SwapBytes((char *)data, sizeof(std::size_t), 4);
    numBlock = data[0];
    totalNumNodes = data[1];
    minTag = data[2];
    maxTag = data[3];
  }
  else {
    if(version >= 4.1) {
      if(fscanf(fp, "%zu %zu %zu %zu", &numBlock, &totalNumNodes, &minTag,
                &maxTag) != 4) {
        return nullptr;
      }
    }
    else {
      if(fscanf(fp, "%zu %zu", &numBlock, &totalNumNodes) != 2) {
        return nullptr;
      }
    }
  }

  std::size_t nodeRead = 0;
  std::size_t minNodeNum = std::numeric_limits<std::size_t>::max();

  std::pair<std::size_t, MVertex *> *vertexCache =
    new std::pair<std::size_t, MVertex *>[totalNumNodes];

  Msg::Info("%zu node%s", totalNumNodes, totalNumNodes > 1 ? "s" : "");
  Msg::StartProgressMeter(totalNumNodes);

  for(std::size_t i = 0; i < numBlock; i++) {
    int parametric = 0;
    int entityTag = 0, entityDim = 0;
    std::size_t numNodes = 0;

    if(binary) {
      int data[3];
      if(fread(data, sizeof(int), 3, fp) != 3) {
        delete[] vertexCache;
        return nullptr;
      }
      if(swap) SwapBytes((char *)data, sizeof(int), 3);
      entityDim = data[0];
      entityTag = data[1];
      parametric = data[2];

      if(fread(&numNodes, sizeof(std::size_t), 1, fp) != 1) {
        delete[] vertexCache;
        return nullptr;
      }
      if(swap) SwapBytes((char *)&numNodes, sizeof(std::size_t), 1);
    }
    else {
      if(version >= 4.1) {
        if(fscanf(fp, "%d %d %d %zu", &entityDim, &entityTag, &parametric,
                  &numNodes) != 4) {
          delete[] vertexCache;
          return nullptr;
        }
      }
      else {
        if(fscanf(fp, "%d %d %d %zu", &entityTag, &entityDim, &parametric,
                  &numNodes) != 4) {
          delete[] vertexCache;
          return nullptr;
        }
      }
    }

    GEntity *entity = model->getEntityByTag(entityDim, entityTag);
    if(!entity) {
      switch(entityDim) {
      case 0: {
        Msg::Info("Creating discrete point %d", entityTag);
        GVertex *gv = new discreteVertex(model, entityTag);
        GModel::current()->add(gv);
        entity = gv;
        break;
      }
      case 1: {
        Msg::Info("Creating discrete curve %d", entityTag);
        GEdge *ge = new discreteEdge(model, entityTag, nullptr, nullptr);
        GModel::current()->add(ge);
        entity = ge;
        break;
      }
      case 2: {
        Msg::Info("Creating discrete surface %d", entityTag);
        GFace *gf = new discreteFace(model, entityTag);
        GModel::current()->add(gf);
        entity = gf;
        break;
      }
      case 3: {
        Msg::Info("Creating discrete volume %d", entityTag);
        GRegion *gr = new discreteRegion(model, entityTag);
        GModel::current()->add(gr);
        entity = gr;
        break;
      }
      default: {
        Msg::Error("Invalid dimension %d to create discrete entity", entityDim);
        delete[] vertexCache;
        return nullptr;
      }
      }
    }

    std::size_t n = 3;
    if(parametric) n += entityDim;

    std::vector<std::size_t> tags(numNodes);
    if(binary) {
      if(fread(&tags[0], sizeof(std::size_t), numNodes, fp) != numNodes) {
        delete[] vertexCache;
        return nullptr;
      }
      if(swap) SwapBytes((char *)&tags[0], sizeof(std::size_t), numNodes);
      std::vector<double> coord(n * numNodes);
      if(fread(&coord[0], sizeof(double), n * numNodes, fp) != n * numNodes) {
        delete[] vertexCache;
        return nullptr;
      }
      if(swap) SwapBytes((char *)&coord[0], sizeof(double), n * numNodes);
      std::size_t k = 0;
      for(std::size_t j = 0; j < numNodes; j++) {
        MVertex *mv = nullptr;
        std::size_t tagNode = tags[j];
        if(n == 5) {
          mv = new MFaceVertex(coord[k], coord[k + 1], coord[k + 2], entity,
                               coord[k + 3], coord[k + 4], tagNode);
        }
        else if(n == 4) {
          mv = new MEdgeVertex(coord[k], coord[k + 1], coord[k + 2], entity,
                               coord[k + 3], tagNode);
        }
        else {
          mv =
            new MVertex(coord[k], coord[k + 1], coord[k + 2], entity, tagNode);
        }
        k += n;
        entity->addMeshVertex(mv);
        mv->setEntity(entity);
        minNodeNum = std::min(minNodeNum, tagNode);
        maxNodeNum = std::max(maxNodeNum, tagNode);
        vertexCache[nodeRead] = std::make_pair(tagNode, mv);
        nodeRead++;
        if(totalNumNodes > 100000)
          Msg::ProgressMeter(nodeRead, true, "Reading nodes");
      }
    }
    else {
      if(version >= 4.1) {
        for(std::size_t j = 0; j < numNodes; j++) {
          if(fscanf(fp, "%zu", &tags[j]) != 1) {
            delete[] vertexCache;
            return nullptr;
          }
        }
      }
      for(std::size_t j = 0; j < numNodes; j++) {
        std::size_t tagNode = 0;
        if(version >= 4.1) { tagNode = tags[j]; }
        else {
          if(fscanf(fp, "%zu", &tagNode) != 1) {
            delete[] vertexCache;
            return nullptr;
          }
        }
        MVertex *mv = nullptr;
        if(n == 5) {
          double x, y, z, u, v;
          if(fscanf(fp, "%lf %lf %lf %lf %lf", &x, &y, &z, &u, &v) != 5) {
            delete[] vertexCache;
            return nullptr;
          }
          mv = new MFaceVertex(x, y, z, entity, u, v, tagNode);
        }
        else if(n == 4) {
          double x, y, z, u;
          if(fscanf(fp, "%lf %lf %lf %lf", &x, &y, &z, &u) != 4) {
            delete[] vertexCache;
            return nullptr;
          }
          mv = new MEdgeVertex(x, y, z, entity, u, tagNode);
        }
        else {
          double x, y, z;
          if(fscanf(fp, "%lf %lf %lf", &x, &y, &z) != 3) {
            delete[] vertexCache;
            return nullptr;
          }
          // discard extra parametric coordinates, as Gmsh does not use them
          for(std::size_t k = 3; k < n; k++) {
            double dummy;
            if(fscanf(fp, "%lf", &dummy) != 1) {
              delete[] vertexCache;
              return nullptr;
            }
          }
          mv = new MVertex(x, y, z, entity, tagNode);
        }
        entity->addMeshVertex(mv);
        mv->setEntity(entity);
        minNodeNum = std::min(minNodeNum, tagNode);
        maxNodeNum = std::max(maxNodeNum, tagNode);
        vertexCache[nodeRead] = std::make_pair(tagNode, mv);
        nodeRead++;
        if(totalNumNodes > 100000)
          Msg::ProgressMeter(nodeRead, true, "Reading nodes");
      }
    }
  }

  if(version >= 4.1) { // consistency check
    if(minTag != minNodeNum || maxTag != maxNodeNum)
      Msg::Warning("Min/Max node tags reported in section header are wrong: "
                   "(%d/%d) != (%d/%d)",
                   minTag, maxTag, minNodeNum, maxNodeNum);
  }

  // if the vertex numbering is (fairly) dense, we fill the vector cache,
  // otherwise we fill the map cache
  if(minNodeNum == 1 && maxNodeNum == totalNumNodes) {
    Msg::Debug("Vertex numbering is dense");
    dense = true;
  }
  else if(maxNodeNum < 10 * totalNumNodes) {
    Msg::Debug(
      "Vertex numbering is fairly dense - still caching with a vector");
    dense = true;
  }
  else {
    Msg::Debug("Vertex numbering is not dense");
    dense = false;
  }

  return vertexCache;
}

static std::pair<std::size_t, std::pair<MElement *, int> > *
readMSH4Elements(GModel *const model, FILE *fp, bool binary, bool &dense,
                 std::size_t &totalNumElements, std::size_t &maxElementNum,
                 bool swap, double version)
{
  char str[10000]; // 1000 nodes for order 9 hex, 10 digits each
  std::size_t numBlock = 0, minTag = 0, maxTag = 0;
  totalNumElements = 0;
  maxElementNum = 0;

  if(binary) {
    std::size_t data[4];
    if(fread(data, sizeof(std::size_t), 4, fp) != 4) { return nullptr; }
    if(swap) SwapBytes((char *)data, sizeof(std::size_t), 4);
    numBlock = data[0];
    totalNumElements = data[1];
    minTag = data[2];
    maxTag = data[3];
  }
  else {
    if(version >= 4.1) {
      if(fscanf(fp, "%zu %zu %zu %zu", &numBlock, &totalNumElements, &minTag,
                &maxTag) != 4) {
        return nullptr;
      }
    }
    else {
      if(fscanf(fp, "%zu %zu", &numBlock, &totalNumElements) != 2) {
        return nullptr;
      }
    }
  }

  std::size_t elementRead = 0;
  std::size_t minElementNum = std::numeric_limits<std::size_t>::max();

  std::pair<std::size_t, std::pair<MElement *, int> > *elementCache =
    new std::pair<std::size_t, std::pair<MElement *, int> >[totalNumElements];
  Msg::Info("%zu element%s", totalNumElements, totalNumElements > 1 ? "s" : "");
  Msg::StartProgressMeter(totalNumElements);

  for(std::size_t i = 0; i < numBlock; i++) {
    int entityTag = 0, entityDim = 0, elmType = 0;
    std::size_t numElements = 0;

    if(binary) {
      int data[3];
      if(fread(data, sizeof(int), 3, fp) != 3) {
        delete[] elementCache;
        return nullptr;
      }
      if(swap) SwapBytes((char *)data, sizeof(int), 3);
      entityDim = data[0];
      entityTag = data[1];
      elmType = data[2];

      if(fread(&numElements, sizeof(std::size_t), 1, fp) != 1) {
        delete[] elementCache;
        return nullptr;
      }
      if(swap) SwapBytes((char *)&numElements, sizeof(std::size_t), 1);
    }
    else {
      if(version >= 4.1) {
        if(fscanf(fp, "%d %d %d %zu", &entityDim, &entityTag, &elmType,
                  &numElements) != 4) {
          delete[] elementCache;
          return nullptr;
        }
      }
      else {
        if(fscanf(fp, "%d %d %d %zu", &entityTag, &entityDim, &elmType,
                  &numElements) != 4) {
          delete[] elementCache;
          return nullptr;
        }
      }
    }

    GEntity *entity = model->getEntityByTag(entityDim, entityTag);
    if(!entity) {
      Msg::Error("Unknown entity %d of dimension %d", entityTag, entityDim);
      delete[] elementCache;
      return nullptr;
    }
    if(entity->geomType() == GEntity::GhostCurve) {
      static_cast<ghostEdge *>(entity)->haveMesh(true);
    }
    else if(entity->geomType() == GEntity::GhostSurface) {
      static_cast<ghostFace *>(entity)->haveMesh(true);
    }
    else if(entity->geomType() == GEntity::GhostVolume) {
      static_cast<ghostRegion *>(entity)->haveMesh(true);
    }

    const int numVertPerElm = MElement::getInfoMSH(elmType);
    if(binary) {
      std::size_t n = 1 + numVertPerElm;
      std::vector<std::size_t> data(numElements * n);
      if(fread(&data[0], sizeof(std::size_t), numElements * n, fp) !=
         numElements * n) {
        delete[] elementCache;
        return nullptr;
      }
      if(swap)
        SwapBytes((char *)&data[0], sizeof(std::size_t), numElements * n);

      std::vector<MVertex *> vertices(numVertPerElm, (MVertex *)nullptr);
      for(std::size_t j = 0; j < numElements * n; j += n) {
        for(int k = 0; k < numVertPerElm; k++) {
          vertices[k] = model->getMeshVertexByTag(data[j + k + 1]);
          if(!vertices[k]) {
            Msg::Error("Unknown node %zu in element %zu", data[j + k + 1],
                       data[j]);
            delete[] elementCache;
            return nullptr;
          }
        }

        MElementFactory elementFactory;
        MElement *element = elementFactory.create(
          elmType, vertices, data[j], 0, false, 0, nullptr, nullptr, nullptr);
        if(!element) {
          Msg::Error("Could not create element %zu of type %d", data[j],
                     elmType);
          delete[] elementCache;
          return nullptr;
        }
        if(entity->geomType() != GEntity::GhostCurve &&
           entity->geomType() != GEntity::GhostSurface &&
           entity->geomType() != GEntity::GhostVolume) {
          entity->addElement(element);
        }

        minElementNum = std::min(minElementNum, data[j]);
        maxElementNum = std::max(maxElementNum, data[j]);

        elementCache[elementRead] =
          std::make_pair(data[j], std::make_pair(element, entityTag));
        elementRead++;

        if(totalNumElements > 100000)
          Msg::ProgressMeter(elementRead, true, "Reading elements");
      }
    }
    else {
      for(std::size_t j = 0; j < numElements; j++) {
        std::size_t elmTag = 0;
        if(fscanf(fp, "%zu", &elmTag) != 1) {
          delete[] elementCache;
          return nullptr;
        }

        // We read all node tags with a single fread() to improve
        // performance. Beware that this assumes that all node tags are on a
        // single line, which is not required by the MSH4 specification - we
        // might need to revert to multiple fscanf() calls instead (see
        // e.g. #2724)
        if(!fgets(str, sizeof(str), fp)) {
          delete[] elementCache;
          return nullptr;
        }

        std::vector<MVertex *> vertices(numVertPerElm, (MVertex *)nullptr);

        for(int k = 0; k < numVertPerElm; k++) {
          std::size_t vertexTag = 0;
          if(k != numVertPerElm - 1) {
            if(sscanf(str, "%zu %[0-9- ]", &vertexTag, str) != 2) {
              delete[] elementCache;
              return nullptr;
            }
          }
          else {
            if(sscanf(str, "%zu", &vertexTag) != 1) {
              delete[] elementCache;
              return nullptr;
            }
          }

          vertices[k] = model->getMeshVertexByTag(vertexTag);
          if(!vertices[k]) {
            Msg::Error("Unknown node %zu in element %zu", vertexTag, elmTag);
            delete[] elementCache;
            return nullptr;
          }
        }

        MElementFactory elementFactory;
        MElement *element = elementFactory.create(
          elmType, vertices, elmTag, 0, false, 0, nullptr, nullptr, nullptr);
        if(!element) {
          Msg::Error("Could not create element %zu of type %d", elmTag,
                     elmType);
          delete[] elementCache;
          return nullptr;
        }
        if(entity->geomType() != GEntity::GhostCurve &&
           entity->geomType() != GEntity::GhostSurface &&
           entity->geomType() != GEntity::GhostVolume) {
          entity->addElement(element);
        }

        minElementNum = std::min(minElementNum, elmTag);
        maxElementNum = std::max(maxElementNum, elmTag);

        elementCache[elementRead] =
          std::make_pair(elmTag, std::make_pair(element, entityTag));
        elementRead++;

        if(totalNumElements > 100000)
          Msg::ProgressMeter(elementRead, true, "Reading elements");
      }
    }
  }
  // if the vertex numbering is dense, we fill the vector cache, otherwise we
  // fill the map cache
  if(minElementNum == 1 && maxElementNum == totalNumElements) {
    Msg::Debug("Element numbering is dense");
    dense = true;
  }
  else if(maxElementNum < 10 * totalNumElements) {
    Msg::Debug(
      "Element numbering is fairly dense - still caching with a vector");
    dense = true;
  }
  else {
    Msg::Debug("Element numbering is not dense");
    dense = false;
  }

  return elementCache;
}

static bool readMSH4PeriodicNodes(GModel *const model, FILE *fp, bool binary,
                                  bool swap, double version)
{
  std::size_t numPeriodicLinks = 0;
  if(binary) {
    if(fread(&numPeriodicLinks, sizeof(std::size_t), 1, fp) != 1) {
      return false;
    }
    if(swap) SwapBytes((char *)&numPeriodicLinks, sizeof(std::size_t), 1);
  }
  else {
    if(fscanf(fp, "%zu", &numPeriodicLinks) != 1) { return false; }
  }

  for(std::size_t i = 0; i < numPeriodicLinks; i++) {
    int slaveDim = 0, slaveTag = 0, masterTag = 0;

    if(binary) {
      int data[3];
      if(fread(data, sizeof(int), 3, fp) != 3) { return false; }
      if(swap) SwapBytes((char *)data, sizeof(int), 3);
      slaveDim = data[0];
      slaveTag = data[1];
      masterTag = data[2];
    }
    else {
      if(fscanf(fp, "%d %d %d", &slaveDim, &slaveTag, &masterTag) != 3) {
        return false;
      }
    }

    GEntity *slave = nullptr, *master = nullptr;
    switch(slaveDim) {
    case 0:
      slave = model->getVertexByTag(slaveTag);
      master = model->getVertexByTag(masterTag);
      break;
    case 1:
      slave = model->getEdgeByTag(slaveTag);
      master = model->getEdgeByTag(masterTag);
      break;
    case 2:
      slave = model->getFaceByTag(slaveTag);
      master = model->getFaceByTag(masterTag);
      break;
    }

    if(!slave) {
      Msg::Info("Could not find periodic entity %d of dimension %d", slaveTag,
                slaveDim);
      continue;
    }
    if(!master) {
      Msg::Info("Could not find periodic source entity %d of dimension %d",
                masterTag, slaveDim);
      continue;
    }

    std::size_t correspondingVertexSize = 0;
    if(binary) {
      std::size_t numAffine;
      if(fread(&numAffine, sizeof(std::size_t), 1, fp) != 1) { return false; }
      if(swap) SwapBytes((char *)&numAffine, sizeof(std::size_t), 1);
      if(numAffine) {
        std::vector<double> tfo(numAffine);
        if(fread(&tfo[0], sizeof(double), numAffine, fp) != numAffine) {
          return false;
        }
        if(swap) SwapBytes((char *)&tfo[0], sizeof(double), numAffine);
        slave->setMeshMaster(master, tfo);
      }
      else {
        slave->setMeshMaster(master);
      }
      if(fread(&correspondingVertexSize, sizeof(std::size_t), 1, fp) != 1) {
        return false;
      }
      if(swap)
        SwapBytes((char *)&correspondingVertexSize, sizeof(std::size_t), 1);
    }
    else {
      if(version >= 4.1) {
        std::size_t numAffine = 0;
        if(fscanf(fp, "%zu", &numAffine) != 1) { return false; }
        if(numAffine) {
          std::vector<double> tfo(numAffine);
          for(std::size_t i = 0; i < numAffine; i++) {
            if(fscanf(fp, "%lf", &tfo[i]) != 1) { return false; }
          }
          slave->setMeshMaster(master, tfo);
        }
        else {
          slave->setMeshMaster(master);
        }
        if(fscanf(fp, "%zu", &correspondingVertexSize) != 1) { return false; }
      }
      else {
        char affine[256];
        if(fscanf(fp, "%s", affine) != 1) { return false; }
        if(!strncmp(affine, "Affine", 6)) {
          if(!fgets(affine, sizeof(affine), fp)) { return false; }
          std::vector<double> tfo(16);
          if(sscanf(affine,
                    "%lf %lf %lf %lf %lf %lf %lf %lf %lf %lf %lf %lf "
                    "%lf %lf %lf %lf",
                    &tfo[0], &tfo[1], &tfo[2], &tfo[3], &tfo[4], &tfo[5],
                    &tfo[6], &tfo[7], &tfo[8], &tfo[9], &tfo[10], &tfo[11],
                    &tfo[12], &tfo[13], &tfo[14], &tfo[15]) != 16) {
            return false;
          }
          slave->setMeshMaster(master, tfo);
          if(fscanf(fp, "%zu", &correspondingVertexSize) != 1) { return false; }
        }
        else {
          slave->setMeshMaster(master);
          if(sscanf(affine, "%zu", &correspondingVertexSize) != 1) {
            return false;
          }
        }
      }
    }

    for(std::size_t j = 0; j < correspondingVertexSize; j++) {
      std::size_t v1 = 0, v2 = 0;
      if(binary) {
        std::size_t data[2];
        if(fread(data, sizeof(std::size_t), 2, fp) != 2) { return false; }
        if(swap) SwapBytes((char *)data, sizeof(std::size_t), 2);
        v1 = data[0];
        v2 = data[1];
      }
      else {
        if(fscanf(fp, "%zu %zu", &v1, &v2) != 2) { return false; }
      }
      MVertex *mv1 = model->getMeshVertexByTag(v1);
      MVertex *mv2 = model->getMeshVertexByTag(v2);

      if(mv1 && mv2) { slave->correspondingVertices[mv1] = mv2; }
      else {
        if(!mv1) { Msg::Info("Could not find periodic node %d", v1); }
        else if(!mv2) {
          Msg::Info("Could not find periodic node %d", v2);
        }
      }
    }
  }
  return true;
}

static bool readMSH4GhostElements(GModel *const model, FILE *fp, bool binary,
                                  bool swap)
{
  std::size_t numGhostCells = 0;
  if(binary) {
    if(fread(&numGhostCells, sizeof(std::size_t), 1, fp) != 1) { return false; }
    if(swap) SwapBytes((char *)&numGhostCells, sizeof(std::size_t), 1);
  }
  else {
    if(fscanf(fp, "%zu", &numGhostCells) != 1) { return false; }
  }

  std::multimap<std::pair<MElement *, int>, int> ghostCells;
  for(std::size_t i = 0; i < numGhostCells; i++) {
    std::size_t elmTag = 0;
    int partNum = 0;
    std::size_t numGhostPartitions = 0;

    if(binary) {
      if(fread(&elmTag, sizeof(std::size_t), 1, fp) != 1) { return false; }
      if(swap) SwapBytes((char *)&elmTag, sizeof(std::size_t), 1);
      if(fread(&partNum, sizeof(int), 1, fp) != 1) { return false; }
      if(swap) SwapBytes((char *)&partNum, sizeof(int), 1);
      if(fread(&numGhostPartitions, sizeof(std::size_t), 1, fp) != 1) {
        return false;
      }
      if(swap) SwapBytes((char *)&numGhostPartitions, sizeof(std::size_t), 1);
    }
    else {
      if(fscanf(fp, "%zu %d %zu", &elmTag, &partNum, &numGhostPartitions) !=
         3) {
        return false;
      }
    }

    MElement *elm = model->getMeshElementByTag(elmTag);
    if(!elm) {
      Msg::Error("No element with tag %zu", elmTag);
      continue;
    }

    for(std::size_t j = 0; j < numGhostPartitions; j++) {
      int ghostPartition = 0;

      if(binary) {
        if(fread(&ghostPartition, sizeof(int), 1, fp) != 1) { return false; }
        if(swap) SwapBytes((char *)&ghostPartition, sizeof(int), 1);
      }
      else {
        if(fscanf(fp, "%d", &ghostPartition) != 1) { return false; }
      }

      ghostCells.insert(std::make_pair(std::make_pair(elm, partNum),
                                       ghostPartition));
    }
  }

  std::vector<GEntity *> ghostEntities(model->getNumPartitions() + 1, nullptr);
  std::vector<GEntity *> entities;
  model->getEntities(entities);
  for(std::size_t i = 0; i < entities.size(); i++) {
    GEntity *ge = entities[i];
    int partNum = -1;
    if(ge->geomType() == GEntity::GhostCurve)
      partNum = static_cast<ghostEdge *>(ge)->getPartition();
    else if(ge->geomType() == GEntity::GhostSurface)
      partNum = static_cast<ghostFace *>(ge)->getPartition();
    else if(ge->geomType() == GEntity::GhostVolume)
      partNum = static_cast<ghostRegion *>(ge)->getPartition();
    if(partNum >= 0 && partNum < (int)ghostEntities.size())
      ghostEntities[partNum] = ge;
  }

  for(auto it = ghostCells.begin(); it != ghostCells.end(); ++it) {
    if(it->second >= (int)ghostEntities.size()) {
      Msg::Error("Invalid partition %d in ghost elements", it->second);
      return false;
    }
    GEntity *ge = ghostEntities[it->second];
    if(!ge) {
      Msg::Warning("Missing ghost entity on partition %d", it->second);
    }
    else if(ge->geomType() == GEntity::GhostCurve) {
      static_cast<ghostEdge *>(ge)->addElement(it->first.first, it->first.second);
    }
    else if(ge->geomType() == GEntity::GhostSurface) {
      static_cast<ghostFace *>(ge)->addElement(it->first.first, it->first.second);
    }
    else if(ge->geomType() == GEntity::GhostVolume) {
      static_cast<ghostRegion *>(ge)->addElement(it->first.first, it->first.second);
    }
  }
  return true;
}

static bool readMSH4Parametrizations(GModel *const model, FILE *fp, bool binary)
{
  if(CTX::instance()->mesh.ignoreParametrizationMsh4) return true;

  std::size_t nParamE, nParamF;

  if(binary) {
    if(fread(&nParamE, sizeof(std::size_t), 1, fp) != 1) { return false; }
    if(fread(&nParamF, sizeof(std::size_t), 1, fp) != 1) { return false; }
  }
  else {
    if(fscanf(fp, "%zu %zu", &nParamE, &nParamF) != 2) { return false; }
  }

  // only report surface parametrizations
  Msg::Info("%zu parametrization%s", nParamF, nParamF > 1 ? "s" : "");
  Msg::StartProgressMeter(nParamF);

  for(std::size_t edge = 0; edge < nParamE; edge++) {
    int tag;
    if(binary) {
      if(fread(&tag, sizeof(int), 1, fp) != 1) { return false; }
    }
    else {
      if(fscanf(fp, "%d", &tag) != 1) { return false; }
    }
    GEdge *ge = model->getEdgeByTag(tag);
    if(ge) {
      discreteEdge *de = dynamic_cast<discreteEdge *>(ge);
      if(de) {
        if(!de->readParametrization(fp, binary)) return false;
      }
    }
  }

  for(std::size_t face = 0; face < nParamF; face++) {
    int tag;
    if(binary) {
      if(fread(&tag, sizeof(int), 1, fp) != 1) { return false; }
    }
    else {
      if(fscanf(fp, "%d", &tag) != 1) { return false; }
    }
    GFace *gf = model->getFaceByTag(tag);
    if(gf) {
      discreteFace *df = dynamic_cast<discreteFace *>(gf);
      if(df) {
        if(!df->readParametrization(fp, binary)) return false;
      }
    }
    Msg::ProgressMeter(face, true, "Processing parametrizations");
  }

  Msg::StopProgressMeter();

  return true;
}

int GModel::_readMSH4(const std::string &name)
{
  bool partitioned = false;
  FILE *fp = Fopen(name.c_str(), "rb");
  if(!fp) {
    Msg::Error("Unable to open file '%s'", name.c_str());
    return 0;
  }

  char str[1024] = "x";
  double version = 1.0;
  bool binary = false, swap = false;

  while(1) {
    while(str[0] != '$') {
      if(!fgets(str, sizeof(str), fp) || feof(fp)) break;
    }

    if(feof(fp)) break;

    std::string sectionName(&str[1]);
    std::string endSectionName = "End" + sectionName;

    if(!strncmp(&str[1], "MeshFormat", 10)) {
      if(!fgets(str, sizeof(str), fp) || feof(fp)) {
        fclose(fp);
        return 0;
      }

      int format;
      std::size_t size;
      if(sscanf(str, "%lf %d %zu", &version, &format, &size) != 3) {
        fclose(fp);
        return 0;
      }
      if(format) {
        binary = true;
        Msg::Debug("Mesh is in binary format");
        int one;
        if(fread(&one, sizeof(int), 1, fp) != 1) {
          fclose(fp);
          return 0;
        }
        if(one != 1) {
          swap = true;
          Msg::Debug("Swapping bytes from binary file");
        }
      }

      if(binary && size != sizeof(std::size_t)) {
        Msg::Error("Binary file has sizeof(size_t) = %d, not matching "
                   "machine sizeof(size_t) = %d",
                   size, sizeof(std::size_t));
        return false;
      }
      if(binary && version < 4.1) {
        Msg::Error("Can only read MSH 4.0 format in ASCII mode");
        return false;
      }
    }
    else if(!strncmp(&str[1], "PhysicalNames", 13)) {
      if(!fgets(str, sizeof(str), fp) || feof(fp)) {
        fclose(fp);
        return 0;
      }
      int numPhysicalNames = 0;
      if(sscanf(str, "%d", &numPhysicalNames) != 1) {
        fclose(fp);
        return 0;
      }
      std::vector<GModel::piter> iterators;
      getInnerPhysicalNamesIterators(iterators);
      for(int i = 0; i < numPhysicalNames; i++) {
        int dim = 0, tag = 0;
        if(fscanf(fp, "%d %d", &dim, &tag) != 2) {
          fclose(fp);
          return 0;
        }
        char name[256];
        if(!fgets(name, sizeof(name), fp)) {
          fclose(fp);
          return 0;
        }
        std::string physicalName = ExtractDoubleQuotedString(name, 256);
        if(physicalName.size())
          iterators[dim] =
            setPhysicalName(iterators[dim], physicalName, dim, tag);
      }
    }
    else if(!strncmp(&str[1], "Entities", 8)) {
      if(!readMSH4Entities(this, fp, false, binary, swap, version)) {
        Msg::Error("Could not read entities");
        fclose(fp);
        return 0;
      }
    }
    else if(!strncmp(&str[1], "PartitionedEntities", 19)) {
      if(!readMSH4Entities(this, fp, true, binary, swap, version)) {
        Msg::Error("Could not read partitioned entities");
        fclose(fp);
        return 0;
      }
      partitioned = true;
    }
    else if(!strncmp(&str[1], "Nodes", 5)) {
      _vertexVectorCache.clear();
      _vertexMapCache.clear();
      bool dense = false;
      std::size_t totalNumNodes = 0, maxNodeNum;
      std::pair<std::size_t, MVertex *> *vertexCache = readMSH4Nodes(
        this, fp, binary, dense, totalNumNodes, maxNodeNum, swap, version);
      Msg::StopProgressMeter();
      if(!vertexCache) {
        Msg::Error("Could not read nodes");
        fclose(fp);
        return false;
      }
      if(dense) {
        _vertexVectorCache.resize(maxNodeNum + 1, nullptr);
        for(std::size_t i = 0; i < totalNumNodes; i++) {
          if(!_vertexVectorCache[vertexCache[i].first]) {
            _vertexVectorCache[vertexCache[i].first] = vertexCache[i].second;
          }
          else {
            Msg::Info("Skipping duplicate node %d", vertexCache[i].first);
          }
        }
      }
      else {
        for(std::size_t i = 0; i < totalNumNodes; i++) {
          if(_vertexMapCache.count(vertexCache[i].first) == 0) {
            _vertexMapCache[vertexCache[i].first] = vertexCache[i].second;
          }
          else {
            Msg::Info("Skipping duplicate node %d", vertexCache[i].first);
          }
        }
      }
      delete[] vertexCache;
    }
    else if(!strncmp(&str[1], "Elements", 8)) {
      bool dense = false;
      std::size_t totalNumElements = 0, maxElementNum = 0;
      std::pair<std::size_t, std::pair<MElement *, int> > *elementCache =
        readMSH4Elements(this, fp, binary, dense, totalNumElements,
                         maxElementNum, swap, version);
      Msg::StopProgressMeter();
      if(!elementCache) {
        Msg::Error("Could not read elements");
        fclose(fp);
        return 0;
      }
      if(dense) {
        _elementVectorCache.resize(maxElementNum + 1, std::make_pair(nullptr, 0));
        for(std::size_t i = 0; i < totalNumElements; i++) {
          if(!_elementVectorCache[elementCache[i].first].first) {
            _elementVectorCache[elementCache[i].first] = elementCache[i].second;
          }
          else {
            Msg::Info("Skipping duplicate element %d", elementCache[i].first);
          }
        }
      }
      else {
        for(std::size_t i = 0; i < totalNumElements; i++) {
          if(_elementMapCache.count(elementCache[i].first) == 0) {
            _elementMapCache[elementCache[i].first] = elementCache[i].second;
          }
          else {
            Msg::Info("Skipping duplicate element %d", elementCache[i].first);
          }
        }
      }
      delete[] elementCache;
    }
    else if(!strncmp(&str[1], "Periodic", 8)) {
      if(!readMSH4PeriodicNodes(this, fp, binary, swap, version)) {
        Msg::Error("Could not read periodic section");
        fclose(fp);
        return 0;
      }
    }
    else if(!strncmp(&str[1], "GhostElements", 13)) {
      if(!readMSH4GhostElements(this, fp, binary, swap)) {
        Msg::Error("Could not read ghost elements");
        fclose(fp);
        return 0;
      }
    }
    else if(!strncmp(&str[1], "Parametrizations", 16)) {
      if(!readMSH4Parametrizations(this, fp, binary)) {
        Msg::Error("Could not read parametrizations");
        fclose(fp);
        return 0;
      }
    }
#if defined(HAVE_POST)
    else if(!strncmp(&str[1], "InterpolationScheme", 19)) {
      if(!PView::readMSHInterpolationScheme(fp)) {
        fclose(fp);
        return 0;
      }
    }
    else if(!strncmp(&str[1], "NodeData", 8) ||
            !strncmp(&str[1], "ElementData", 11) ||
            !strncmp(&str[1], "ElementNodeData", 15)) {
      if(!PView::readMSHViewData(name, fp, binary, swap, &str[1])) {
        fclose(fp);
        return 0;
      }
    }
#endif
    else if(strlen(&str[1]) > 0){
      if(!CTX::instance()->mesh.ignoreUnknownSections) {
        sectionName.pop_back();
        Msg::Info("Storing section $%s as model attribute", sectionName.c_str());
        std::vector<std::string> section;
        while(1) {
          if(!fgets(str, sizeof(str), fp) || feof(fp) ||
             !strncmp(&str[1], endSectionName.c_str(), endSectionName.size())) {
            break;
          }
          std::string s(str);
          if(s.back() == '\n') s.pop_back();
          if(s.back() == '\r') s.pop_back();
          section.push_back(s);
        }
        _attributes[sectionName] = section;
      }
    }

    while(strncmp(&str[1], endSectionName.c_str(), endSectionName.size())) {
      if(!fgets(str, sizeof(str), fp) || feof(fp)) { break; }
    }
    str[0] = 'a';
  }

  fclose(fp);

  if(partitioned) {
    // This part is added to ensure the compatibility between the new
    // partitioning and the old one.
    std::vector<GEntity *> entities;
    getEntities(entities);
    for(std::size_t i = 0; i < entities.size(); i++) {
      if(entities[i]->geomType() == GEntity::PartitionPoint) {
        partitionVertex *pv = static_cast<partitionVertex *>(entities[i]);
        if(pv->numPartitions() == 1) {
          const int part = pv->getPartition(0);
          for(std::size_t j = 0; j < pv->getNumMeshElements(); j++) {
            pv->getMeshElement(j)->setPartition(part);
          }
        }
      }
      else if(entities[i]->geomType() == GEntity::PartitionCurve) {
        partitionEdge *pe = static_cast<partitionEdge *>(entities[i]);
        if(pe->numPartitions() == 1) {
          const int part = pe->getPartition(0);
          for(std::size_t j = 0; j < pe->getNumMeshElements(); j++) {
            pe->getMeshElement(j)->setPartition(part);
          }
        }
      }
      else if(entities[i]->geomType() == GEntity::PartitionSurface) {
        partitionFace *pf = static_cast<partitionFace *>(entities[i]);
        if(pf->numPartitions() == 1) {
          const int part = pf->getPartition(0);
          for(std::size_t j = 0; j < pf->getNumMeshElements(); j++) {
            pf->getMeshElement(j)->setPartition(part);
          }
        }
      }
      else if(entities[i]->geomType() == GEntity::PartitionVolume) {
        partitionRegion *pr = static_cast<partitionRegion *>(entities[i]);
        if(pr->numPartitions() == 1) {
          const int part = pr->getPartition(0);
          for(std::size_t j = 0; j < pr->getNumMeshElements(); j++) {
            pr->getMeshElement(j)->setPartition(part);
          }
        }
      }
    }
  }

  return 1;
}

static void writeMSH4Physicals(FILE *fp, GEntity *const entity, bool binary)
{
  if(binary) {
    std::vector<int> phys = entity->getPhysicalEntities();
    std::size_t phySize = phys.size();
    fwrite(&phySize, sizeof(std::size_t), 1, fp);
    for(std::size_t i = 0; i < phys.size(); i++) {
      int phy = phys[i];
      fwrite(&phy, sizeof(int), 1, fp);
    }
  }
  else {
    std::vector<int> phys = entity->getPhysicalEntities();
    fprintf(fp, "%zu", phys.size());
    for(std::size_t i = 0; i < phys.size(); i++) {
      fprintf(fp, " %d", phys[i]);
    }
    fprintf(fp, " ");
  }
}

static void writeMSH4BoundingBox(SBoundingBox3d boundBox, FILE *fp,
                                 double scalingFactor, bool binary, int dim,
                                 double version)
{
  double bb[6] = {0., 0., 0., 0., 0., 0.};
  if(!boundBox.empty()) {
    boundBox *= scalingFactor;
    bb[0] = boundBox.min().x();
    bb[1] = boundBox.min().y();
    bb[2] = boundBox.min().z();
    bb[3] = boundBox.max().x();
    bb[4] = boundBox.max().y();
    bb[5] = boundBox.max().z();
  }
  if(binary) { fwrite(bb, sizeof(double), (dim > 0) ? 6 : 3, fp); }
  else {
    std::size_t n = (version < 4.1 || dim > 0) ? 6 : 3;
    for(std::size_t i = 0; i < n; i++) fprintf(fp, "%.16g ", bb[i]);
  }
}

static void writeMSH4Entities(GModel *const model, FILE *fp, bool partition,
                              bool binary, double scalingFactor, double version,
                              std::map<GEntity*, SBoundingBox3d> *entityBounds)
{
  std::set<GEntity *, GEntityPtrFullLessThan> ghost;
  std::set<GRegion *, GEntityPtrLessThan> regions;
  std::set<GFace *, GEntityPtrLessThan> faces;
  std::set<GEdge *, GEntityPtrLessThan> edges;
  std::set<GVertex *, GEntityPtrLessThan> vertices;

  if(partition) {
    for(auto it = model->firstVertex(); it != model->lastVertex(); ++it) {
      if(CTX::instance()->mesh.saveWithoutOrphans && (*it)->isOrphan())
        continue;
      if((*it)->geomType() == GEntity::PartitionPoint) vertices.insert(*it);
    }
    for(auto it = model->firstEdge(); it != model->lastEdge(); ++it) {
      if(CTX::instance()->mesh.saveWithoutOrphans && (*it)->isOrphan())
        continue;
      if((*it)->geomType() == GEntity::PartitionCurve) edges.insert(*it);
      if((*it)->geomType() == GEntity::GhostCurve) ghost.insert(*it);
    }
    for(auto it = model->firstFace(); it != model->lastFace(); ++it) {
      if(CTX::instance()->mesh.saveWithoutOrphans && (*it)->isOrphan())
        continue;
      if((*it)->geomType() == GEntity::PartitionSurface) faces.insert(*it);
      if((*it)->geomType() == GEntity::GhostSurface) ghost.insert(*it);
    }
    for(auto it = model->firstRegion(); it != model->lastRegion(); ++it) {
      if((*it)->geomType() == GEntity::PartitionVolume) regions.insert(*it);
      if((*it)->geomType() == GEntity::GhostVolume) ghost.insert(*it);
    }
  }
  else {
    for(auto it = model->firstVertex(); it != model->lastVertex(); ++it) {
      if(CTX::instance()->mesh.saveWithoutOrphans && (*it)->isOrphan())
        continue;
      if((*it)->geomType() != GEntity::PartitionPoint) vertices.insert(*it);
    }
    for(auto it = model->firstEdge(); it != model->lastEdge(); ++it) {
      if(CTX::instance()->mesh.saveWithoutOrphans && (*it)->isOrphan())
        continue;
      if((*it)->geomType() != GEntity::PartitionCurve &&
         (*it)->geomType() != GEntity::GhostCurve)
        edges.insert(*it);
    }
    for(auto it = model->firstFace(); it != model->lastFace(); ++it) {
      if(CTX::instance()->mesh.saveWithoutOrphans && (*it)->isOrphan())
        continue;
      if((*it)->geomType() != GEntity::PartitionSurface &&
         (*it)->geomType() != GEntity::GhostSurface)
        faces.insert(*it);
    }
    for(auto it = model->firstRegion(); it != model->lastRegion(); ++it) {
      if((*it)->geomType() != GEntity::PartitionVolume &&
         (*it)->geomType() != GEntity::GhostVolume)
        regions.insert(*it);
    }
  }

  if(partition)
    fprintf(fp, "$PartitionedEntities\n");
  else
    fprintf(fp, "$Entities\n");

  if(binary) {
    if(partition) {
      std::size_t numPartitions = model->getNumPartitions();
      fwrite(&numPartitions, sizeof(std::size_t), 1, fp);

      // write the ghostentities' tag
      std::size_t ghostSize = ghost.size();
      std::vector<int> tags;
      if(ghostSize) {
        tags.resize(2 * ghostSize);
        int index = 0;
        for(auto it = ghost.begin(); it != ghost.end(); ++it) {
          if((*it)->geomType() == GEntity::GhostCurve) {
            tags[index] = (*it)->tag();
            tags[++index] = static_cast<ghostEdge *>(*it)->getPartition();
          }
          else if((*it)->geomType() == GEntity::GhostSurface) {
            tags[index] = (*it)->tag();
            tags[++index] = static_cast<ghostFace *>(*it)->getPartition();
          }
          else if((*it)->geomType() == GEntity::GhostVolume) {
            tags[index] = (*it)->tag();
            tags[++index] = static_cast<ghostRegion *>(*it)->getPartition();
          }
          index++;
        }
      }
      fwrite(&ghostSize, sizeof(std::size_t), 1, fp);
      if(ghostSize) { fwrite(&tags[0], sizeof(int), 2 * ghostSize, fp); }
    }
    std::size_t verticesSize = vertices.size();
    std::size_t edgesSize = edges.size();
    std::size_t facesSize = faces.size();
    std::size_t regionsSize = regions.size();
    fwrite(&verticesSize, sizeof(std::size_t), 1, fp);
    fwrite(&edgesSize, sizeof(std::size_t), 1, fp);
    fwrite(&facesSize, sizeof(std::size_t), 1, fp);
    fwrite(&regionsSize, sizeof(std::size_t), 1, fp);

    for(auto it = vertices.begin(); it != vertices.end(); ++it) {
      int entityTag = (*it)->tag();
      fwrite(&entityTag, sizeof(int), 1, fp);
      if(partition) {
        partitionVertex *pv = static_cast<partitionVertex *>(*it);
        int parentEntityDim = 0, parentEntityTag = 0;
        if(pv->getParentEntity()) {
          parentEntityDim = pv->getParentEntity()->dim();
          parentEntityTag = pv->getParentEntity()->tag();
        }
        fwrite(&parentEntityDim, sizeof(int), 1, fp);
        fwrite(&parentEntityTag, sizeof(int), 1, fp);
        std::vector<int> partitions(pv->getPartitions().begin(),
                                    pv->getPartitions().end()); // FIXME
        std::size_t numPart = partitions.size();
        fwrite(&numPart, sizeof(std::size_t), 1, fp);
        fwrite(&partitions[0], sizeof(int), partitions.size(), fp);
      }
      SBoundingBox3d bb = entityBounds ? (*entityBounds)[*it] : (*it)->bounds();
      writeMSH4BoundingBox(bb, fp, scalingFactor, binary, 0, version);
      writeMSH4Physicals(fp, *it, binary);
    }

    int maxEdgeTag = 0;
    for(auto it = edges.begin(); it != edges.end(); ++it) {
      std::vector<GVertex *> vertices;
      std::vector<int> ori;

      maxEdgeTag = std::max(maxEdgeTag,(*it)->tag());

      if((*it)->getBeginVertex()) {
        vertices.push_back((*it)->getBeginVertex());
        ori.push_back(1);
      }
      if((*it)->getEndVertex()) { // convention that the end vertex is negative
        vertices.push_back((*it)->getEndVertex());
        ori.push_back(-1);
      }
      std::size_t verticesSize = vertices.size();
      int entityTag = (*it)->tag();
      fwrite(&entityTag, sizeof(int), 1, fp);
      if(partition) {
        partitionEdge *pe = static_cast<partitionEdge *>(*it);
        int parentEntityDim = 0, parentEntityTag = 0;
        if(pe->getParentEntity()) {
          parentEntityDim = pe->getParentEntity()->dim();
          parentEntityTag = pe->getParentEntity()->tag();
        }
        fwrite(&parentEntityDim, sizeof(int), 1, fp);
        fwrite(&parentEntityTag, sizeof(int), 1, fp);
        std::vector<int> partitions(pe->getPartitions().begin(),
                                    pe->getPartitions().end()); // FIXME
        std::size_t numPart = partitions.size();
        fwrite(&numPart, sizeof(std::size_t), 1, fp);
        fwrite(&partitions[0], sizeof(int), partitions.size(), fp);
      }
      SBoundingBox3d bb = entityBounds ? (*entityBounds)[*it] : (*it)->bounds();
      writeMSH4BoundingBox(bb, fp, scalingFactor, binary, 1, version);
      writeMSH4Physicals(fp, *it, binary);
      fwrite(&verticesSize, sizeof(std::size_t), 1, fp);
      int oriI = 0;
      for(auto itv = vertices.begin(); itv != vertices.end(); itv++) {
        int brepTag = ori[oriI] * (*itv)->tag();
        fwrite(&brepTag, sizeof(int), 1, fp);
        oriI++;
      }
    }

    for(auto it = faces.begin(); it != faces.end(); ++it) {
      std::vector<GEdge *> const &edges = (*it)->edges();
      // FIXME: temporary hack until we update the MSH4 format to handle
      // embedded entities - save embedded entities with fake tag > maxTag
      std::vector<GEdge *> const &embEdges = (*it)->embeddedEdges();

      std::vector<int> const &ori = (*it)->edgeOrientations();
      std::size_t edgesSize = edges.size();
      // FIXME: temporary hack until we update the MSH4 format to handle
      // embedded entities
      edgesSize += embEdges.size();

      int entityTag = (*it)->tag();
      fwrite(&entityTag, sizeof(int), 1, fp);
      if(partition) {
        partitionFace *pf = static_cast<partitionFace *>(*it);
        int parentEntityDim = 0, parentEntityTag = 0;
        if(pf->getParentEntity()) {
          parentEntityDim = pf->getParentEntity()->dim();
          parentEntityTag = pf->getParentEntity()->tag();
        }
        fwrite(&parentEntityDim, sizeof(int), 1, fp);
        fwrite(&parentEntityTag, sizeof(int), 1, fp);
        std::vector<int> partitions(pf->getPartitions().begin(),
                                    pf->getPartitions().end()); // FIXME
        std::size_t numPart = partitions.size();
        fwrite(&numPart, sizeof(std::size_t), 1, fp);
        fwrite(&partitions[0], sizeof(int), partitions.size(), fp);
      }
      SBoundingBox3d bb = entityBounds ? (*entityBounds)[*it] : (*it)->bounds();
      writeMSH4BoundingBox(bb, fp, scalingFactor, binary, 2, version);
      writeMSH4Physicals(fp, *it, binary);
      fwrite(&edgesSize, sizeof(std::size_t), 1, fp);
      std::vector<int> tags, signs;
      for(auto ite = edges.begin(); ite != edges.end(); ite++)
        tags.push_back((*ite)->tag());


      signs.insert(signs.end(), ori.begin(), ori.end());

      // FIXME: temporary hack until we update the MSH4 format to handle
      // embedded entities
      for(auto ite = embEdges.begin(); ite != embEdges.end(); ite++){
        tags.push_back((*ite)->tag() + maxEdgeTag);
        signs.push_back(1);
      }

      if(tags.size() == signs.size()) {
        for(std::size_t i = 0; i < tags.size(); i++)
          tags[i] *= (signs[i] > 0 ? 1 : -1);
      }
      for(std::size_t i = 0; i < tags.size(); i++) {
        int brepTag = tags[i];
        fwrite(&brepTag, sizeof(int), 1, fp);
      }
    }

    for(auto it = regions.begin(); it != regions.end(); ++it) {
      std::vector<GFace *> faces = (*it)->faces();
      std::vector<int> const &ori = (*it)->faceOrientations();
      std::size_t facesSize = faces.size();
      int entityTag = (*it)->tag();
      fwrite(&entityTag, sizeof(int), 1, fp);
      if(partition) {
        partitionRegion *pr = static_cast<partitionRegion *>(*it);
        int parentEntityDim = 0, parentEntityTag = 0;
        if(pr->getParentEntity()) {
          parentEntityDim = pr->getParentEntity()->dim();
          parentEntityTag = pr->getParentEntity()->tag();
        }
        fwrite(&parentEntityDim, sizeof(int), 1, fp);
        fwrite(&parentEntityTag, sizeof(int), 1, fp);
        std::vector<int> partitions(pr->getPartitions().begin(),
                                    pr->getPartitions().end()); // FIXME
        std::size_t numPart = partitions.size();
        fwrite(&numPart, sizeof(std::size_t), 1, fp);
        fwrite(&partitions[0], sizeof(int), partitions.size(), fp);
      }
      SBoundingBox3d bb = entityBounds ? (*entityBounds)[*it] : (*it)->bounds();
      writeMSH4BoundingBox(bb, fp, scalingFactor, binary, 3, version);
      writeMSH4Physicals(fp, *it, binary);
      fwrite(&facesSize, sizeof(std::size_t), 1, fp);
      std::vector<int> tags, signs;
      for(auto itf = faces.begin(); itf != faces.end(); itf++)
        tags.push_back((*itf)->tag());
      for(auto itf = ori.begin(); itf != ori.end(); itf++)
        signs.push_back(*itf);
      if(tags.size() == signs.size()) {
        for(std::size_t i = 0; i < tags.size(); i++)
          tags[i] *= (signs[i] > 0 ? 1 : -1);
      }
      for(std::size_t i = 0; i < tags.size(); i++) {
        int brepTag = tags[i];
        fwrite(&brepTag, sizeof(int), 1, fp);
      }
    }
    fprintf(fp, "\n");
  }
  else { // not binary --
    if(partition) {
      fprintf(fp, "%zu\n", model->getNumPartitions());

      // write the ghostentities' tag
      std::size_t ghostSize = ghost.size();
      std::vector<int> tags;
      if(ghostSize) {
        tags.resize(2 * ghostSize);
        int index = 0;
        for(auto it = ghost.begin(); it != ghost.end(); ++it) {
          if((*it)->geomType() == GEntity::GhostCurve) {
            tags[index] = (*it)->tag();
            tags[++index] = static_cast<ghostEdge *>(*it)->getPartition();
          }
          else if((*it)->geomType() == GEntity::GhostSurface) {
            tags[index] = (*it)->tag();
            tags[++index] = static_cast<ghostFace *>(*it)->getPartition();
          }
          else if((*it)->geomType() == GEntity::GhostVolume) {
            tags[index] = (*it)->tag();
            tags[++index] = static_cast<ghostRegion *>(*it)->getPartition();
          }
          index++;
        }
      }
      fprintf(fp, "%zu\n", ghostSize);
      if(ghostSize) {
        for(std::size_t i = 0; i < 2 * ghostSize; i += 2) {
          fprintf(fp, "%d %d\n", tags[i], tags[i + 1]);
        }
      }
    }
    fprintf(fp, "%zu %zu %zu %zu\n", vertices.size(), edges.size(),
            faces.size(), regions.size());

    for(auto it = vertices.begin(); it != vertices.end(); ++it) {
      fprintf(fp, "%d ", (*it)->tag());
      if(partition) {
        partitionVertex *pv = static_cast<partitionVertex *>(*it);
        int parentEntityDim = 0, parentEntityTag = 0;
        if(pv->getParentEntity()) {
          parentEntityDim = pv->getParentEntity()->dim();
          parentEntityTag = pv->getParentEntity()->tag();
        }
        fprintf(fp, "%d %d ", parentEntityDim, parentEntityTag);
        std::vector<int> partitions(pv->getPartitions().begin(),
                                    pv->getPartitions().end()); // FIXME
        fprintf(fp, "%zu ", partitions.size());
        for(std::size_t i = 0; i < partitions.size(); i++)
          fprintf(fp, "%d ", partitions[i]);
      }
      SBoundingBox3d bb = entityBounds ? (*entityBounds)[*it] : (*it)->bounds();
      writeMSH4BoundingBox(bb, fp, scalingFactor, binary, 0, version);
      writeMSH4Physicals(fp, *it, binary);
      fprintf(fp, "\n");
    }

    int maxEdgeTag = 0;
    for(auto it = edges.begin(); it != edges.end(); ++it) {
      maxEdgeTag = std::max(maxEdgeTag,(*it)->tag());
      std::vector<GVertex *> vertices;
      std::vector<int> ori;
      if((*it)->getBeginVertex()) {
        vertices.push_back((*it)->getBeginVertex());
        ori.push_back(1);
      }
      if((*it)->getEndVertex()) { // I use the convention that the end vertex is
                                  // negative
        vertices.push_back((*it)->getEndVertex());
        ori.push_back(-1);
      }
      fprintf(fp, "%d ", (*it)->tag());
      if(partition) {
        partitionEdge *pe = static_cast<partitionEdge *>(*it);
        int parentEntityDim = 0, parentEntityTag = 0;
        if(pe->getParentEntity()) {
          parentEntityDim = pe->getParentEntity()->dim();
          parentEntityTag = pe->getParentEntity()->tag();
        }
        fprintf(fp, "%d %d ", parentEntityDim, parentEntityTag);
        std::vector<int> partitions(pe->getPartitions().begin(),
                                    pe->getPartitions().end()); // FIXME
        fprintf(fp, "%zu ", partitions.size());
        for(std::size_t i = 0; i < partitions.size(); i++)
          fprintf(fp, "%d ", partitions[i]);
      }
      SBoundingBox3d bb = entityBounds ? (*entityBounds)[*it] : (*it)->bounds();
      writeMSH4BoundingBox(bb, fp, scalingFactor, binary, 1, version);
      writeMSH4Physicals(fp, *it, binary);
      fprintf(fp, "%zu ", vertices.size());
      int oriI = 0;
      for(auto itv = vertices.begin(); itv != vertices.end(); itv++) {
        fprintf(fp, "%d ", ori[oriI] * (*itv)->tag());
        oriI++;
      }
      fprintf(fp, "\n");
    }

    for(auto it = faces.begin(); it != faces.end(); ++it) {
      std::vector<GEdge *> const &edges = (*it)->edges();
      // FIXME: temporary hack until we update the MSH4 format to handle
      // embedded entities
      std::vector<GEdge *> const &embEdges = (*it)->embeddedEdges();

      std::vector<int> const &ori = (*it)->edgeOrientations();
      fprintf(fp, "%d ", (*it)->tag());
      if(partition) {
        partitionFace *pf = static_cast<partitionFace *>(*it);
        int parentEntityDim = 0, parentEntityTag = 0;
        if(pf->getParentEntity()) {
          parentEntityDim = pf->getParentEntity()->dim();
          parentEntityTag = pf->getParentEntity()->tag();
        }
        fprintf(fp, "%d %d ", parentEntityDim, parentEntityTag);
        std::vector<int> partitions(pf->getPartitions().begin(),
                                    pf->getPartitions().end()); // FIXME
        fprintf(fp, "%zu ", partitions.size());
        for(std::size_t i = 0; i < partitions.size(); i++)
          fprintf(fp, "%d ", partitions[i]);
      }
      SBoundingBox3d bb = entityBounds ? (*entityBounds)[*it] : (*it)->bounds();
      writeMSH4BoundingBox(bb, fp, scalingFactor, binary, 2, version);
      writeMSH4Physicals(fp, *it, binary);
      // FIXME: temporary hack until we update the MSH4 format to handle
      // embedded entities
      fprintf(fp, "%zu ", edges.size() + embEdges.size());
      std::vector<int> tags, signs;
      for(auto ite = edges.begin(); ite != edges.end(); ite++)
        tags.push_back((*ite)->tag());
      for(auto ite = ori.begin(); ite != ori.end(); ite++)
        signs.push_back(*ite);
      // FIXME: temporary hack until we update the MSH4 format to handle
      // embedded entities
      for(auto ite = embEdges.begin(); ite != embEdges.end(); ite++){
        tags.push_back((*ite)->tag() + maxEdgeTag);
        signs.push_back(1);
      }
      if(tags.size() == signs.size()) {
        for(std::size_t i = 0; i < tags.size(); i++)
          tags[i] *= (signs[i] > 0 ? 1 : -1);
      }
      for(std::size_t i = 0; i < tags.size(); i++) fprintf(fp, "%d ", tags[i]);
      fprintf(fp, "\n");
    }

    for(auto it = regions.begin(); it != regions.end(); ++it) {
      std::vector<GFace *> const &faces = (*it)->faces();
      std::vector<int> const &ori = (*it)->faceOrientations();
      fprintf(fp, "%d ", (*it)->tag());
      if(partition) {
        partitionRegion *pr = static_cast<partitionRegion *>(*it);
        int parentEntityDim = 0, parentEntityTag = 0;
        if(pr->getParentEntity()) {
          parentEntityDim = pr->getParentEntity()->dim();
          parentEntityTag = pr->getParentEntity()->tag();
        }
        fprintf(fp, "%d %d ", parentEntityDim, parentEntityTag);

        fprintf(fp, "%zu ", pr->getPartitions().size());

        for(auto const partition : pr->getPartitions()) {
          fprintf(fp, "%d ", partition);
        }
      }
      SBoundingBox3d bb = entityBounds ? (*entityBounds)[*it] : (*it)->bounds();
      writeMSH4BoundingBox(bb, fp, scalingFactor, binary, 3, version);
      writeMSH4Physicals(fp, *it, binary);
      fprintf(fp, "%zu ", faces.size());

      std::vector<int> tags(faces.size());
      std::transform(begin(faces), end(faces), begin(tags),
                     [](const GFace *const face) { return face->tag(); });

      std::vector<int> signs(ori.begin(), ori.end());

      if(tags.size() == signs.size()) {
        for(std::size_t i = 0; i < tags.size(); i++)
          tags[i] *= (signs[i] > 0 ? 1 : -1);
      }

      for(auto const tag : tags) { fprintf(fp, "%d ", tag); }
      fprintf(fp, "\n");
    }
  }

  if(partition)
    fprintf(fp, "$EndPartitionedEntities\n");
  else
    fprintf(fp, "$EndEntities\n");
}

static void writeMSH4EntityNodes(GEntity *ge, FILE *fp, bool binary,
                                 int saveParametric, double scalingFactor,
                                 double version)
{
  int parametric = saveParametric;
  if(ge->dim() != 1 && ge->dim() != 2)
    parametric = 0; // Gmsh only stores parametric coordinates for dim 1 and 2

  std::size_t numVerts = ge->getNumMeshVertices();

  if(binary) {
    int entityDim = ge->dim();
    int entityTag = ge->tag();
    fwrite(&entityDim, sizeof(int), 1, fp);
    fwrite(&entityTag, sizeof(int), 1, fp);
    fwrite(&parametric, sizeof(int), 1, fp);
    fwrite(&numVerts, sizeof(std::size_t), 1, fp);
  }
  else {
    fprintf(fp, "%d %d %d %zu\n", (version >= 4.1) ? ge->dim() : ge->tag(),
            (version >= 4.1) ? ge->tag() : ge->dim(), parametric,
            ge->getNumMeshVertices());
  }

  if(!numVerts) {
    return;
  }

  std::size_t n = 3;
  if(parametric) n += ge->dim();

  if(binary) {
    std::vector<size_t> tags(numVerts);
    for(std::size_t i = 0; i < numVerts; i++)
      tags[i] = ge->getMeshVertex(i)->getNum();
    fwrite(&tags[0], sizeof(std::size_t), numVerts, fp);
    std::vector<double> coord(n * numVerts);
    std::size_t j = 0;
    for(std::size_t i = 0; i < numVerts; i++) {
      MVertex *mv = ge->getMeshVertex(i);
      coord[j++] = mv->x() * scalingFactor;
      coord[j++] = mv->y() * scalingFactor;
      coord[j++] = mv->z() * scalingFactor;
      if(n >= 4) mv->getParameter(0, coord[j++]);
      if(n == 5) mv->getParameter(1, coord[j++]);
    }
    fwrite(&coord[0], sizeof(double), n * numVerts, fp);
  }
  else {
    if(version >= 4.1) {
      for(std::size_t i = 0; i < numVerts; i++)
        fprintf(fp, "%zu\n", ge->getMeshVertex(i)->getNum());
    }
    for(std::size_t i = 0; i < numVerts; i++) {
      MVertex *mv = ge->getMeshVertex(i);
      double x = mv->x() * scalingFactor;
      double y = mv->y() * scalingFactor;
      double z = mv->z() * scalingFactor;
      if(version < 4.1) fprintf(fp, "%zu ", mv->getNum());
      if(n == 5) {
        double u, v;
        mv->getParameter(0, u);
        mv->getParameter(1, v);
        fprintf(fp, "%.16g %.16g %.16g %.16g %.16g\n", x, y, z, u, v);
      }
      else if(n == 4) {
        double u;
        mv->getParameter(0, u);
        fprintf(fp, "%.16g %.16g %.16g %.16g\n", x, y, z, u);
      }
      else {
        fprintf(fp, "%.16g %.16g %.16g\n", x, y, z);
      }
    }
  }
}

static std::size_t
getAdditionalEntities(std::set<GRegion *, GEntityPtrLessThan> &regions,
                      std::set<GFace *, GEntityPtrLessThan> &faces,
                      std::set<GEdge *, GEntityPtrLessThan> &edges,
                      std::set<GVertex *, GEntityPtrLessThan> &vertices)
{
  std::size_t numVertices = 0;

  for(auto it = vertices.begin(); it != vertices.end(); ++it) {
    numVertices += (*it)->getNumMeshVertices();
  }

  for(auto it = edges.begin(); it != edges.end(); ++it) {
    numVertices += (*it)->getNumMeshVertices();
    for(std::size_t i = 0; i < (*it)->getNumMeshElements(); i++) {
      for(std::size_t j = 0; j < (*it)->getMeshElement(i)->getNumVertices();
          j++) {
        GEntity *entity = (*it)->getMeshElement(i)->getVertex(j)->onWhat();
        if(entity && entity != (*it)) {
          switch(entity->dim()) {
          case 0:
            if(vertices.find(static_cast<GVertex *>(entity)) ==
               vertices.end()) {
              vertices.insert(static_cast<GVertex *>(entity));
              numVertices += entity->getNumMeshVertices();
            }
            break;
          case 1:
            if(edges.find(static_cast<GEdge *>(entity)) == edges.end()) {
              edges.insert(static_cast<GEdge *>(entity));
              numVertices += entity->getNumMeshVertices();
            }
            break;
          case 2:
            if(faces.find(static_cast<GFace *>(entity)) == faces.end()) {
              faces.insert(static_cast<GFace *>(entity));
              numVertices += entity->getNumMeshVertices();
            }
            break;
          case 3:
            if(regions.find(static_cast<GRegion *>(entity)) == regions.end()) {
              regions.insert(static_cast<GRegion *>(entity));
              numVertices += entity->getNumMeshVertices();
            }
            break;
          default: break;
          }
        }
      }
    }
  }

  for(auto it = faces.begin(); it != faces.end(); ++it) {
    numVertices += (*it)->getNumMeshVertices();
    for(std::size_t i = 0; i < (*it)->getNumMeshElements(); i++) {
      for(std::size_t j = 0; j < (*it)->getMeshElement(i)->getNumVertices();
          j++) {
        GEntity *entity = (*it)->getMeshElement(i)->getVertex(j)->onWhat();
        if(entity && entity != (*it)) {
          switch(entity->dim()) {
          case 0:
            if(vertices.find(static_cast<GVertex *>(entity)) ==
               vertices.end()) {
              vertices.insert(static_cast<GVertex *>(entity));
              numVertices += entity->getNumMeshVertices();
            }
            break;
          case 1:
            if(edges.find(static_cast<GEdge *>(entity)) == edges.end()) {
              edges.insert(static_cast<GEdge *>(entity));
              numVertices += entity->getNumMeshVertices();
            }
            break;
          case 2:
            if(faces.find(static_cast<GFace *>(entity)) == faces.end()) {
              faces.insert(static_cast<GFace *>(entity));
              numVertices += entity->getNumMeshVertices();
            }
            break;
          case 3:
            if(regions.find(static_cast<GRegion *>(entity)) == regions.end()) {
              regions.insert(static_cast<GRegion *>(entity));
              numVertices += entity->getNumMeshVertices();
            }
            break;
          default: break;
          }
        }
      }
    }
  }

  for(auto it = regions.begin(); it != regions.end(); ++it) {
    numVertices += (*it)->getNumMeshVertices();
    for(std::size_t i = 0; i < (*it)->getNumMeshElements(); i++) {
      for(std::size_t j = 0; j < (*it)->getMeshElement(i)->getNumVertices();
          j++) {
        GEntity *entity = (*it)->getMeshElement(i)->getVertex(j)->onWhat();
        if(entity && entity != (*it)) {
          switch(entity->dim()) {
          case 0:
            if(vertices.find(static_cast<GVertex *>(entity)) ==
               vertices.end()) {
              vertices.insert(static_cast<GVertex *>(entity));
              numVertices += entity->getNumMeshVertices();
            }
            break;
          case 1:
            if(edges.find(static_cast<GEdge *>(entity)) == edges.end()) {
              edges.insert(static_cast<GEdge *>(entity));
              numVertices += entity->getNumMeshVertices();
            }
            break;
          case 2:
            if(faces.find(static_cast<GFace *>(entity)) == faces.end()) {
              faces.insert(static_cast<GFace *>(entity));
              numVertices += entity->getNumMeshVertices();
            }
            break;
          case 3:
            if(regions.find(static_cast<GRegion *>(entity)) == regions.end()) {
              regions.insert(static_cast<GRegion *>(entity));
              numVertices += entity->getNumMeshVertices();
            }
            break;
          default: break;
          }
        }
      }
    }
  }

  return numVertices;
}

static void
getEntitiesToSave(GModel *const model, bool partitioned,
                  int partitionToSave, bool saveAll,
                  std::set<GRegion *, GEntityPtrLessThan> &regions,
                  std::set<GFace *, GEntityPtrLessThan> &faces,
                  std::set<GEdge *, GEntityPtrLessThan> &edges,
                  std::set<GVertex *, GEntityPtrLessThan> &vertices)
{
  if(partitioned) {
    for(auto it = model->firstVertex(); it != model->lastVertex(); ++it) {
      if(CTX::instance()->mesh.saveWithoutOrphans && (*it)->isOrphan())
        continue;
      if((*it)->geomType() == GEntity::PartitionPoint) {
        partitionVertex *pv = static_cast<partitionVertex *>(*it);
        if(!partitionToSave ||
           std::find(pv->getPartitions().begin(), pv->getPartitions().end(),
                     partitionToSave) != pv->getPartitions().end())
          vertices.insert(pv);
      }
    }
    for(auto it = model->firstEdge(); it != model->lastEdge(); ++it) {
      if(CTX::instance()->mesh.saveWithoutOrphans && (*it)->isOrphan())
        continue;
      if((*it)->geomType() == GEntity::PartitionCurve) {
        partitionEdge *pe = static_cast<partitionEdge *>(*it);
        if(!partitionToSave ||
           std::find(pe->getPartitions().begin(), pe->getPartitions().end(),
                     partitionToSave) != pe->getPartitions().end())
          edges.insert(pe);
      }
      else if((*it)->geomType() == GEntity::GhostCurve) {
        ghostEdge *ge = static_cast<ghostEdge *>(*it);
        if(ge->getPartition() == partitionToSave)
          edges.insert(ge);
      }
    }
    for(auto it = model->firstFace(); it != model->lastFace(); ++it) {
      if(CTX::instance()->mesh.saveWithoutOrphans && (*it)->isOrphan())
        continue;
      if((*it)->geomType() == GEntity::PartitionSurface) {
        partitionFace *pf = static_cast<partitionFace *>(*it);
        if(!partitionToSave ||
           std::find(pf->getPartitions().begin(), pf->getPartitions().end(),
                     partitionToSave) != pf->getPartitions().end())
          faces.insert(pf);
      }
      else if((*it)->geomType() == GEntity::GhostSurface) {
        ghostFace *gf = static_cast<ghostFace *>(*it);
        if(gf->getPartition() == partitionToSave)
          faces.insert(gf);
      }
    }
    for(auto it = model->firstRegion(); it != model->lastRegion(); ++it) {
      if((*it)->geomType() == GEntity::PartitionVolume) {
        partitionRegion *pr = static_cast<partitionRegion *>(*it);
        if(!partitionToSave ||
           std::find(pr->getPartitions().begin(), pr->getPartitions().end(),
                     partitionToSave) != pr->getPartitions().end())
          regions.insert(pr);
      }
      else if((*it)->geomType() == GEntity::GhostVolume) {
        ghostRegion *gr = static_cast<ghostRegion *>(*it);
        if(gr->getPartition() == partitionToSave)
          regions.insert(gr);
      }
    }
  }
  else {
    for(auto it = model->firstVertex(); it != model->lastVertex(); ++it) {
      if(CTX::instance()->mesh.saveWithoutOrphans && (*it)->isOrphan())
        continue;
      if((*it)->geomType() != GEntity::PartitionPoint &&
         (saveAll || (!saveAll && (*it)->getPhysicalEntities().size() != 0)))
        vertices.insert(*it);
    }
    for(auto it = model->firstEdge(); it != model->lastEdge(); ++it) {
      if(CTX::instance()->mesh.saveWithoutOrphans && (*it)->isOrphan())
        continue;
      if((*it)->geomType() != GEntity::PartitionCurve &&
         (saveAll || (!saveAll && (*it)->getPhysicalEntities().size() != 0) ||
          (*it)->geomType() == GEntity::GhostCurve))
        edges.insert(*it);
    }
    for(auto it = model->firstFace(); it != model->lastFace(); ++it) {
      if(CTX::instance()->mesh.saveWithoutOrphans && (*it)->isOrphan())
        continue;
      if((*it)->geomType() != GEntity::PartitionSurface &&
         (saveAll || (!saveAll && (*it)->getPhysicalEntities().size() != 0) ||
          (*it)->geomType() == GEntity::GhostSurface))
        faces.insert(*it);
    }
    for(auto it = model->firstRegion(); it != model->lastRegion(); ++it) {
      if((*it)->geomType() != GEntity::PartitionVolume &&
         (saveAll || (!saveAll && (*it)->getPhysicalEntities().size() != 0) ||
          (*it)->geomType() == GEntity::GhostVolume))
        regions.insert(*it);
    }
  }
}

static void writeMSH4Nodes(GModel *const model, FILE *fp, bool partitioned,
                           int partitionToSave, bool binary, int saveParametric,
                           double scalingFactor, bool saveAll, double version)
{
  std::set<GRegion *, GEntityPtrLessThan> regions;
  std::set<GFace *, GEntityPtrLessThan> faces;
  std::set<GEdge *, GEntityPtrLessThan> edges;
  std::set<GVertex *, GEntityPtrLessThan> vertices;
  getEntitiesToSave(model, partitioned, partitionToSave, saveAll, regions,
                    faces, edges, vertices);

  std::size_t numNodes = (saveAll && !partitioned &&
                          !CTX::instance()->mesh.saveWithoutOrphans) ?
    model->getNumMeshVertices() :
    getAdditionalEntities(regions, faces, edges, vertices);

  if(!numNodes) return;

  fprintf(fp, "$Nodes\n");

  std::size_t minTag = std::numeric_limits<std::size_t>::max(), maxTag = 0;
  for(auto it = vertices.begin(); it != vertices.end(); ++it) {
    for(std::size_t i = 0; i < (*it)->getNumMeshVertices(); i++) {
      minTag = std::min(minTag, (*it)->getMeshVertex(i)->getNum());
      maxTag = std::max(maxTag, (*it)->getMeshVertex(i)->getNum());
    }
  }
  for(auto it = edges.begin(); it != edges.end(); ++it) {
    for(std::size_t i = 0; i < (*it)->getNumMeshVertices(); i++) {
      minTag = std::min(minTag, (*it)->getMeshVertex(i)->getNum());
      maxTag = std::max(maxTag, (*it)->getMeshVertex(i)->getNum());
    }
  }
  for(auto it = faces.begin(); it != faces.end(); ++it) {
    for(std::size_t i = 0; i < (*it)->getNumMeshVertices(); i++) {
      minTag = std::min(minTag, (*it)->getMeshVertex(i)->getNum());
      maxTag = std::max(maxTag, (*it)->getMeshVertex(i)->getNum());
    }
  }
  for(auto it = regions.begin(); it != regions.end(); ++it) {
    for(std::size_t i = 0; i < (*it)->getNumMeshVertices(); i++) {
      minTag = std::min(minTag, (*it)->getMeshVertex(i)->getNum());
      maxTag = std::max(maxTag, (*it)->getMeshVertex(i)->getNum());
    }
  }

  if(binary) {
    std::size_t numSection =
      vertices.size() + edges.size() + faces.size() + regions.size();
    fwrite(&numSection, sizeof(std::size_t), 1, fp);
    fwrite(&numNodes, sizeof(std::size_t), 1, fp);
    fwrite(&minTag, sizeof(std::size_t), 1, fp);
    fwrite(&maxTag, sizeof(std::size_t), 1, fp);
  }
  else {
    if(version >= 4.1) {
      fprintf(fp, "%zu %zu %zu %zu\n",
              vertices.size() + edges.size() + faces.size() + regions.size(),
              numNodes, minTag, maxTag);
    }
    else {
      fprintf(fp, "%zu %zu\n",
              vertices.size() + edges.size() + faces.size() + regions.size(),
              numNodes);
    }
  }

  for(auto it = vertices.begin(); it != vertices.end(); ++it) {
    writeMSH4EntityNodes(*it, fp, binary, saveParametric, scalingFactor,
                         version);
  }
  for(auto it = edges.begin(); it != edges.end(); ++it) {
    writeMSH4EntityNodes(*it, fp, binary, saveParametric, scalingFactor,
                         version);
  }
  for(auto it = faces.begin(); it != faces.end(); ++it) {
    writeMSH4EntityNodes(*it, fp, binary, saveParametric, scalingFactor,
                         version);
  }
  for(auto it = regions.begin(); it != regions.end(); ++it) {
    writeMSH4EntityNodes(*it, fp, binary, saveParametric, scalingFactor,
                         version);
  }

  if(binary) fprintf(fp, "\n");

  fprintf(fp, "$EndNodes\n");
}

static void writeMSH4Elements(GModel *const model, FILE *fp, bool partitioned,
                              int partitionToSave, bool binary, bool saveAll,
                              double version)
{
  std::set<GRegion *, GEntityPtrLessThan> regions;
  std::set<GFace *, GEntityPtrLessThan> faces;
  std::set<GEdge *, GEntityPtrLessThan> edges;
  std::set<GVertex *, GEntityPtrLessThan> vertices;
  getEntitiesToSave(model, partitioned, partitionToSave, saveAll, regions,
                    faces, edges, vertices);

  std::map<std::pair<int, int>, std::vector<MElement *> > elementsByType[4];
  std::size_t numElements = 0;

  for(auto it = vertices.begin(); it != vertices.end(); ++it) {
    if(!saveAll && (*it)->physicals.size() == 0) continue;

    numElements += (*it)->points.size();
    for(std::size_t i = 0; i < (*it)->points.size(); i++) {
      std::pair<int, int> p((*it)->tag(), (*it)->points[i]->getTypeForMSH());
      elementsByType[0][p].push_back((*it)->points[i]);
    }
  }

  for(auto it = edges.begin(); it != edges.end(); ++it) {
    if(!saveAll && (*it)->physicals.size() == 0 &&
       (*it)->geomType() != GEntity::GhostCurve)
      continue;

    numElements += (*it)->lines.size();
    for(std::size_t i = 0; i < (*it)->lines.size(); i++) {
      std::pair<int, int> p((*it)->tag(), (*it)->lines[i]->getTypeForMSH());
      elementsByType[1][p].push_back((*it)->lines[i]);
    }
  }

  for(auto it = faces.begin(); it != faces.end(); ++it) {
    if(!saveAll && (*it)->physicals.size() == 0 &&
       (*it)->geomType() != GEntity::GhostSurface)
      continue;

    numElements += (*it)->triangles.size();
    for(std::size_t i = 0; i < (*it)->triangles.size(); i++) {
      std::pair<int, int> p((*it)->tag(), (*it)->triangles[i]->getTypeForMSH());
      elementsByType[2][p].push_back((*it)->triangles[i]);
    }
    numElements += (*it)->quadrangles.size();
    for(std::size_t i = 0; i < (*it)->quadrangles.size(); i++) {
      std::pair<int, int> p((*it)->tag(),
                            (*it)->quadrangles[i]->getTypeForMSH());
      elementsByType[2][p].push_back((*it)->quadrangles[i]);
    }
  }

  for(auto it = regions.begin(); it != regions.end(); ++it) {
    if(!saveAll && (*it)->physicals.size() == 0 &&
       (*it)->geomType() != GEntity::GhostVolume)
      continue;

    numElements += (*it)->tetrahedra.size();
    for(std::size_t i = 0; i < (*it)->tetrahedra.size(); i++) {
      std::pair<int, int> p((*it)->tag(),
                            (*it)->tetrahedra[i]->getTypeForMSH());
      elementsByType[3][p].push_back((*it)->tetrahedra[i]);
    }
    numElements += (*it)->hexahedra.size();
    for(std::size_t i = 0; i < (*it)->hexahedra.size(); i++) {
      std::pair<int, int> p((*it)->tag(), (*it)->hexahedra[i]->getTypeForMSH());
      elementsByType[3][p].push_back((*it)->hexahedra[i]);
    }
    numElements += (*it)->prisms.size();
    for(std::size_t i = 0; i < (*it)->prisms.size(); i++) {
      std::pair<int, int> p((*it)->tag(), (*it)->prisms[i]->getTypeForMSH());
      elementsByType[3][p].push_back((*it)->prisms[i]);
    }
    numElements += (*it)->pyramids.size();
    for(std::size_t i = 0; i < (*it)->pyramids.size(); i++) {
      std::pair<int, int> p((*it)->tag(), (*it)->pyramids[i]->getTypeForMSH());
      elementsByType[3][p].push_back((*it)->pyramids[i]);
    }
    numElements += (*it)->trihedra.size();
    for(std::size_t i = 0; i < (*it)->trihedra.size(); i++) {
      std::pair<int, int> p((*it)->tag(), (*it)->trihedra[i]->getTypeForMSH());
      elementsByType[3][p].push_back((*it)->trihedra[i]);
    }
  }

  if(!numElements) return;

  fprintf(fp, "$Elements\n");

  std::size_t numSection = 0;
  for(int dim = 0; dim <= 3; dim++) numSection += elementsByType[dim].size();

  std::size_t minTag = std::numeric_limits<std::size_t>::max(), maxTag = 0;
  for(int dim = 0; dim <= 3; dim++) {
    for(auto it = elementsByType[dim].begin(); it != elementsByType[dim].end();
        ++it) {
      for(std::size_t i = 0; i < it->second.size(); i++) {
        minTag = std::min(minTag, it->second[i]->getNum());
        maxTag = std::max(maxTag, it->second[i]->getNum());
      }
    }
  }

  if(binary) {
    fwrite(&numSection, sizeof(std::size_t), 1, fp);
    fwrite(&numElements, sizeof(std::size_t), 1, fp);
    fwrite(&minTag, sizeof(std::size_t), 1, fp);
    fwrite(&maxTag, sizeof(std::size_t), 1, fp);
  }
  else {
    if(version >= 4.1)
      fprintf(fp, "%zu %zu %zu %zu\n", numSection, numElements, minTag, maxTag);
    else
      fprintf(fp, "%zu %zu\n", numSection, numElements);
  }

  for(int dim = 0; dim <= 3; dim++) {
    for(auto it = elementsByType[dim].begin(); it != elementsByType[dim].end();
        ++it) {
      int entityTag = it->first.first;
      int elmType = it->first.second;
      std::size_t numElm = it->second.size();
      if(binary) {
        fwrite(&dim, sizeof(int), 1, fp);
        fwrite(&entityTag, sizeof(int), 1, fp);
        fwrite(&elmType, sizeof(int), 1, fp);
        fwrite(&numElm, sizeof(std::size_t), 1, fp);
      }
      else {
        fprintf(fp, "%d %d %d %zu\n", (version >= 4.1) ? dim : entityTag,
                (version >= 4.1) ? entityTag : dim, elmType, numElm);
      }

      std::size_t N = it->second.size();
      if(binary) {
        const int numVertPerElm = MElement::getInfoMSH(elmType);
        std::size_t n = 1 + numVertPerElm;
        std::vector<std::size_t> tags(N * n);
        std::size_t k = 0;
        for(std::size_t i = 0; i < N; i++) {
          MElement *e = it->second[i];
          tags[k] = e->getNum();
          for(int j = 0; j < numVertPerElm; j++) {
            tags[k + 1 + j] = e->getVertex(j)->getNum();
          }
          k += n;
        }
        fwrite(&tags[0], sizeof(std::size_t), N * n, fp);
      }
      else {
        for(std::size_t i = 0; i < N; i++) {
          MElement *e = it->second[i];
          fprintf(fp, "%zu ", e->getNum());
          for(std::size_t i = 0; i < e->getNumVertices(); i++) {
            fprintf(fp, "%zu ", e->getVertex(i)->getNum());
          }
          fprintf(fp, "\n");
        }
      }
    }
  }

  if(binary) fprintf(fp, "\n");

  fprintf(fp, "$EndElements\n");
}

static void writeMSH4PeriodicNodes(GModel *const model, FILE *fp,
                                   bool binary, double version)
{
  // To avoid saving correspondences bwteen nodes that are not saved (either in
  // the same file or not at all, e.g. in the partitioned case, or simply if
  // some physical entities are not defined), we could only apply the code below
  // to the entities returned by getEntitiesForNodes().

  // The current choice is to save everything, and not complain if a node is not
  // found when reading the file. This should be reevaluated at some point.

  std::size_t count = 0;
  std::vector<GEntity *> entities;
  model->getEntities(entities);
  for(std::size_t i = 0; i < entities.size(); i++)
    if(entities[i]->getMeshMaster() != entities[i]) count++;

  if(!count) return;

  fprintf(fp, "$Periodic\n");

  if(binary) { fwrite(&count, sizeof(std::size_t), 1, fp); }
  else {
    fprintf(fp, "%zu\n", count);
  }

  for(std::size_t i = 0; i < entities.size(); i++) {
    GEntity *g_slave = entities[i];
    GEntity *g_master = g_slave->getMeshMaster();

    if(g_slave != g_master) {
      std::map<MVertex *, MVertex *, MVertexPtrLessThan> corrVert;
      corrVert.insert(g_slave->correspondingVertices.begin(),
                      g_slave->correspondingVertices.end());
      if(CTX::instance()->mesh.hoSavePeriodic)
        corrVert.insert(g_slave->correspondingHighOrderVertices.begin(),
                        g_slave->correspondingHighOrderVertices.end());

      if(binary) {
        int gSlaveDim = g_slave->dim();
        int gSlaveTag = g_slave->tag();
        int gMasterTag = g_master->tag();
        fwrite(&gSlaveDim, sizeof(int), 1, fp);
        fwrite(&gSlaveTag, sizeof(int), 1, fp);
        fwrite(&gMasterTag, sizeof(int), 1, fp);

        if(g_slave->affineTransform.size() == 16) {
          std::size_t numAffine = 16;
          fwrite(&numAffine, sizeof(std::size_t), 1, fp);
          for(int j = 0; j < 16; j++) {
            double value = g_slave->affineTransform[j];
            fwrite(&value, sizeof(double), 1, fp);
          }
        }
        else {
          std::size_t numAffine = 0;
          fwrite(&numAffine, sizeof(std::size_t), 1, fp);
        }

        std::size_t corrVertSize = corrVert.size();
        fwrite(&corrVertSize, sizeof(std::size_t), 1, fp);

        for(auto it = corrVert.begin(); it != corrVert.end(); ++it) {
          std::size_t numFirst = it->first->getNum();
          std::size_t numSecond = it->second->getNum();
          fwrite(&numFirst, sizeof(std::size_t), 1, fp);
          fwrite(&numSecond, sizeof(std::size_t), 1, fp);
        }
      }
      else {
        fprintf(fp, "%d %d %d\n", g_slave->dim(), g_slave->tag(),
                g_master->tag());

        if(version >= 4.1) {
          if(g_slave->affineTransform.size() == 16) {
            fprintf(fp, "16");
            for(int j = 0; j < 16; j++)
              fprintf(fp, " %.16g", g_slave->affineTransform[j]);
            fprintf(fp, "\n");
          }
          else {
            fprintf(fp, "0\n");
          }
        }
        else {
          if(g_slave->affineTransform.size() == 16) {
            fprintf(fp, "Affine");
            for(int j = 0; j < 16; j++)
              fprintf(fp, " %.16g", g_slave->affineTransform[j]);
            fprintf(fp, "\n");
          }
        }

        fprintf(fp, "%zu\n", corrVert.size());

        for(auto it = corrVert.begin(); it != corrVert.end(); ++it) {
          fprintf(fp, "%zu %zu\n", it->first->getNum(), it->second->getNum());
        }
      }
    }
  }

  if(binary) fprintf(fp, "\n");
  fprintf(fp, "$EndPeriodic\n");
}

static void writeMSH4GhostCells(GModel *const model, FILE *fp,
                                int partitionToSave, bool binary)
{
  std::vector<GEntity *> entities;
  model->getEntities(entities);
  std::map<MElement *, std::vector<int> > ghostCells;

  for(std::size_t i = 0; i < entities.size(); i++) {
    std::map<MElement *, int> ghostElements;
    int partition = -1;

    if(entities[i]->geomType() == GEntity::GhostCurve) {
      ghostElements = static_cast<ghostEdge *>(entities[i])->getGhostCells();
      partition = static_cast<ghostEdge *>(entities[i])->getPartition();
    }
    else if(entities[i]->geomType() == GEntity::GhostSurface) {
      ghostElements = static_cast<ghostFace *>(entities[i])->getGhostCells();
      partition = static_cast<ghostFace *>(entities[i])->getPartition();
    }
    else if(entities[i]->geomType() == GEntity::GhostVolume) {
      ghostElements = static_cast<ghostRegion *>(entities[i])->getGhostCells();
      partition = static_cast<ghostRegion *>(entities[i])->getPartition();
    }

    if(!partitionToSave || partitionToSave == partition) {
      for(auto it = ghostElements.begin(); it != ghostElements.end(); ++it) {
        if(ghostCells[it->first].size() == 0)
          ghostCells[it->first].push_back(it->second);
        ghostCells[it->first].push_back(partition);
      }
    }
  }

  if(ghostCells.size() != 0) {
    fprintf(fp, "$GhostElements\n");
    if(binary) {
      std::size_t ghostCellsSize = ghostCells.size();
      fwrite(&ghostCellsSize, sizeof(std::size_t), 1, fp);

      for(auto it = ghostCells.begin(); it != ghostCells.end(); ++it) {
        std::size_t elmTag = it->first->getNum();
        int partNum = it->second[0];
        std::size_t numGhostPartitions = it->second.size() - 1;
        fwrite(&elmTag, sizeof(std::size_t), 1, fp);
        fwrite(&partNum, sizeof(int), 1, fp);
        fwrite(&numGhostPartitions, sizeof(std::size_t), 1, fp);
        for(std::size_t i = 1; i < it->second.size(); i++) {
          fwrite(&it->second[i], sizeof(int), 1, fp);
        }
      }
      fprintf(fp, "\n");
    }
    else {
      fprintf(fp, "%ld\n", ghostCells.size());

      for(auto it = ghostCells.begin(); it != ghostCells.end(); ++it) {
        fprintf(fp, "%zu %d %ld", it->first->getNum(), it->second[0],
                it->second.size() - 1);
        for(std::size_t i = 1; i < it->second.size(); i++) {
          fprintf(fp, " %d", it->second[i]);
        }
        fprintf(fp, "\n");
      }
    }
    fprintf(fp, "$EndGhostElements\n");
  }
}

static void writeMSH4Parametrizations(GModel *const model, FILE *fp,
                                      bool binary)
{
  std::size_t nParamE = 0, nParamF = 0;

  for(auto it = model->firstEdge(); it != model->lastEdge(); ++it) {
    discreteEdge *de = dynamic_cast<discreteEdge *>(*it);
    if(de && de->haveParametrization()) { nParamE++; }
  }
  for(auto it = model->firstFace(); it != model->lastFace(); ++it) {
    discreteFace *df = dynamic_cast<discreteFace *>(*it);
    if(df && df->haveParametrization()) { nParamF++; }
  }

  if(!nParamE && !nParamF) return;

  fprintf(fp, "$Parametrizations\n");

  if(binary) {
    fwrite(&nParamE, sizeof(std::size_t), 1, fp);
    fwrite(&nParamF, sizeof(std::size_t), 1, fp);
  }
  else {
    fprintf(fp, "%zu %zu\n", nParamE, nParamF);
  }

  for(auto it = model->firstEdge(); it != model->lastEdge(); ++it) {
    discreteEdge *de = dynamic_cast<discreteEdge *>(*it);
    if(de && de->haveParametrization()) {
      int t = de->tag();
      if(binary)
        fwrite(&t, sizeof(int), 1, fp);
      else
        fprintf(fp, "%d\n", t);
      de->writeParametrization(fp, binary);
    }
  }
  for(auto it = model->firstFace(); it != model->lastFace(); ++it) {
    discreteFace *df = dynamic_cast<discreteFace *>(*it);
    if(df && df->haveParametrization()) {
      int t = df->tag();
      if(binary)
        fwrite(&t, sizeof(int), 1, fp);
      else
        fprintf(fp, "%d\n", t);
      df->writeParametrization(fp, binary);
    }
  }

  if(binary) fprintf(fp, "\n");

  fprintf(fp, "$EndParametrizations\n");
}

int GModel::_writeMSH4(const std::string &name, double version, bool binary,
                       bool saveAll, bool saveParametric, double scalingFactor,
                       bool append, int partitionToSave,
                       std::map<GEntity*, SBoundingBox3d> *entityBounds)
{
  FILE *fp = nullptr;
  if(append)
    fp = Fopen(name.c_str(), binary ? "ab" : "a");
  else
    fp = Fopen(name.c_str(), binary ? "wb" : "w");

  if(!fp) {
    Msg::Error("Unable to open file '%s'", name.c_str());
    return 0;
  }

  if(version < 4.1 && binary) {
    Msg::Error("Can only write MSH 4.0 format in ASCII mode");
    return 0;
  }

  // if there are no physicals we save all the elements
  if(noPhysicalGroups()) saveAll = true;

  // header
  fprintf(fp, "$MeshFormat\n");
  fprintf(fp, "%g %d %zu\n", version, (binary ? 1 : 0), sizeof(std::size_t));
  if(binary) {
    int one = 1;
    fwrite(&one, sizeof(int), 1, fp); // swapping byte
    fprintf(fp, "\n");
  }
  fprintf(fp, "$EndMeshFormat\n");

  // physicals
  if(numPhysicalNames() > 0) {
    fprintf(fp, "$PhysicalNames\n");
    fprintf(fp, "%d\n", numPhysicalNames());
    for(auto it = firstPhysicalName(); it != lastPhysicalName(); ++it) {
      std::string name = it->second;
      if(name.size() > 128) name.resize(128);
      fprintf(fp, "%d %d \"%s\"\n", it->first.first, it->first.second,
              name.c_str());
    }
    fprintf(fp, "$EndPhysicalNames\n");
  }

  // entities
  writeMSH4Entities(this, fp, false, binary, scalingFactor, version,
                    entityBounds);

  // check if the mesh is partitioned... and if we actually have elements in the
  // partitioned entities
  bool partitioned = getNumPartitions() > 0;
  if(partitioned) {
    std::vector<GEntity *> entities;
    getEntities(entities);
    std::size_t partEnt = 0;
    for(auto &ge : entities) {
      if(ge->geomType() == GEntity::PartitionPoint ||
         ge->geomType() == GEntity::PartitionCurve ||
         ge->geomType() == GEntity::PartitionSurface ||
         ge->geomType() == GEntity::PartitionVolume ||
         ge->geomType() == GEntity::GhostCurve ||
         ge->geomType() == GEntity::GhostSurface ||
         ge->geomType() == GEntity::GhostVolume)
        partEnt++;
    }
    if(!partEnt) {
      // this can happen when e.g. loading an old MSH2 files with partition tags
      // stored in elements
      Msg::Warning("No partition entities found, saving mesh as unpartitioned");
      partitioned = false;
    }
  }

  // partitioned entities
  if(partitioned)
    writeMSH4Entities(this, fp, true, binary, scalingFactor, version,
                      entityBounds);

  // nodes
  writeMSH4Nodes(this, fp, partitioned, partitionToSave, binary,
                 saveParametric ? 1 : 0, scalingFactor, saveAll, version);

  // elements
  writeMSH4Elements(this, fp, partitioned, partitionToSave, binary, saveAll,
                    version);

  // periodic
  writeMSH4PeriodicNodes(this, fp, binary, version);

  // ghostCells
  writeMSH4GhostCells(this, fp, partitionToSave, binary);

  // parametrizations
  writeMSH4Parametrizations(this, fp, binary);

  // attributes
  for(auto &a : _attributes) {
    fprintf(fp, "$%s\n", a.first.c_str());
    for(auto &s : a.second) fprintf(fp, "%s\n", s.c_str());
    fprintf(fp, "$End%s\n", a.first.c_str());
  }

  fclose(fp);

  return 1;
}

int GModel::_writePartitionedMSH4(const std::string &baseName, double version,
                                  bool binary, bool saveAll,
                                  bool saveParametric, double scalingFactor)
{
  int nthreads = CTX::instance()->numThreads;
  if(!nthreads) nthreads = Msg::GetMaxThreads();

  // precompute entity bounding boxes (we write the full brep in each file, so
  // otherwise we would compute the bounding boxes as many times as we have
  // partitions)
  std::vector<GEntity*> entities;
  getEntities(entities);
  std::vector<SBoundingBox3d> bounds(entities.size());
#pragma omp parallel for num_threads(nthreads)
  for(std::size_t i = 0; i < entities.size(); i++) {
    bounds[i] = entities[i]->bounds();
  }
  std::map<GEntity*, SBoundingBox3d> entityBounds;
  for(std::size_t i = 0; i < entities.size(); i++) {
    entityBounds[entities[i]] = bounds[i];
  }

  bool exceptions = false;
#pragma omp parallel for num_threads(nthreads)
  for(std::size_t part = 1; part <= getNumPartitions(); part++) {
    if(exceptions) continue;
    std::ostringstream sstream;
    sstream << baseName << "_" << part << ".msh";
    if(getNumPartitions() > 100) {
      if(part % 100 == 1) {
        Msg::Info("Writing partition %d/%d in file '%s'", part, getNumPartitions(),
                  sstream.str().c_str());
      }
    }
    else {
      Msg::Info("Writing partition %d in file '%s'", part, sstream.str().c_str());
    }
    try { // OpenMP forbids leaving block via exception
      _writeMSH4(sstream.str(), version, binary, saveAll, saveParametric,
                 scalingFactor, false, part, &entityBounds);
    }
    catch(...) {
      exceptions = true;
    }
  }

  if(exceptions) throw std::runtime_error(Msg::GetLastError());

  return 1;
}

static bool getPhyscialNameInfo(const std::string &name, int &parentPhysicalTag,
                                std::vector<int> &partitions)
{
  if(name[0] != '_') return false;

  const std::string part = "_part{";
  const std::string physical = "_physical{";

  size_t firstPart = name.find(part) + part.size();
  size_t lastPart = name.find_first_of('}', firstPart);
  const std::string partString = name.substr(firstPart, lastPart - firstPart);

  size_t firstPhysical = name.find(physical) + physical.size();
  size_t lastPhysical = name.find_first_of('}', firstPhysical);
  const std::string physicalString =
    name.substr(firstPhysical, lastPhysical - firstPhysical);

  std::string number;
  for(std::size_t i = 0; i < partString.size(); ++i) {
    if(partString[i] == ',') {
      partitions.push_back(atoi(number.c_str()));
      number.clear();
    }
    else {
      number += partString[i];
    }
  }
  partitions.push_back(atoi(number.c_str()));

  parentPhysicalTag = atoi(physicalString.c_str());

  return true;
}

int GModel::writePartitionedTopology(std::string &name)
{
  Msg::Info("Writing '%s'", name.c_str());

  std::vector<std::map<int, std::pair<int, std::vector<int> > > > allParts(4);
  std::vector<GEntity *> entities;
  getEntities(entities);
  for(std::size_t i = 0; i < entities.size(); i++) {
    std::vector<int> physicals = entities[i]->getPhysicalEntities();
    for(std::size_t j = 0; j < physicals.size(); ++j) {
      const std::string phyName =
        this->getPhysicalName(entities[i]->dim(), physicals[j]);
      int parentPhysicalTag;
      std::vector<int> partitions;
      if(getPhyscialNameInfo(phyName, parentPhysicalTag, partitions)) {
        allParts[entities[i]->dim()].insert
          (std::make_pair(physicals[j],
                          std::make_pair(parentPhysicalTag, partitions)));
      }
    }
  }

  FILE *fp = Fopen(name.c_str(), "w");
  if(!fp) {
    Msg::Error("Could not open file '%s'", name.c_str());
    return 0;
  }

  fprintf(fp, "Group{\n");
  fprintf(fp, "  // Part~{dim}~{parentPhysicalTag}~{part1}~{part2}~...\n\n");
  std::vector<std::map<int, std::string> > tagToString(4);
  for(std::size_t i = 4; i > 0; --i) {
    fprintf(fp, "  // Dim %zu\n", i - 1);
    for(auto it = allParts[i - 1].begin(); it != allParts[i - 1].end(); ++it) {
      std::string partName = "Part~{" + std::to_string(i - 1) + "}~{" +
                             std::to_string(it->second.first) + "}";
      fprintf(fp, "  Part~{%zu}~{%d}", i - 1, it->second.first);
      for(std::size_t j = 0; j < it->second.second.size(); ++j) {
        partName += "~{" + std::to_string(it->second.second[j]) + "}";
        fprintf(fp, "~{%d}", it->second.second[j]);
      }
      tagToString[i - 1].insert(std::make_pair(it->first, partName));
      fprintf(fp, " = Region[{%d}];\n", it->first);
    }
    fprintf(fp, "\n");
  }

  fprintf(fp, "  // Global names\n\n");
  std::map<int, std::vector<int> > omegas;
  std::map<std::pair<int, int>, std::vector<int> > sigmasij;
  std::map<int, std::vector<int> > sigmas;
  std::map<int, std::set<int> > neighbors;
  std::size_t omegaDim = 0;
  for(std::size_t i = 4; i > 0; --i) {
    if(allParts[i - 1].size() != 0) {
      omegaDim = i - 1;
      break;
    }
  }

  // omega
  for(auto it = allParts[omegaDim].begin(); it != allParts[omegaDim].end();
      ++it) {
    if(it->second.second.size() == 1) {
      omegas[it->second.second[0]].push_back(it->first);
    }
  }
  fprintf(fp, "  // Omega\n");
  for(auto it = omegas.begin(); it != omegas.end(); ++it) {
    fprintf(fp, "  Omega~{%d} = Region[{", it->first);
    for(std::size_t j = 0; j < it->second.size(); ++j) {
      if(j == 0)
        fprintf(fp, "%s", tagToString[omegaDim][it->second[j]].c_str());
      else
        fprintf(fp, ", %s", tagToString[omegaDim][it->second[j]].c_str());
    }
    fprintf(fp, "}];\n");
  }
  fprintf(fp, "\n");

  if(omegaDim > 0) {
    // sigma
    for(auto it = allParts[omegaDim - 1].begin();
        it != allParts[omegaDim - 1].end(); ++it) {
      if(it->second.second.size() == 2) {
        sigmasij[std::make_pair(it->second.second[0],
                                it->second.second[1])]
          .push_back(it->first);
        sigmasij[std::make_pair(it->second.second[1],
                                it->second.second[0])]
          .push_back(it->first);
        sigmas[it->second.second[0]].push_back(it->first);
        sigmas[it->second.second[1]].push_back(it->first);
      }
    }
    fprintf(fp, "  // Sigma\n");
    for(auto it = sigmasij.begin(); it != sigmasij.end(); ++it) {
      fprintf(fp, "  Sigma~{%d}~{%d} = Region[{", it->first.first,
              it->first.second);
      for(std::size_t j = 0; j < it->second.size(); ++j) {
        if(j == 0)
          fprintf(fp, "%s", tagToString[omegaDim - 1][it->second[j]].c_str());
        else
          fprintf(fp, ", %s", tagToString[omegaDim - 1][it->second[j]].c_str());
      }
      fprintf(fp, "}];\n");
    }
    fprintf(fp, "\n");

    for(auto it = sigmas.begin(); it != sigmas.end(); ++it) {
      fprintf(fp, "  Sigma~{%d} = Region[{", it->first);
      for(std::size_t j = 0; j < it->second.size(); ++j) {
        if(j == 0)
          fprintf(fp, "%s", tagToString[omegaDim - 1][it->second[j]].c_str());
        else
          fprintf(fp, ", %s", tagToString[omegaDim - 1][it->second[j]].c_str());
      }
      fprintf(fp, "}];\n");
    }
    fprintf(fp, "\n");
  }

  // D
  fprintf(fp, "  D() = {");
  for(std::size_t i = 1; i <= getNumPartitions(); ++i) {
    if(i != 1) fprintf(fp, ", ");
    fprintf(fp, "%zu", i);
  }
  fprintf(fp, "};\n");

  if(omegaDim > 0) {
    // D~{i}
    for(auto it = allParts[omegaDim - 1].begin();
        it != allParts[omegaDim - 1].end(); ++it) {
      if(it->second.second.size() == 2) {
        neighbors[it->second.second[0]].insert(it->second.second[1]);
        neighbors[it->second.second[1]].insert(it->second.second[0]);
      }
    }
    for(std::size_t i = 1; i <= getNumPartitions(); ++i) {
      fprintf(fp, "  D~{%zu}() = {", i);
      for(auto it = neighbors[i].begin(); it != neighbors[i].end(); ++it) {
        if(it != neighbors[i].begin()) fprintf(fp, ", ");
        fprintf(fp, "%d", *it);
      }
      fprintf(fp, "};\n");
    }
  }

  fprintf(fp, "}\n\n");

  fclose(fp);

  Msg::Info("Done writing '%s'", name.c_str());

  return 1;
}
