// SPDX-FileCopyrightText: Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
// SPDX-License-Identifier: BSD-3-Clause
#include "vtkCardinalSpline.h"

#include "vtkObjectFactory.h"
#include "vtkPiecewiseFunction.h"

#include <cassert>
#include <vector>

VTK_ABI_NAMESPACE_BEGIN
vtkStandardNewMacro(vtkCardinalSpline);

//------------------------------------------------------------------------------
// Construct a Cardinal Spline.
vtkCardinalSpline::vtkCardinalSpline() = default;

//------------------------------------------------------------------------------
// Evaluate a 1D Spline
double vtkCardinalSpline::Evaluate(double t)
{
  int index;
  double* intervals;
  double* coefficients;

  // check to see if we need to recompute the spline
  if (this->ComputeTime < this->GetMTime())
  {
    this->Compute();
  }

  // make sure we have at least 2 points
  int size = this->PiecewiseFunction->GetSize();
  if (size < 2)
  {
    return 0.0;
  }

  intervals = this->Intervals;
  coefficients = this->Coefficients;

  if (this->Closed)
  {
    size = size + 1;
  }

  // clamp the function at both ends
  if (t < intervals[0])
  {
    t = intervals[0];
  }
  if (t > intervals[size - 1])
  {
    t = intervals[size - 1];
  }

  // find pointer to cubic spline coefficient using bisection method
  index = this->FindIndex(size, t);

  // calculate offset within interval
  t = (t - intervals[index]);

  // evaluate intervals value y
  return (t *
      (t * (t * *(coefficients + index * 4 + 3) + *(coefficients + index * 4 + 2)) +
        *(coefficients + index * 4 + 1)) +
    *(coefficients + index * 4));
}

//------------------------------------------------------------------------------
// Compute Cardinal Splines for each dependent variable
void vtkCardinalSpline::Compute()
{
  double *ts, *xs;
  std::vector<double> work;
  std::vector<double> dependent;
  double* coefficients;
  int size;
  int i;

  // get the size of the independent variables
  size = this->PiecewiseFunction->GetSize();

  if (size < 2)
  {
    vtkErrorMacro("Cannot compute a spline with less than 2 points. # of points is: " << size);
    return;
  }

  // copy the independent variables. Note that if the spline
  // is closed the first and last point are assumed repeated -
  // so we add and extra point
  delete[] this->Intervals;

  if (!this->Closed)
  {
    this->Intervals = new double[size];
    ts = this->PiecewiseFunction->GetDataPointer();
    for (i = 0; i < size; i++)
    {
      this->Intervals[i] = *(ts + 2 * i);
    }

    // allocate memory for work arrays
    work.resize(size);

    // allocate memory for coefficients
    delete[] this->Coefficients;
    this->Coefficients = new double[4 * size];

    // allocate memory for dependent variables
    dependent.resize(size);

    // get start of coefficients for this dependent variable
    coefficients = this->Coefficients;

    // get the dependent variable values
    xs = this->PiecewiseFunction->GetDataPointer() + 1;
    for (int j = 0; j < size; j++)
    {
      dependent[j] = xs[2 * j];
    }

    this->Fit1D(size, this->Intervals, dependent.data(), work.data(), (double(*)[4])coefficients,
      this->LeftConstraint, this->LeftValue, this->RightConstraint, this->RightValue);
  }

  else // add extra "fictitious" point to close loop
  {
    size = size + 1;
    this->Intervals = new double[size];
    ts = this->PiecewiseFunction->GetDataPointer();
    for (i = 0; i < size - 1; i++)
    {
      this->Intervals[i] = *(ts + 2 * i);
    }
    if (this->ParametricRange[0] != this->ParametricRange[1])
    {
      this->Intervals[size - 1] = this->ParametricRange[1];
    }
    else
    {
      this->Intervals[size - 1] = this->Intervals[size - 2] + 1.0;
    }

    // allocate memory for work arrays
    work.resize(size);

    // allocate memory for coefficients
    delete[] this->Coefficients;
    this->Coefficients = new double[4 * size];

    // allocate memory for dependent variables
    dependent.resize(size);

    // get start of coefficients for this dependent variable
    coefficients = this->Coefficients;

    // get the dependent variable values
    xs = this->PiecewiseFunction->GetDataPointer() + 1;
    for (int j = 0; j < size - 1; j++)
    {
      dependent[j] = xs[2 * j];
    }
    dependent[size - 1] = xs[0];

    this->FitClosed1D(
      size, this->Intervals, dependent.data(), work.data(), (double(*)[4])coefficients);
  }

  // update compute time
  this->ComputeTime = this->GetMTime();
}

//------------------------------------------------------------------------------
// Compute the coefficients for a 1D spline. The spline is open.
void vtkCardinalSpline::Fit1D(int size, double* x, double* y, double* work,
  double coefficients[][4], int leftConstraint, double leftValue, int rightConstraint,
  double rightValue)
{
  double b = 0.0;
  double xlk;
  double xlkp;
  int k;

  // develop constraint at leftmost point.
  switch (leftConstraint)
  {
    case 0:
      // desired slope at leftmost point is derivative from two points
      coefficients[0][1] = 1.0;
      coefficients[0][2] = 0.0;
      work[0] = this->ComputeLeftDerivative();
      break;
    case 1:
      // desired slope at leftmost point is leftValue.
      coefficients[0][1] = 1.0;
      coefficients[0][2] = 0.0;
      work[0] = leftValue;
      break;
    case 2:
      // desired second derivative at leftmost point is leftValue.
      coefficients[0][1] = 2.0;
      coefficients[0][2] = 1.0;
      work[0] = 3.0 * ((y[1] - y[0]) / (x[1] - x[0])) - 0.5 * (x[1] - x[0]) * leftValue;
      break;
    case 3:
      // desired second derivative at leftmost point is
      // leftValue times second derivative at first interior point.
      coefficients[0][1] = 2.0;
      coefficients[0][2] = 4.0 * ((0.5 + leftValue) / (2.0 + leftValue));
      work[0] = 6.0 * ((1.0 + leftValue) / (2.0 + leftValue)) * ((y[1] - y[0]) / (x[1] - x[0]));
      break;
    default:
      assert("check: impossible case." && 0); // reaching this line is a bug.
      break;
  }

  // develop body of band matrix.
  for (k = 1; k < size - 1; k++)
  {
    xlk = x[k] - x[k - 1];
    xlkp = x[k + 1] - x[k];
    coefficients[k][0] = xlkp;
    coefficients[k][1] = 2.0 * (xlkp + xlk);
    coefficients[k][2] = xlk;
    work[k] = 3.0 * (((xlkp * (y[k] - y[k - 1])) / xlk) + ((xlk * (y[k + 1] - y[k])) / xlkp));
  }

  // develop constraint at rightmost point.
  switch (rightConstraint)
  {
    case 0:
      // desired slope at leftmost point is derivative from two points
      coefficients[size - 1][0] = 0.0;
      coefficients[size - 1][1] = 1.0;
      work[size - 1] = this->ComputeRightDerivative();
      break;
    case 1:
      // desired slope at rightmost point is rightValue
      coefficients[size - 1][0] = 0.0;
      coefficients[size - 1][1] = 1.0;
      work[size - 1] = rightValue;
      break;
    case 2:
      // desired second derivative at rightmost point is rightValue.
      coefficients[size - 1][0] = 1.0;
      coefficients[size - 1][1] = 2.0;
      work[size - 1] = 3.0 * ((y[size - 1] - y[size - 2]) / (x[size - 1] - x[size - 2])) +
        0.5 * (x[size - 1] - x[size - 2]) * rightValue;
      break;
    case 3:
      // desired second derivative at rightmost point is
      // rightValue times second derivative at last interior point.
      coefficients[size - 1][0] = 4.0 * ((0.5 + rightValue) / (2.0 + rightValue));
      coefficients[size - 1][1] = 2.0;
      work[size - 1] = 6.0 * ((1.0 + rightValue) / (2.0 + rightValue)) *
        ((y[size - 1] - y[size - 2]) / (x[size - 1] - x[size - 2]));
      break;
    default:
      assert("check: impossible case." && 0); // reaching this line is a bug.
      break;
  }

  // solve resulting set of equations.
  coefficients[0][2] = coefficients[0][2] / coefficients[0][1];
  work[0] = work[0] / coefficients[0][1];
  coefficients[size - 1][2] = 0.0;

  for (k = 1; k < size; k++)
  {
    coefficients[k][1] = coefficients[k][1] - (coefficients[k][0] * coefficients[k - 1][2]);
    coefficients[k][2] = coefficients[k][2] / coefficients[k][1];
    work[k] = (work[k] - (coefficients[k][0] * work[k - 1])) / coefficients[k][1];
  }

  for (k = size - 2; k >= 0; k--)
  {
    work[k] = work[k] - (coefficients[k][2] * work[k + 1]);
  }

  // the column vector work now contains the first
  // derivative of the spline function at each joint.
  // compute the coefficients of the cubic between
  // each pair of joints.
  for (k = 0; k < size - 1; k++)
  {
    b = x[k + 1] - x[k];
    coefficients[k][0] = y[k];
    coefficients[k][1] = work[k];
    coefficients[k][2] = (3.0 * (y[k + 1] - y[k])) / (b * b) - (work[k + 1] + 2.0 * work[k]) / b;
    coefficients[k][3] =
      (2.0 * (y[k] - y[k + 1])) / (b * b * b) + (work[k + 1] + work[k]) / (b * b);
  }

  // the coefficients of a fictitious nth cubic
  // are evaluated.  This may simplify
  // algorithms which include both end points.

  coefficients[size - 1][0] = y[size - 1];
  coefficients[size - 1][1] = work[size - 1];
  coefficients[size - 1][2] = coefficients[size - 2][2] + 3.0 * coefficients[size - 2][3] * b;
  coefficients[size - 1][3] = coefficients[size - 2][3];
}

//------------------------------------------------------------------------------
// Compute the coefficients for a 1D spline. The spline is closed
// (i.e., the first and last point are assumed the same) and the
// spline is continuous in value and derivatives.
void vtkCardinalSpline::FitClosed1D(
  int size, double* x, double* y, double* work, double coefficients[][4])
{
  double b;
  double xlk;
  double xlkp;
  int k;
  double aN, bN, cN, dN;
  int N;

  N = size - 1;

  // develop body of band matrix.
  //
  for (k = 1; k < N; k++)
  {
    xlk = x[k] - x[k - 1];
    xlkp = x[k + 1] - x[k];
    coefficients[k][0] = xlkp;
    coefficients[k][1] = 2.0 * (xlkp + xlk);
    coefficients[k][2] = xlk;
    work[k] = 3.0 * (((xlkp * (y[k] - y[k - 1])) / xlk) + ((xlk * (y[k + 1] - y[k])) / xlkp));
  }

  xlk = x[N] - x[N - 1];
  xlkp = x[1] - x[0];
  aN = coefficients[N][0] = xlkp;
  bN = coefficients[N][1] = 2.0 * (xlkp + xlk);
  cN = coefficients[N][2] = xlk;
  dN = work[N] = 3.0 * (((xlkp * (y[N] - y[N - 1])) / xlk) + ((xlk * (y[1] - y[0])) / xlkp));

  // solve resulting set of equations.
  //
  coefficients[0][2] = 0.0;
  work[0] = 0.0;
  coefficients[0][3] = 1.0;

  for (k = 1; k <= N; k++)
  {
    coefficients[k][1] = coefficients[k][1] - (coefficients[k][0] * coefficients[k - 1][2]);
    coefficients[k][2] = coefficients[k][2] / coefficients[k][1];
    work[k] = (work[k] - (coefficients[k][0] * work[k - 1])) / coefficients[k][1];
    coefficients[k][3] = (-1.0 * coefficients[k][0] * coefficients[k - 1][3]) / coefficients[k][1];
  }

  coefficients[N][0] = 1.0;
  coefficients[N][1] = 0.0;

  for (k = N - 1; k > 0; k--)
  {
    coefficients[k][0] = coefficients[k][3] - coefficients[k][2] * coefficients[k + 1][0];
    coefficients[k][1] = work[k] - coefficients[k][2] * coefficients[k + 1][1];
  }

  work[0] = work[N] = (dN - cN * coefficients[1][1] - aN * coefficients[N - 1][1]) /
    (bN + cN * coefficients[1][0] + aN * coefficients[N - 1][0]);

  for (k = 1; k < N; k++)
  {
    work[k] = coefficients[k][0] * work[N] + coefficients[k][1];
  }

  // the column vector work now contains the first
  // derivative of the spline function at each joint.
  // compute the coefficients of the cubic between
  // each pair of joints.
  for (k = 0; k < N; k++)
  {
    b = x[k + 1] - x[k];
    coefficients[k][0] = y[k];
    coefficients[k][1] = work[k];
    coefficients[k][2] = (3.0 * (y[k + 1] - y[k])) / (b * b) - (work[k + 1] + 2.0 * work[k]) / b;
    coefficients[k][3] =
      (2.0 * (y[k] - y[k + 1])) / (b * b * b) + (work[k + 1] + work[k]) / (b * b);
  }

  // the coefficients of a fictitious nth cubic
  // are the same as the coefficients in the first interval
  //
  coefficients[N][0] = y[N];
  coefficients[N][1] = work[N];
  coefficients[N][2] = coefficients[0][2];
  coefficients[N][3] = coefficients[0][3];
}

//------------------------------------------------------------------------------
void vtkCardinalSpline::DeepCopy(vtkSpline* s)
{
  vtkCardinalSpline* spline = vtkCardinalSpline::SafeDownCast(s);

  if (spline != nullptr)
  {
    // nothing to do
  }

  // Now do superclass
  this->vtkSpline::DeepCopy(s);
}

//------------------------------------------------------------------------------
void vtkCardinalSpline::PrintSelf(ostream& os, vtkIndent indent)
{
  this->Superclass::PrintSelf(os, indent);
}
VTK_ABI_NAMESPACE_END