// GetDP - Copyright (C) 1997-2018 P. Dular and C. Geuzaine, University of Liege
//
// See the LICENSE.txt file for license information. Please report all
// issues on https://gitlab.onelab.info/getdp/getdp/issues

#include <math.h>
#include "ProData.h"
#include "BF.h"
#include "Message.h"

/* ------------------------------------------------------------------------ */
/*  C a l _ A n a l y t i c I n t e g r a t i o n                           */
/* ------------------------------------------------------------------------ */

double Cal_AnalyticIntegration(struct Element * E,
			       void (*BFEqu)(), void (*BFDof)(),
			       int i, int j, double (*Cal_Productx)())
{
  double DetJ ;

  if ((E->Type != TRIANGLE) ||
      (BFEqu != (void (*)())BF_GradNode) || (BFDof != (void (*)())BF_GradNode) ) {

    Message::Error("Unknown analytic method for integration") ;
    return 0.;
  }

  DetJ = (E->x[2] - E->x[0]) * (E->y[1] - E->y[0]) -
         (E->x[1] - E->x[0]) * (E->y[2] - E->y[0]) ;

  switch (i) {

  case 0 :
    switch (j) {
    case 0 :
      return( ((E->y[2]-E->y[1])*(E->y[2]-E->y[1]) +
	       (E->x[1]-E->x[2])*(E->x[1]-E->x[2])) * fabs(DetJ)
	      / (2. * DetJ * DetJ) ) ;
    case 1 :
      return( ((E->y[2]-E->y[1])*(E->y[0]-E->y[2]) +
	       (E->x[1]-E->x[2])*(E->x[2]-E->x[0])) * fabs(DetJ)
	      / (2. * DetJ * DetJ) ) ;
    case 2 :
      return( ((E->y[2]-E->y[1])*(E->y[1]-E->y[0]) +
	       (E->x[1]-E->x[2])*(E->x[0]-E->x[1])) * fabs(DetJ)
	      / (2. * DetJ * DetJ) ) ;
    default :
      Message::Error("Something wrong in Cal_AnalyticIntegration");
      return 0. ;
    }

  case 1 :
    switch (j) {
    case 0 :
      return( ((E->y[2]-E->y[1])*(E->y[0]-E->y[2]) +
	       (E->x[1]-E->x[2])*(E->x[2]-E->x[0])) * fabs(DetJ)
	      / (2. * DetJ * DetJ) ) ;
    case 1 :
      return( ((E->y[0]-E->y[2])*(E->y[0]-E->y[2]) +
	       (E->x[2]-E->x[0])*(E->x[2]-E->x[0])) * fabs(DetJ)
	      / (2. * DetJ * DetJ) ) ;
    case 2 :
      return( ((E->y[0]-E->y[2])*(E->y[1]-E->y[0]) +
	       (E->x[2]-E->x[0])*(E->x[0]-E->x[1])) * fabs(DetJ)
	      / (2. * DetJ * DetJ) ) ;
    default :
      Message::Error("Something wrong in Cal_AnalyticIntegration");
      return 0. ;
    }

  case 2 :
    switch (j) {
    case 0 :
      return( ((E->y[2]-E->y[1])*(E->y[1]-E->y[0]) +
	       (E->x[1]-E->x[2])*(E->x[0]-E->x[1])) * fabs(DetJ)
	      / (2. * DetJ * DetJ) ) ;
    case 1 :
      return( ((E->y[0]-E->y[2])*(E->y[1]-E->y[0]) +
	       (E->x[2]-E->x[0])*(E->x[0]-E->x[1])) * fabs(DetJ)
	      / (2. * DetJ * DetJ) ) ;
    case 2 :
      return( ((E->y[1]-E->y[0])*(E->y[1]-E->y[0]) +
	       (E->x[0]-E->x[1])*(E->x[0]-E->x[1])) * fabs(DetJ)
	      / (2. * DetJ * DetJ) ) ;
    default :
      Message::Error("Something wrong in Cal_AnalyticIntegration");
      return 0.;
    }

  default :
    Message::Error("Something wrong in Cal_AnalyticIntegration");
    return 0. ;
  }

}
