// Gmsh - Copyright (C) 1997-2021 C. Geuzaine, J.-F. Remacle
//
// See the LICENSE.txt file for license information. Please report all
// issues on https://gitlab.onelab.info/gmsh/gmsh/issues.

#include <math.h>
#include "GaussIntegration.h"
#include "GaussLegendre1D.h"

static void brickToTet(double xi, double eta, double zeta, double *r, double *s,
                       double *t, double *J)
{
  double r1, rs1;
  *r = 0.5e0 * (1.0e0 + xi);
  r1 = 1.0e0 - (*r);
  *s = 0.5e0 * (1.0e0 + eta) * r1;
  rs1 = 1.0e0 - (*r) - (*s);
  *t = 0.5e0 * (1.0e0 + zeta) * rs1;
  *J = 0.125e0 * r1 * rs1;
}

void quadToTri(double xi, double eta, double *r, double *s, double *J)
{
  double r1;
  *r = 0.5e0 * (1.0e0 + xi);
  r1 = 1.0e0 - (*r);
  *s = 0.5e0 * (1.0e0 + eta) * r1;
  *J = 0.25e0 * r1;
}

double quadToTriJac(double, double eta) { return 0.125e0 * (1.0e0 - eta); }

int GaussLegendreTet(int n1, int n2, int n3, IntPt *pts)
{
  /* get degenerate n1Xn2Xn3 Gauss-Legendre scheme to integrate over a tet */
  int i, j, k, index = 0;
  double *pt1, *pt2, *pt3, *wt1, *wt2, *wt3, dJ;

  gmshGaussLegendre1D(n1, &pt1, &wt1);
  gmshGaussLegendre1D(n2, &pt2, &wt2);
  gmshGaussLegendre1D(n3, &pt3, &wt3);
  for(i = 0; i < n1; i++) {
    for(j = 0; j < n2; j++) {
      for(k = 0; k < n3; k++) {
        brickToTet(pt1[i], pt2[j], pt3[k], &(pts[index].pt[0]),
                   &(pts[index].pt[1]), &(pts[index].pt[2]), &dJ);
        pts[index++].weight = dJ * wt1[i] * wt2[j] * wt3[k];
      }
    }
  }
  return index;
}

int GaussLegendreTri(int n1, int n2, IntPt *pts)
{
  /* get degenerate n1Xn2 Gauss-Legendre scheme to integrate over a tri */
  int i, j, index = 0;
  double *pt1, *pt2, *wt1, *wt2, dJ;
  // const double two = 2.0000000000000000;

  gmshGaussLegendre1D(n1, &pt1, &wt1);
  gmshGaussLegendre1D(n2, &pt2, &wt2);
  for(i = 0; i < n1; i++) {
    for(j = 0; j < n2; j++) {
      quadToTri(pt1[i], pt2[j], &(pts[index].pt[0]), &(pts[index].pt[1]), &dJ);
      pts[index].pt[2] = 0;
      pts[index++].weight = dJ * wt1[i] * wt2[j];
    }
  }
  return index;
}
