// Copyright (c) 2011 GeometryFactory Sarl (France)
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org)
//
// $URL: https://github.com/CGAL/cgal/blob/v6.1.1/Filtered_kernel/include/CGAL/Filtered_kernel/internal/Static_filters/Angle_3.h $
// $Id: include/CGAL/Filtered_kernel/internal/Static_filters/Angle_3.h 08b27d3db14 $
// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
//
//
// Author(s)     : Laurent Rineau


#ifndef CGAL_INTERNAL_STATIC_FILTERS_ANGLE_3_H
#define CGAL_INTERNAL_STATIC_FILTERS_ANGLE_3_H

#include <CGAL/Bbox_3.h>
#include <CGAL/Profile_counter.h>
#include <CGAL/Filtered_kernel/internal/Static_filters/Static_filter_error.h>
#include <CGAL/Filtered_kernel/internal/Static_filters/tools.h>
#include <cmath>
#include <iostream>

// inspired from https://people.csail.mit.edu/amy/papers/box-jgt.pdf

namespace CGAL {

namespace internal {

namespace Static_filters_predicates {


template < typename K_base >
class Angle_3
  : public K_base::Angle_3
{
  typedef typename K_base::Angle   Angle;
  typedef typename K_base::Point_3 Point_3;

  typedef typename K_base::Angle_3 Base;

public:
  using Base::operator();

  Sign sign_with_error(const double x, const double error) const {
    if(x > error) return POSITIVE;
    else if( x < - error) return NEGATIVE;
    else return ZERO;
  }

  Angle operator()(const Point_3& p, const Point_3& q, const Point_3& r) const
  {
    CGAL_BRANCH_PROFILER_3("semi-static failures/attempts/calls to   : Angle_3", tmp);

    Get_approx<Point_3> get_approx; // Identity functor for all points
                                    // but lazy points
    double px, py, pz, qx, qy, qz, rx, ry, rz;

    if (fit_in_double(get_approx(p).x(), px) && fit_in_double(get_approx(p).y(), py) &&
        fit_in_double(get_approx(p).z(), pz) &&
        fit_in_double(get_approx(q).x(), qx) && fit_in_double(get_approx(q).y(), qy) &&
        fit_in_double(get_approx(q).z(), qz) &&
        fit_in_double(get_approx(r).x(), rx) && fit_in_double(get_approx(r).y(), ry) &&
        fit_in_double(get_approx(r).z(), rz) )
    {
      CGAL_BRANCH_PROFILER_BRANCH_1(tmp);

      double pqx = px-qx;
      double rqx = rx-qx;
      double pqy = py-qy;
      double rqy = ry-qy;
      double pqz = pz-qz;
      double rqz = rz-qz;

      double maxpq = CGAL::abs(pqx);
      double maxrq = CGAL::abs(rqx);
      double apqy  = CGAL::abs(pqy);
      double arqy  = CGAL::abs(rqy);
      double apqz  = CGAL::abs(pqz);
      double arqz  = CGAL::abs(rqz);

      if(maxpq < apqy) maxpq = apqy;
      if(maxrq < arqy) maxrq = arqy;
      if(maxpq < apqz) maxpq = apqz;
      if(maxrq < arqz) maxrq = arqz;

      if(maxrq < maxpq) std::swap(maxrq, maxpq);
      // then maxrq >= maxpq

      // Protect against underflow in the computation of eps.
      if (maxpq < 1e-146) /* sqrt(min_double/eps) */ {
        if (maxpq == 0)
          return RIGHT;
      }
      // Protect against overflow in the computation of scal.
      else if (maxrq < 7e153) /* sqrt(max_double / 3) */ {
        double scal = pqx * rqx + pqy * rqy + pqz * rqz;

        double eps = 1.6e-15 * maxpq * maxrq;

        if(scal > eps) return ACUTE;
        if(scal < -eps) return OBTUSE;
      }

      CGAL_BRANCH_PROFILER_BRANCH_2(tmp);
    }
    return Base::operator()(p, q, r);
  }


  // Computes the epsilon for Bbox_3_Segment_3_do_intersect.
  static double compute_epsilon()
  {
    typedef Static_filter_error F;
    // F t1 = F(1);
    // F f = ((t1 - t1) * (t1 - t1)) +
    //   ((t1 - t1) * (t1 - t1)) +
    //   ((t1 - t1) * (t1 - t1));
    F t1 = F(1, F::ulp()/2);         // First translation
    F f = t1*t1 + t1*t1 + t1*t1;

    double err = f.error();
    err += err * 2 * F::ulp(); // Correction due to "eps * m * m ".
    std::cerr << "*** epsilon for Angle_3(Point_3, Point_3, Point_3) = "
              << err << std::endl;
    std::cerr << "\n"
              << "Now for underflow/overflows...\n"
              << "       min_double/eps  = "
              << (std::numeric_limits<double>::min)() / err << std::endl
              << "  sqrt(min_double/eps) = "
              << CGAL::sqrt((std::numeric_limits<double>::min)() / err) << std::endl
              << "    sqrt(max_double/3) = "
              << CGAL::sqrt((std::numeric_limits<double>::max)() / 3) << std::endl;
    return err;
  }

}; // end class Angle_3

} // end namespace Static_filters_predicates

} // end namespace internal

} // end namespace CGAL

#endif  // CGAL_INTERNAL_STATIC_FILTERS_ANGLE_3_H
