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/** @file Implementation of the post processing step to invert
 * all normals in meshes with infacing normals.
 */

// internal headers
#include "FixNormalsStep.h"
#include <assimp/StringUtils.h>
#include <assimp/DefaultLogger.hpp>
#include <assimp/postprocess.h>
#include <assimp/scene.h>
#include <stdio.h>


using namespace Assimp;


// ------------------------------------------------------------------------------------------------
// Constructor to be privately used by Importer
FixInfacingNormalsProcess::FixInfacingNormalsProcess() = default;

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

// ------------------------------------------------------------------------------------------------
// Returns whether the processing step is present in the given flag field.
bool FixInfacingNormalsProcess::IsActive( unsigned int pFlags) const
{
 return (pFlags & aiProcess_FixInfacingNormals) != 0;
}

// ------------------------------------------------------------------------------------------------
// Executes the post processing step on the given imported data.
void FixInfacingNormalsProcess::Execute( aiScene* pScene)
{
 ASSIMP_LOG_DEBUG("FixInfacingNormalsProcess begin");

 bool bHas( false );
 for (unsigned int a = 0; a < pScene->mNumMeshes; ++a) {
 if (ProcessMesh(pScene->mMeshes[a], a)) {
 bHas = true;
 }
 }

 if (bHas) {
 ASSIMP_LOG_DEBUG("FixInfacingNormalsProcess finished. Found issues.");
 } else {
 ASSIMP_LOG_DEBUG("FixInfacingNormalsProcess finished. No changes to the scene.");
 }
}

// ------------------------------------------------------------------------------------------------
// Apply the step to the mesh
bool FixInfacingNormalsProcess::ProcessMesh( aiMesh* pcMesh, unsigned int index)
{
 ai_assert(nullptr != pcMesh);

 // Nothing to do if there are no model normals
 if (!pcMesh->HasNormals()) {
 return false;
 }

 // Compute the bounding box of both the model vertices + normals and
 // the unmodified model vertices. Then check whether the first BB
 // is smaller than the second. In this case we can assume that the
 // normals need to be flipped, although there are a few special cases ..
 // convex, concave, planar models ...

 aiVector3D vMin0 (1e10f,1e10f,1e10f);
 aiVector3D vMin1 (1e10f,1e10f,1e10f);
 aiVector3D vMax0 (-1e10f,-1e10f,-1e10f);
 aiVector3D vMax1 (-1e10f,-1e10f,-1e10f);

 for (unsigned int i = 0; i < pcMesh->mNumVertices;++i)
 {
 vMin1.x = std::min(vMin1.x,pcMesh->mVertices[i].x);
 vMin1.y = std::min(vMin1.y,pcMesh->mVertices[i].y);
 vMin1.z = std::min(vMin1.z,pcMesh->mVertices[i].z);

 vMax1.x = std::max(vMax1.x,pcMesh->mVertices[i].x);
 vMax1.y = std::max(vMax1.y,pcMesh->mVertices[i].y);
 vMax1.z = std::max(vMax1.z,pcMesh->mVertices[i].z);

 const aiVector3D vWithNormal = pcMesh->mVertices[i] + pcMesh->mNormals[i];

 vMin0.x = std::min(vMin0.x,vWithNormal.x);
 vMin0.y = std::min(vMin0.y,vWithNormal.y);
 vMin0.z = std::min(vMin0.z,vWithNormal.z);

 vMax0.x = std::max(vMax0.x,vWithNormal.x);
 vMax0.y = std::max(vMax0.y,vWithNormal.y);
 vMax0.z = std::max(vMax0.z,vWithNormal.z);
 }

 const float fDelta0_x = (vMax0.x - vMin0.x);
 const float fDelta0_y = (vMax0.y - vMin0.y);
 const float fDelta0_z = (vMax0.z - vMin0.z);

 const float fDelta1_x = (vMax1.x - vMin1.x);
 const float fDelta1_y = (vMax1.y - vMin1.y);
 const float fDelta1_z = (vMax1.z - vMin1.z);

 // Check whether the boxes are overlapping
 if ((fDelta0_x > 0.0f) != (fDelta1_x > 0.0f))return false;
 if ((fDelta0_y > 0.0f) != (fDelta1_y > 0.0f))return false;
 if ((fDelta0_z > 0.0f) != (fDelta1_z > 0.0f))return false;

 // Check whether this is a planar surface
 const float fDelta1_yz = fDelta1_y * fDelta1_z;

 if (fDelta1_x < 0.05f * std::sqrt( fDelta1_yz ))return false;
 if (fDelta1_y < 0.05f * std::sqrt( fDelta1_z * fDelta1_x ))return false;
 if (fDelta1_z < 0.05f * std::sqrt( fDelta1_y * fDelta1_x ))return false;

 // now compare the volumes of the bounding boxes
 if (std::fabs(fDelta0_x * fDelta0_y * fDelta0_z) < std::fabs(fDelta1_x * fDelta1_yz)) {
 if (!DefaultLogger::isNullLogger()) {
 ASSIMP_LOG_INFO("Mesh ", index, ": Normals are facing inwards (or the mesh is planar)", index);
 }

 // Invert normals
 for (unsigned int i = 0; i < pcMesh->mNumVertices;++i)
 pcMesh->mNormals[i] *= -1.0f;

 // ... and flip faces
 for (unsigned int i = 0; i < pcMesh->mNumFaces;++i)
 {
 aiFace& face = pcMesh->mFaces[i];
 for( unsigned int b = 0; b < face.mNumIndices / 2; b++)
 std::swap( face.mIndices[b], face.mIndices[ face.mNumIndices - 1 - b]);
 }
 return true;
 }
 return false;
}