// SPDX-FileCopyrightText: Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
// SPDX-License-Identifier: BSD-3-Clause

#include <algorithm>
#include <array>
#include <cmath>
#include <sstream>

#include "vtkLine.h"
#include "vtkMath.h"
#include "vtkMinimalStandardRandomSequence.h"
#include "vtkSmartPointer.h"
#include "vtkTriangle.h"

#define VISUAL_DEBUG 0

#ifdef VISUAL_DEBUG
#include <vtkActor.h>
#include <vtkCellArray.h>
#include <vtkDoubleArray.h>
#include <vtkPointData.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkProperty.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>

namespace
{
void DrawTriangles(double* p1, double* q1, double* r1, double* p2, double* q2, double* r2)
{
  // Create a triangle
  vtkSmartPointer<vtkPoints> points = vtkSmartPointer<vtkPoints>::New();
  vtkIdType pid[6];
  pid[0] = points->InsertNextPoint(p1[0], p1[1], p1[2]);
  pid[1] = points->InsertNextPoint(q1[0], q1[1], q1[2]);
  pid[2] = points->InsertNextPoint(r1[0], r1[1], r1[2]);
  pid[3] = points->InsertNextPoint(p2[0], p2[1], p2[2]);
  pid[4] = points->InsertNextPoint(q2[0], q2[1], q2[2]);
  pid[5] = points->InsertNextPoint(r2[0], r2[1], r2[2]);

  vtkSmartPointer<vtkCellArray> verts = vtkSmartPointer<vtkCellArray>::New();
  for (int i = 0; i < 6; i++)
  {
    verts->InsertNextCell(1, &pid[i]);
  }

  vtkSmartPointer<vtkTriangle> triangle1 = vtkSmartPointer<vtkTriangle>::New();
  triangle1->GetPointIds()->SetId(0, 0);
  triangle1->GetPointIds()->SetId(1, 1);
  triangle1->GetPointIds()->SetId(2, 2);

  vtkSmartPointer<vtkTriangle> triangle2 = vtkSmartPointer<vtkTriangle>::New();
  triangle2->GetPointIds()->SetId(0, 3);
  triangle2->GetPointIds()->SetId(1, 4);
  triangle2->GetPointIds()->SetId(2, 5);

  vtkSmartPointer<vtkCellArray> triangles = vtkSmartPointer<vtkCellArray>::New();
  triangles->InsertNextCell(triangle1);
  triangles->InsertNextCell(triangle2);

  vtkSmartPointer<vtkDoubleArray> pointIds = vtkSmartPointer<vtkDoubleArray>::New();
  pointIds->SetNumberOfTuples(6);
  pointIds->SetTuple1(0, 0.);
  pointIds->SetTuple1(1, 1.);
  pointIds->SetTuple1(2, 2.);
  pointIds->SetTuple1(3, 3.);
  pointIds->SetTuple1(4, 4.);
  pointIds->SetTuple1(5, 5.);

  // Create a polydata object
  vtkSmartPointer<vtkPolyData> trianglePolyData = vtkSmartPointer<vtkPolyData>::New();

  // Add the geometry and topology to the polydata
  trianglePolyData->SetPoints(points);
  trianglePolyData->SetVerts(verts);
  trianglePolyData->SetPolys(triangles);
  trianglePolyData->GetPointData()->SetScalars(pointIds);

  // Create mapper and actor
  vtkSmartPointer<vtkPolyDataMapper> mapper = vtkSmartPointer<vtkPolyDataMapper>::New();
  mapper->SetInputData(trianglePolyData);
  mapper->SetScalarRange(0., 5.);
  vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
  actor->SetMapper(mapper);
  actor->GetProperty()->SetPointSize(5);

  // Create a renderer, render window, and an interactor
  vtkSmartPointer<vtkRenderer> renderer = vtkSmartPointer<vtkRenderer>::New();
  vtkSmartPointer<vtkRenderWindow> renderWindow = vtkSmartPointer<vtkRenderWindow>::New();
  renderWindow->AddRenderer(renderer);
  vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
    vtkSmartPointer<vtkRenderWindowInteractor>::New();
  renderWindowInteractor->SetRenderWindow(renderWindow);

  // Add the actors to the scene
  renderer->AddActor(actor);
  renderer->SetBackground(.1, .2, .4); // Background color dark blue

  // Render and interact
  renderWindow->Render();
  renderWindowInteractor->Start();
}
}

#endif

namespace
{
const double EPSILON = 1.e-6;

const int VTK_NO_INTERSECTION = 0;
const int VTK_YES_INTERSECTION = 1;

typedef vtkMinimalStandardRandomSequence vtkRandom;

std::string TriangleToString(double* t1, double* t2, double* t3)
{
  std::stringstream stream;
  stream << "(" << t1[0] << "," << t1[1] << "," << t1[2] << ") (" << t2[0] << "," << t2[1] << ","
         << t2[2] << ") (" << t3[0] << "," << t3[1] << "," << t3[2] << ")";
  return stream.str();
}

void ProjectPointOntoPlane(double* o, double* n, double* p)
{
  // Project point p onto a plane that crosses through point o and has normal n.

  double pMinuso[3];
  vtkMath::Subtract(p, o, pMinuso);

  double dot = vtkMath::Dot(pMinuso, n);

  for (int i = 0; i < 3; i++)
  {
    p[i] -= dot * n[i];
  }
}

void GeneratePointInPlane(vtkRandom* seq, double* o, double* n, double* p)
{
  // Generate a point p that lies in a plane that crosses through point o and
  // has normal n.

  for (int i = 0; i < 3; i++)
  {
    seq->Next();
    p[i] = -1. + 2. * seq->GetValue();
  }

  ProjectPointOntoPlane(o, n, p);
}

void ReflectPointThroughPlane(double* o, double* n, double* p)
{
  // Reflect point p through a plane that crosses through point o and has normal
  // n.

  double dot = 0.;
  for (int i = 0; i < 3; i++)
  {
    dot += (p[i] - o[i]) * n[i];
  }

  for (int i = 0; i < 3; i++)
  {
    p[i] -= dot * n[i];
  }
}

void GeneratePointInHalfPlane(
  vtkRandom* seq, double* o, double* n, double* o2, double* n2, double* p)
{
  // Generate a point p that lies in a plane that crosses through point o, has
  // normal n, and lies on the positive side of the halfspace defined by point
  // o1 and normal n2.

  GeneratePointInPlane(seq, o, n, p);

  double pMinuso2[3];
  vtkMath::Subtract(p, o2, pMinuso2);

  if (vtkMath::Dot(n2, pMinuso2) < 0.)
  {
    ReflectPointThroughPlane(o2, n2, p);
  }
}

void GenerateTriangleInPlane(
  vtkRandom* seq, double* o, double* n, double* t1, double* t2, double* t3)
{
  do
  {
    GeneratePointInPlane(seq, o, n, t1);
    GeneratePointInPlane(seq, o, n, t2);
    GeneratePointInPlane(seq, o, n, t3);
  } while (vtkTriangle::TriangleArea(t1, t2, t3) < EPSILON);
}

void GenerateTriangleInHalfPlane(
  vtkRandom* seq, double* o, double* n, double* o2, double* n2, double* t1, double* t2, double* t3)
{
  do
  {
    GeneratePointInHalfPlane(seq, o, n, o2, n2, t1);
    GeneratePointInHalfPlane(seq, o, n, o2, n2, t2);
    GeneratePointInHalfPlane(seq, o, n, o2, n2, t3);
  } while (vtkTriangle::TriangleArea(t1, t2, t3) < EPSILON);
}

void RandomSphere(vtkRandom* seq, const double radius, const double* offset, double* value)
{
  // Generate a point on a sphere.

  seq->Next();
  double theta = 2. * vtkMath::Pi() * seq->GetValue();
  seq->Next();
  double phi = vtkMath::Pi() * seq->GetValue();
  value[0] = radius * cos(theta) * sin(phi) + offset[0];
  value[1] = radius * sin(theta) * sin(phi) + offset[1];
  value[2] = radius * cos(phi) + offset[2];
}

int TestNegativeResult(vtkRandom* seq, unsigned nTests)
{
  double origin[3] = { 0., 0., 0. };
  double n1[3], n2[3], o1[3], t1[3][3], t2[3][3];

  for (unsigned test = 0; test < nTests; test++)
  {
    RandomSphere(seq, 1, origin, n1);
    RandomSphere(seq, 1, origin, n2);

    for (int i = 0; i < 3; i++)
    {
      seq->Next();
      o1[i] = seq->GetValue();
    }

    GenerateTriangleInPlane(seq, o1, n1, t1[0], t1[1], t1[2]);
    double dividingPlaneOrigin[3];
    for (int i = 0; i < 3; i++)
    {
      dividingPlaneOrigin[i] = t1[0][i] + EPSILON * n1[i];
    }
    GenerateTriangleInHalfPlane(seq, o1, n2, dividingPlaneOrigin, n1, t2[0], t2[1], t2[2]);

    int returnValue = vtkTriangle::TrianglesIntersect(t1[0], t1[1], t1[2], t2[0], t2[1], t2[2]);

    if (returnValue != VTK_NO_INTERSECTION)
    {
      std::cout << "Triangle " << TriangleToString(t1[0], t1[1], t1[2]) << std::endl;
      std::cout << " intersects " << TriangleToString(t2[0], t2[1], t2[2]) << " and shouldn't."
                << std::endl;
#ifdef VISUAL_DEBUG
      DrawTriangles(t1[0], t1[1], t1[2], t2[0], t2[1], t2[2]);
#endif
      return EXIT_FAILURE;
    }
  }

  return EXIT_SUCCESS;
}

int TestCoplanarNegativeResult(vtkRandom* seq, unsigned nTests)
{
  double origin[3] = { 0., 0., 0. };
  double n1[3], n2[3], nn2[3], o1[3], o2[3], t1[3][3], t2[3][3];

  for (unsigned test = 0; test < nTests; test++)
  {
    RandomSphere(seq, 1, origin, n1);
    RandomSphere(seq, 1, origin, n2);

    n1[0] = n1[1] = 0.;
    n1[2] = 1.;

    n2[0] = 1.;
    n2[1] = n2[2] = 0.;

    double dot = vtkMath::Dot(n1, n2);

    for (int i = 0; i < 3; i++)
    {
      n2[i] -= dot * n1[i];
      nn2[i] = -1. * n2[i];
      seq->Next();
      o1[i] = seq->GetValue();
    }

    o1[0] = o1[1] = o1[2] = 1.;

    GeneratePointInPlane(seq, o1, n1, o2);

    o2[0] = o2[1] = 0.;
    o2[2] = 1.;

    double dividingPlaneOrigin[3];
    for (int i = 0; i < 3; i++)
    {
      dividingPlaneOrigin[i] = o2[i] + 10000. * EPSILON * nn2[i];
    }

    GenerateTriangleInHalfPlane(seq, o1, n1, o2, n2, t1[0], t1[1], t1[2]);
    GenerateTriangleInHalfPlane(seq, o1, n1, dividingPlaneOrigin, nn2, t2[0], t2[1], t2[2]);

    int returnValue = vtkTriangle::TrianglesIntersect(t1[0], t1[1], t1[2], t2[0], t2[1], t2[2]);

    if (returnValue != VTK_NO_INTERSECTION)
    {
      std::cout << "Triangle " << TriangleToString(t1[0], t1[1], t1[2]) << std::endl;
      std::cout << " intersects " << TriangleToString(t2[0], t2[1], t2[2]) << " and shouldn't."
                << std::endl;
#ifdef VISUAL_DEBUG
      DrawTriangles(t1[0], t1[1], t1[2], t2[0], t2[1], t2[2]);
#endif
      return EXIT_FAILURE;
    }
  }

  return EXIT_SUCCESS;
}

void ProjectAlongRay(vtkRandom* seq, double* x0, double* x1, double* p)
{
  // Assign point p a value along the ray originating at x0 and passing through
  // x1. The resulting line segment (x0, p) will cross through x1.

  double n[3];
  vtkMath::Subtract(x1, x0, n);
  vtkMath::Normalize(n);

  seq->Next();
  double len = seq->GetValue();
  for (int i = 0; i < 3; i++)
  {
    p[i] = x1[i] + len * n[i];
  }
}

void GenerateOverlappingSegments(
  vtkRandom* seq, double* p1, double* p2, double* x1, double* x2, double* y1, double* y2)
{
  // Given a line through (p1,p2), generate line segments (x1,x2) and (y1,y2)
  // that lie on the line and overlap.

  std::vector<double> random(4, 0.);
  for (int i = 0; i < 4; i++)
  {
    seq->Next();
    random[i] = seq->GetValue();
  }
  std::sort(random.begin(), random.end());

  seq->Next();
  double sequence = seq->GetValue();

  double par[4]; // parametric values for x1,x2,y1,y2

  if (sequence < .25)
  {
    par[0] = random[0];
    par[1] = random[2];
    par[2] = random[1];
    par[3] = random[3];
  }
  else if (sequence < .5)
  {
    par[0] = random[2];
    par[1] = random[0];
    par[2] = random[3];
    par[3] = random[1];
  }
  else if (sequence < .75)
  {
    par[0] = random[0];
    par[1] = random[3];
    par[2] = random[1];
    par[3] = random[2];
  }
  else
  {
    par[0] = random[1];
    par[1] = random[2];
    par[2] = random[0];
    par[3] = random[3];
  }

  for (int i = 0; i < 3; i++)
  {
    x1[i] = p1[i] + par[0] * p2[i];
    x2[i] = p1[i] + par[1] * p2[i];
    y1[i] = p1[i] + par[2] * p2[i];
    y2[i] = p1[i] + par[3] * p2[i];
  }
}

void RandomPoint(vtkRandom* seq, double* p)
{
  // Set p to be a random point in the box (-1,1) x (-1,1) x (-1,1).
  for (int i = 0; i < 3; i++)
  {
    seq->Next();
    p[i] = -1. + 2. * seq->GetValue();
  }
}

int TestPositiveResult(vtkRandom* seq, unsigned nTests)
{
  double p1[3], p2[3], l1[2][3], l2[2][3], t1[3][3], t2[3][3];

  for (unsigned test = 0; test < nTests; test++)
  {
    RandomPoint(seq, p1);
    RandomPoint(seq, p2);
    RandomPoint(seq, t1[0]);
    RandomPoint(seq, t2[0]);

    GenerateOverlappingSegments(seq, p1, p2, l1[0], l1[1], l2[0], l2[1]);

    ProjectAlongRay(seq, t1[0], l1[0], t1[1]);
    ProjectAlongRay(seq, t1[0], l1[1], t1[2]);
    ProjectAlongRay(seq, t2[0], l2[0], t2[1]);
    ProjectAlongRay(seq, t2[0], l2[1], t2[2]);

    int returnValue = vtkTriangle::TrianglesIntersect(t1[0], t1[1], t1[2], t2[0], t2[1], t2[2]);

    if (returnValue != VTK_YES_INTERSECTION)
    {
      std::cout << "Triangle " << TriangleToString(t1[0], t1[1], t1[2]) << std::endl;
      std::cout << " does not intersect " << TriangleToString(t2[0], t2[1], t2[2]) << " and should."
                << std::endl;
#ifdef VISUAL_DEBUG
      DrawTriangles(t1[0], t1[1], t1[2], t2[0], t2[1], t2[2]);
#endif
      return EXIT_FAILURE;
    }
  }

  return EXIT_SUCCESS;
}

int TestCoplanarPositiveResult(vtkRandom* seq, unsigned nTests)
{
  double p1[3], p2[3], l1[2][3], l2[2][3], t1[3][3], t2[3][3], orgn[3], n[3];
  double v1[3], v2[3];

  for (unsigned test = 0; test < nTests; test++)
  {
    RandomPoint(seq, p1);
    RandomPoint(seq, p2);
    RandomPoint(seq, t1[0]);
    RandomPoint(seq, t2[0]);

    GenerateOverlappingSegments(seq, p1, p2, l1[0], l1[1], l2[0], l2[1]);

    ProjectAlongRay(seq, t1[0], l1[0], t1[1]);
    ProjectAlongRay(seq, t1[0], l1[1], t1[2]);
    ProjectAlongRay(seq, t2[0], l2[0], t2[1]);
    ProjectAlongRay(seq, t2[0], l2[1], t2[2]);

    RandomPoint(seq, orgn);

    if (vtkTriangle::TriangleArea(t1[0], t1[1], t1[2]) <
      vtkTriangle::TriangleArea(t2[0], t2[1], t2[2]))
    {
      for (unsigned i = 0; i < 3; i++)
      {
        v1[i] = t1[1][i] - t1[0][i];
        v2[i] = t1[2][i] - t1[0][i];
      }
      vtkMath::Cross(v1, v2, n);
    }
    else
    {
      for (unsigned i = 0; i < 3; i++)
      {
        v1[i] = t2[1][i] - t2[0][i];
        v2[i] = t2[2][i] - t2[0][i];
      }
      vtkMath::Cross(v1, v2, n);
    }
    vtkMath::Normalize(n);

    for (unsigned i = 0; i < 3; i++)
    {
      ProjectPointOntoPlane(orgn, n, t1[i]);
      ProjectPointOntoPlane(orgn, n, t2[i]);
    }

    int returnValue = vtkTriangle::TrianglesIntersect(t1[0], t1[1], t1[2], t2[0], t2[1], t2[2]);

    if (returnValue != VTK_YES_INTERSECTION)
    {
      std::cout << "Triangle " << TriangleToString(t1[0], t1[1], t1[2]) << std::endl;
      std::cout << " does not intersect " << TriangleToString(t2[0], t2[1], t2[2]) << " and should."
                << std::endl;
      return EXIT_FAILURE;
    }
  }

  return EXIT_SUCCESS;
}

int factorial(int n)
{
  return (n == 1 || n == 0) ? 1 : factorial(n - 1) * n;
}

int TestReciprocalResult(vtkRandom* seq, unsigned nTests)
{
  std::array<std::array<double, 3>, 6> p;

  nTests /= factorial(6);

  for (unsigned test = 0; test < nTests; test++)
  {
    for (int i = 0; i < 6; i++)
    {
      RandomPoint(seq, p[i].data());
    }
    std::sort(std::begin(p), std::end(p));
    do
    {
      int returnValue1 = vtkTriangle::TrianglesIntersect(
        p[0].data(), p[1].data(), p[2].data(), p[3].data(), p[4].data(), p[5].data());
      int returnValue2 = vtkTriangle::TrianglesIntersect(
        p[3].data(), p[4].data(), p[5].data(), p[0].data(), p[1].data(), p[2].data());

      if (returnValue1 != returnValue2)
      {
        std::cout << "Triangles " << TriangleToString(p[0].data(), p[1].data(), p[2].data())
                  << " and " << TriangleToString(p[3].data(), p[4].data(), p[5].data())
                  << " disagree about intersection." << std::endl;
        std::cout << "return values: " << returnValue1 << " " << returnValue2 << std::endl;
#ifdef VISUAL_DEBUG
        DrawTriangles(p[0].data(), p[1].data(), p[2].data(), p[3].data(), p[4].data(), p[5].data());
#endif
        return EXIT_FAILURE;
      }
    } while (std::next_permutation(std::begin(p), std::end(p)));
  }

  return EXIT_SUCCESS;
}

int TestIssue17092()
{
  // An instance where triangle intersection failed was reported here:
  // https://gitlab.kitware.com/vtk/vtk/-/issues/17092. It was fixed here:
  // https://gitlab.kitware.com/vtk/vtk/-/merge_requests/3886

  double t1[3][3] = { { 0., 0., 0. }, { 5., 0., 0. }, { 0., 5., 0. } };
  double t2[3][3] = { { 10., 5., 0. }, { 5., 10., 0. }, { 1., 1., 0. } };

  int returnValue = vtkTriangle::TrianglesIntersect(t1[0], t1[1], t1[2], t2[0], t2[1], t2[2]);

  if (returnValue != VTK_YES_INTERSECTION)
  {
    std::cout << "Triangle " << TriangleToString(t1[0], t1[1], t1[2]) << std::endl;
    std::cout << " does not intersect " << TriangleToString(t2[0], t2[1], t2[2]) << " and should."
              << std::endl;
    return EXIT_FAILURE;
  }

  return EXIT_SUCCESS;
}

int TestMR4529()
{
  // An instance where triangle intersection failed (along with its fix) was
  // reported here: https://gitlab.kitware.com/vtk/vtk/-/merge_requests/4529

  double t1[3][3] = { { 1.751, -.993, 0. }, { -3.021, 2.885, 0. }, { 4.14, -4.025, 0. } };
  double t2[3][3] = { { 1.751, -.5, 0. }, { 1.751, 1.326, 0. }, { -3.382, 2.276, 0. } };

  int returnValue = vtkTriangle::TrianglesIntersect(t1[0], t1[1], t1[2], t2[0], t2[1], t2[2]);

  if (returnValue != VTK_YES_INTERSECTION)
  {
    std::cout << "Triangle " << TriangleToString(t1[0], t1[1], t1[2]) << std::endl;
    std::cout << " does not intersect " << TriangleToString(t2[0], t2[1], t2[2]) << " and should."
              << std::endl;
    return EXIT_FAILURE;
  }

  return EXIT_SUCCESS;
}

int TestTriangleIntersection(vtkRandom* seq, unsigned nTests)
{
  if (TestPositiveResult(seq, nTests) == EXIT_FAILURE)
  {
    return EXIT_FAILURE;
  }
  if (TestNegativeResult(seq, nTests) == EXIT_FAILURE)
  {
    return EXIT_FAILURE;
  }
  if (TestCoplanarPositiveResult(seq, nTests) == EXIT_FAILURE)
  {
    return EXIT_FAILURE;
  }
  if (TestCoplanarNegativeResult(seq, nTests) == EXIT_FAILURE)
  {
    return EXIT_FAILURE;
  }
  if (TestReciprocalResult(seq, nTests) == EXIT_FAILURE)
  {
    return EXIT_FAILURE;
  }
  if (TestIssue17092() == EXIT_FAILURE)
  {
    return EXIT_FAILURE;
  }
  if (TestMR4529() == EXIT_FAILURE)
  {
    return EXIT_FAILURE;
  }
  return EXIT_SUCCESS;
}
}

int UnitTestTriangleIntersection(int, char*[])
{
  vtkRandom* sequence = vtkRandom::New();

  sequence->SetSeed(2);

  const unsigned nTest = 1.e5;

  std::cout << "Testing vtkTriangle::TriangleIntersection" << std::endl;
  if (TestTriangleIntersection(sequence, nTest) == EXIT_FAILURE)
  {
    return EXIT_FAILURE;
  }

  sequence->Delete();
  return EXIT_SUCCESS;
}