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

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

#include <vector>

VTK_ABI_NAMESPACE_BEGIN
vtkStandardNewMacro(vtkKochanekSpline);

//------------------------------------------------------------------------------
// Construct a KochanekSpline with the following defaults:
// DefaultBias = 0,
// DefaultTension = 0,
// DefaultContinuity = 0.
vtkKochanekSpline::vtkKochanekSpline()
{
  this->DefaultBias = 0.0;
  this->DefaultTension = 0.0;
  this->DefaultContinuity = 0.0;
}

//------------------------------------------------------------------------------
// Evaluate a 1D Spline
double vtkKochanekSpline::Evaluate(double t)
{
  int index = 0;
  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
  index = this->FindIndex(size, t);

  // calculate offset within interval
  t = (t - intervals[index]) / (intervals[index + 1] - intervals[index]);

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

//------------------------------------------------------------------------------
// Compute Kochanek Spline coefficients.
void vtkKochanekSpline::Compute()
{
  double *ts, *xs;
  double* coefficients;
  std::vector<double> dependent;
  int size;
  int i;

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

  if (size < 2)
  {
    vtkErrorMacro("Spline requires at least 2 points. # of points is: " << size);
    return;
  }

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

    // 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];
    }
  }
  else // spline is closed, create extra "fictitious" point
  {
    size = size + 1;
    // copy the independent variables
    delete[] this->Intervals;
    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 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->Fit1D(size, this->Intervals, dependent.data(), this->DefaultTension, this->DefaultBias,
    this->DefaultContinuity, (double(*)[4])coefficients, this->LeftConstraint, this->LeftValue,
    this->RightConstraint, this->RightValue);

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

#define VTK_EPSILON .0001

//------------------------------------------------------------------------------
// Compute the coefficients for a 1D spline
void vtkKochanekSpline::Fit1D(int size, double* x, double* y, double tension, double bias,
  double continuity, double coefficients[][4], int leftConstraint, double leftValue,
  int rightConstraint, double rightValue)
{
  double cs;     /* source chord                 */
  double cd;     /* destination chord            */
  double ds;     /* source deriviative           */
  double dd;     /* destination deriviative      */
  double n0, n1; /* number of frames btwn nodes  */
  int N;         /* top point number             */
  int i;

  N = size - 1;

  for (i = 1; i < N; i++)
  {
    cs = y[i] - y[i - 1];
    cd = y[i + 1] - y[i];

    ds = cs * ((1 - tension) * (1 - continuity) * (1 + bias)) / 2.0 +
      cd * ((1 - tension) * (1 + continuity) * (1 - bias)) / 2.0;

    dd = cs * ((1 - tension) * (1 + continuity) * (1 + bias)) / 2.0 +
      cd * ((1 - tension) * (1 - continuity) * (1 - bias)) / 2.0;

    // adjust deriviatives for non uniform spacing between nodes
    n1 = x[i + 1] - x[i];
    n0 = x[i] - x[i - 1];

    ds *= (2 * n0 / (n0 + n1));
    dd *= (2 * n1 / (n0 + n1));

    coefficients[i][0] = y[i];
    coefficients[i][1] = dd;
    coefficients[i][2] = ds;
  }

  // Calculate the deriviatives at the end points
  coefficients[0][0] = y[0];
  coefficients[N][0] = y[N];
  coefficients[N][1] = 0.0;
  coefficients[N][2] = 0.0;
  coefficients[N][3] = 0.0;

  if (this->Closed) // the curve is continuous and closed at P0=Pn
  {
    cs = y[N] - y[N - 1];
    cd = y[1] - y[0];

    ds = cs * ((1 - tension) * (1 - continuity) * (1 + bias)) / 2.0 +
      cd * ((1 - tension) * (1 + continuity) * (1 - bias)) / 2.0;

    dd = cs * ((1 - tension) * (1 + continuity) * (1 + bias)) / 2.0 +
      cd * ((1 - tension) * (1 - continuity) * (1 - bias)) / 2.0;

    // adjust deriviatives for non uniform spacing between nodes
    n1 = x[1] - x[0];
    n0 = x[N] - x[N - 1];
    ds *= (2 * n0 / (n0 + n1));
    dd *= (2 * n1 / (n0 + n1));

    coefficients[0][1] = dd;
    coefficients[0][2] = ds;
    coefficients[N][1] = dd;
    coefficients[N][2] = ds;
  }
  else // curve is open
  {
    switch (leftConstraint)
    {
      case 0:
        // desired slope at leftmost point is leftValue
        coefficients[0][1] = this->ComputeLeftDerivative();
        break;

      case 1:
        // desired slope at leftmost point is leftValue
        coefficients[0][1] = leftValue;
        break;

      case 2:
        // desired second derivative at leftmost point is leftValue
        coefficients[0][1] = (6 * (y[1] - y[0]) - 2 * coefficients[1][2] - leftValue) / 4.0;
        break;

      case 3:
        // desired second derivative at leftmost point is leftValue
        // times second derivative at first interior point
        if ((leftValue > (-2.0 + VTK_EPSILON)) || (leftValue < (-2.0 - VTK_EPSILON)))
        {
          coefficients[0][1] =
            (3 * (1 + leftValue) * (y[1] - y[0]) - (1 + 2 * leftValue) * coefficients[1][2]) /
            (2 + leftValue);
        }
        else
        {
          coefficients[0][1] = 0.0;
        }
        break;
    }

    switch (rightConstraint)
    {
      case 0:
        // desired slope at rightmost point is rightValue
        coefficients[N][2] = this->ComputeRightDerivative();
        break;

      case 1:
        // desired slope at rightmost point is rightValue
        coefficients[N][2] = rightValue;
        break;

      case 2:
        // desired second derivative at rightmost point is rightValue
        coefficients[N][2] =
          (6 * (y[N] - y[N - 1]) - 2 * coefficients[N - 1][1] + rightValue) / 4.0;
        break;

      case 3:
        // desired second derivative at rightmost point is rightValue
        // times second derivative at last interior point
        if ((rightValue > (-2.0 + VTK_EPSILON)) || (rightValue < (-2.0 - VTK_EPSILON)))
        {
          coefficients[N][2] = (3 * (1 + rightValue) * (y[N] - y[N - 1]) -
                                 (1 + 2 * rightValue) * coefficients[N - 1][1]) /
            (2 + rightValue);
        }
        else
        {
          coefficients[N][2] = 0.0;
        }
        break;
    }
  } // curve is open

  // Compute the Coefficients
  for (i = 0; i < N; i++)
  {
    //
    // c0    = P ;    c1    = DD ;
    //   i      i       i       i
    //
    // c1    = P   ;  c2    = DS   ;
    //   i+1    i+1     i+1     i+1
    //
    // c2  = -3P  + 3P    - 2DD  - DS   ;
    //   i      i     i+1      i     i+1
    //
    // c3  =  2P  - 2P    +  DD  + DS   ;
    //   i      i     i+1      i     i+1
    //
    coefficients[i][2] =
      (-3 * y[i]) + (3 * y[i + 1]) + (-2 * coefficients[i][1]) + (-1 * coefficients[i + 1][2]);
    coefficients[i][3] =
      (2 * y[i]) + (-2 * y[i + 1]) + (1 * coefficients[i][1]) + (1 * coefficients[i + 1][2]);
  }
}

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

  if (spline != nullptr)
  {
    this->DefaultBias = spline->DefaultBias;
    this->DefaultTension = spline->DefaultTension;
    this->DefaultContinuity = spline->DefaultContinuity;
  }

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

//------------------------------------------------------------------------------
void vtkKochanekSpline::PrintSelf(ostream& os, vtkIndent indent)
{
  this->Superclass::PrintSelf(os, indent);
  os << indent << "DefaultBias: " << this->DefaultBias << "\n";
  os << indent << "DefaultTension: " << this->DefaultTension << "\n";
  os << indent << "DefaultContinuity: " << this->DefaultContinuity << "\n";
}
VTK_ABI_NAMESPACE_END