// Copyright (c) 2024 Max-Planck-Institute Saarbruecken (Germany), GeometryFactory (France)
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org).
//
// $URL: https://github.com/CGAL/cgal/blob/v6.2-beta1/Frechet_distance/include/CGAL/Frechet_distance/internal/Frechet_light.h $
// $Id: include/CGAL/Frechet_distance/internal/Frechet_light.h 431cfb5357d $
// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-Commercial
//
// Author(s)     : André Nusser <anusser@mpi-inf.mpg.de>
//                 Marvin Künnemann <marvin@mpi-inf.mpg.de>
//                 Karl Bringmann <kbringma@mpi-inf.mpg.de>
//                 Andreas Fabri
// =============================================================================

#ifndef CGAL_FRECHET_DISTANCE_INTERNAL_FRECHET_LIGHT_H
#define CGAL_FRECHET_DISTANCE_INTERNAL_FRECHET_LIGHT_H

#include <CGAL/license/Frechet_distance.h>
#include <CGAL/Frechet_distance/internal/Certificate.h>
#include <CGAL/Frechet_distance/internal/Curve.h>
#include <CGAL/Frechet_distance/internal/Filter.h>
#include <CGAL/Frechet_distance/internal/Frechet_light_types.h>
#include <CGAL/Frechet_distance/internal/geometry_basics.h>
#include <CGAL/Frechet_distance/internal/Id.h>
#include <CGAL/Frechet_distance/internal/high_level_predicates.h>


#include <algorithm>
#include <array>
#include <vector>

namespace CGAL {
namespace Frechet_distance {
namespace internal {


/*!
 * \ingroup PkgFrechetDistanceFunctions
 * A class representing a
*/
  template <typename C>
class FrechetLight
{
    using Curve = C;
//    using K = typename Curve::K;
    using Point = typename C::Point;
    using PointID = typename Curve::PointID;
    using distance_t = typename Curve::distance_t;
    using CPoint = CGAL::Frechet_distance::internal::CPoint<C>;
    using CInterval = CGAL::Frechet_distance::internal::CInterval<C>;
    using CIntervals = CGAL::Frechet_distance::internal::CIntervals<C>;
    using CIntervalsID = CGAL::Frechet_distance::internal::CIntervalsID<C>;
    using CPosition = CGAL::Frechet_distance::internal::CPosition<C>;
    using QSimpleInterval = CGAL::Frechet_distance::internal::QSimpleInterval<C>;
    using QSimpleIntervals = CGAL::Frechet_distance::internal::QSimpleIntervals<C>;
    using QSimpleOutputs = CGAL::Frechet_distance::internal::QSimpleOutputs<C>;
    using Certificate = CGAL::Frechet_distance::internal::Certificate<C>;
    using Filter = CGAL::Frechet_distance::internal::Filter<C>;
    using Inputs = CGAL::Frechet_distance::internal::Inputs<C>;
    using Outputs = CGAL::Frechet_distance::internal::Outputs<C>;
    using BoxData = CGAL::Frechet_distance::internal::BoxData<C>;
    using Lambda = CGAL::Frechet_distance::internal::Lambda<C>;
    using CurvePair = std::array<Curve const*, 2>;

public:
    FrechetLight() = default;
    void buildFreespaceDiagram(distance_t const& distance, Curve const& curve1,
                               Curve const& curve2);
    bool lessThan(distance_t const& distance, Curve const& curve1,
                  Curve const& curve2);
    bool lessThanWithFilters(distance_t const& distance, Curve const& curve1,
                             Curve const& curve2);
    std::pair<double,double> calcDistance(Curve const& curve1, Curve const& curve2, double epsilon);
    void clear();

    CurvePair getCurvePair() const;
    Certificate& computeCertificate();
    const Certificate& getCertificate() const { return cert; }

    void setPruningLevel(int pruning_level);
    void setRules(std::array<bool, 5> const& enable);

    std::size_t getNumberOfBoxes() const;

    std::size_t non_filtered = 0;

private:
    CurvePair curve_pair;

    typename Curve::IFT distance;

    std::vector<CIntervals> reachable_intervals_vec;
    QSimpleIntervals qsimple_intervals;
    std::size_t num_boxes;

    // 0 = no pruning ... 6 = full pruning
    int pruning_level = 6;
    // ... and additionally bools to enable/disable rules
    bool enable_box_shrinking = true;
    bool enable_empty_outputs = true;
    bool enable_propagation1 = true;
    bool enable_propagation2 = true;
    bool enable_boundary_rule = true;

#ifdef VIS
    CIntervals unknown_intervals;
    CIntervals connections;
    CIntervals free_non_reachable;
    CIntervals reachable_intervals;

    struct Cell {
        PointID i, j;
        Cell(PointID i, PointID j) : i(i), j(j) {}
    };

    std::vector<Cell> cells;
    std::vector<Cell> const& getCells() const { return cells; }
#endif

    Certificate cert;

  template <class IndexType>
  CInterval getInterval(Curve const& curve1,
                        IndexType const& center_id,
                        Curve const& curve2,
                        PointID seg_start) const
  {
    if constexpr (!std::is_same_v<IndexType, PointID>)
    {
      assert(false);
      return CInterval();
    }
    else
    {
      auto interval = HLPred::intersection_interval(curve1, center_id, curve2, seg_start, distance);
        return CInterval{seg_start, interval.begin, seg_start, interval.end};
    }
  }

    void merge(CIntervals& v, CInterval const& i) const;

    Outputs createFinalOutputs();
    Inputs computeInitialInputs();
    bool isClose(Curve const& curve1, PointID i, Curve const& curve) const;
    CPoint getLastReachablePoint(Curve const& curve1, PointID i,
                                 Curve const& curve2) const;
    bool isTopRightReachable(Outputs const& outputs) const;
    void computeOutputs(Box<C> const& initial_box, Inputs const& initial_inputs,
                        Outputs& final_outputs);

    void getReachableIntervals(BoxData& data);

    // subfunctions of getReachableIntervals
    bool emptyInputsRule(BoxData& data);
    void boxShrinkingRule(BoxData& data);
    void handleCellCase(BoxData& data);
    void getQSimpleIntervals(BoxData& data);
    void calculateQSimple1(BoxData& data);
    void calculateQSimple2(BoxData& data);
    bool boundaryPruningRule(BoxData& data);
    void splitAndRecurse(BoxData& data);

    // intervals used in getReachableIntervals and subfunctions
    CInterval const empty;
    CInterval const* firstinterval1;
    CInterval const* firstinterval2;
    Lambda min1_frac, min2_frac;
    QSimpleInterval qsimple1, qsimple2;
    CInterval out1, out2;
    bool out1_valid = false, out2_valid = false;

    // qsimple interval calculation functions
    QSimpleInterval getTestFullQSimpleInterval(CPoint const& fixed,
                                               const Curve& fixed_curve,
                                               PointID min, PointID max,
                                               const Curve& curve) const;
    // bool updateQSimpleInterval(QSimpleInterval& qsimple, PointID const&
    // fixed, const Curve& fixed_curve, PointID min1, PointID max1, const Curve&
    // curve) const; internal use:
    class TestFullMode;  // mode to test whether simple interval is fill
    class RegularMode;   // mode to obtain complete information
    template <class MODE = RegularMode, typename IndexType = PointID>
    bool updateQSimpleInterval(QSimpleInterval& qsimple, const IndexType& fixed,
                               const Curve& fixed_curve, PointID min1,
                               PointID max1, const Curve& curve) const;
    template <class MODE = RegularMode, typename IndexType = PointID>
    void continueQSimpleSearch(QSimpleInterval& qsimple, const IndexType& fixed,
                               const Curve& fixed_curve, PointID min1,
                               PointID max1, const Curve& curve) const;

    bool isOnLowerRight(const CPosition& pt) const;
    bool isOnUpperLeft(const CPosition& pt) const;

    void initCertificate(Inputs const& initial_inputs);
    void certSetValues(CInterval& interval, CInterval const& parent,
                       PointID point_id, CurveID curve_id);
    void certAddEmpty(CPoint begin, CPoint end, CPoint fixed_point,
                      CurveID fixed_curve);

    // Those are empty function if VIS is not defined
    void visAddReachable(CInterval const& cinterval);
    void visAddUnknown(CPoint begin, CPoint end, CPoint fixed_point,
                       CurveID fixed_curve);
    void visAddConnection(CPoint begin, CPoint end, CPoint fixed_point,
                          CurveID fixed_curve);
    void visAddFreeNonReachable(CPoint begin, CPoint end, CPoint fixed_point,
                                CurveID fixed_curve);
    void visAddCell(Box<C> const& box);

    // Could also be done via getter member functions, but vis is a special
    // case in needing access to the internal structures.
    friend class FreespaceLightVis;
};

template <typename C>
void FrechetLight<C>::certSetValues(CInterval& interval, CInterval const& parent,
                                 PointID point_id, CurveID curve_id)
{
    interval.reach_parent = &parent;
    interval.fixed = CPoint(point_id, 0);
    interval.fixed_curve = curve_id;
}

template <typename C>
void FrechetLight<C>::visAddReachable(CInterval const& cinterval)
{
#ifdef VIS
    if (cinterval.is_empty()) {
        return;
    }
    reachable_intervals.push_back(cinterval);
#else
  CGAL_USE(cinterval);
#endif
}

template <typename C>
void FrechetLight<C>::visAddUnknown(CPoint begin, CPoint end, CPoint fixed_point,
                                 CurveID fixed_curve)
{
#ifdef VIS
    if (begin >= end) {
        return;
    }

    assert(begin >= 0);
    assert(end <= curve_pair[1 - fixed_curve]->size() - 1);

    unknown_intervals.emplace_back(begin, end);
    unknown_intervals.back().fixed = fixed_point;
    unknown_intervals.back().fixed_curve = fixed_curve;

    assert(unknown_intervals.back().begin >= 0);
    assert(unknown_intervals.back().end <=
           curve_pair[1 - unknown_intervals.back().fixed_curve]->size() - 1);
#else
  CGAL_USE(begin);
  CGAL_USE(end);
  CGAL_USE(fixed_point);
  CGAL_USE(fixed_curve);
#endif
}

template <typename C>
void FrechetLight<C>::visAddConnection(CPoint begin, CPoint end,
                                       CPoint fixed_point, CurveID fixed_curve)
{
#ifdef VIS
    if (begin >= end) {
        return;
    }

    assert(begin >= 0);
    assert(end <= curve_pair[1 - fixed_curve]->size() - 1);

    connections.emplace_back(begin, end);
    connections.back().fixed = fixed_point;
    connections.back().fixed_curve = fixed_curve;

    assert(connections.back().begin >= 0);
    assert(connections.back().end <=
           curve_pair[1 - connections.back().fixed_curve]->size() - 1);
#else
  CGAL_USE(begin);
  CGAL_USE(end);
  CGAL_USE(fixed_point);
  CGAL_USE(fixed_curve);
#endif
}

template <typename C>
void FrechetLight<C>::visAddFreeNonReachable(CPoint begin, CPoint end,
                                          CPoint fixed_point,
                                          CurveID fixed_curve)
{
#ifdef VIS
    if (begin >= end) {
        return;
    }

    assert(begin >= 0);
    assert(end <= curve_pair[1 - fixed_curve]->size() - 1);

    free_non_reachable.emplace_back(begin, end);
    free_non_reachable.back().fixed = fixed_point;
    free_non_reachable.back().fixed_curve = fixed_curve;

    assert(free_non_reachable.back().begin >= 0);
    assert(free_non_reachable.back().end <=
           curve_pair[1 - free_non_reachable.back().fixed_curve]->size() - 1);
#else
  CGAL_USE(begin);
  CGAL_USE(end);
  CGAL_USE(fixed_point);
  CGAL_USE(fixed_curve);
#endif
}


template <typename C>
void FrechetLight<C>::merge(CIntervals& intervals,
                                CInterval const& new_interval) const
{
    if (new_interval.is_empty()) {
        return;
    }

    if (!intervals.empty() && new_interval.begin == intervals.back().end) {
        intervals.back().end = new_interval.end;
    } else {
        intervals.emplace_back(new_interval);
    }
}

// TODO: better distinction -- returned SimpleIntervals are only useful to
// determine full/not full

template <typename C>
QSimpleInterval<C> FrechetLight<C>::getTestFullQSimpleInterval(
    CPoint const& fixed, const Curve& fixed_curve, PointID min, PointID max,
    const Curve& curve) const
{
    QSimpleInterval qsimple;
    updateQSimpleInterval<TestFullMode, CPoint>(qsimple, fixed, fixed_curve,
                                                min, max, curve);
    return qsimple;
}

template <typename C>
template <class MODE, class IndexType>
inline bool FrechetLight<C>::updateQSimpleInterval(QSimpleInterval& qsimple,
                                                const IndexType& fixed,
                                                const Curve& fixed_curve,
                                                PointID min, PointID max,
                                                const Curve& curve) const
{
    if (qsimple.is_valid() || (qsimple.hasPartialInformation() &&
                               qsimple.getLastValidPoint() >= max)) {
        qsimple.validate();
        qsimple.clamp(CPoint{min, 0}, CPoint{max, 0});
        return false;  // parent information already valid
    }

    if (qsimple.hasPartialInformation()) {
        if (qsimple.getLastValidPoint() < min) {
            qsimple = QSimpleInterval();  // we know nothing about this part
        } else {
            qsimple.clamp(CPoint{min, 0}, CPoint{max, 0});
            if (!qsimple.getFreeInterval().is_empty()) {
                return false;  // even restricted to current interval, parent
                               // information still gives invalidity
            }
        }
    }

    if (!qsimple.hasPartialInformation()) {  // fresh computation, start with
                                             // heuristics
        // heuristic check:
        auto mid = (min + max) / 2;
        auto maxdist = (CGAL::max)(curve.curve_length(min, mid),
                                   curve.curve_length(mid, max));
        // TODO: return upper bound on error of fixed_point displacement to then
        // overestimate the mid_dist distance.
        // might be a slight improvement but not critical
        auto fixed_point = fixed_curve.interpolate_at(fixed);
        auto mid_dist = Curve::distance(fixed_point, curve[mid], curve.traits());

        // heuristic tests avoiding sqrts
        if (certainly(distance > maxdist)){
          auto comp_dist1 = distance - maxdist;
          if (certainly(mid_dist <= comp_dist1)) { // Uncertain (A)
            qsimple.setFreeInterval(min, max);  // full
            qsimple.validate();

            return true;
          }
        }
        auto comp_dist2 = distance + maxdist;
        if (certainly(mid_dist > comp_dist2)) { // Uncertain (A)
          qsimple.setFreeInterval(max, min);  // empty
          qsimple.validate();

          return true;
        }
    }

    continueQSimpleSearch<MODE, IndexType>(qsimple, fixed, fixed_curve, min,
                                           max, curve);

    return true;
}

template <typename C>
template <class MODE, class IndexType>
inline void FrechetLight<C>::continueQSimpleSearch(QSimpleInterval& qsimple,
                                                const IndexType& fixed,
                                                const Curve& fixed_curve,
                                                PointID min, PointID max,
                                                const Curve& curve) const
{
    assert(!qsimple.hasPartialInformation() ||
           (certainly(qsimple.getLastValidPoint() >= min) &&
            certainly(qsimple.getLastValidPoint() <= max)));  // Uncertain (A)

    PointID start;
    if (qsimple.hasPartialInformation()) {
        start = qsimple.getLastValidPoint();
    } else {
        start = min;
    }

    // Logical assert: there should be no free point in [min, start):
    //  if start > min, then the free interval must be empty

    auto fixed_point = fixed_curve.interpolate_at(fixed);

    // this is an Uncertain
    auto current_free = Curve::distance(fixed_point, curve[start], curve.traits()) <= distance;  // Uncertain (A)
    // If we are not certain if the current node is free, we cannot do anything
    // with interval arithmetic, so we return with an invalid interval.
    if (is_indeterminate(current_free)) {
        qsimple.invalidate();
        return;
    }

    //
    // NOTE: From here on we know that current_free is certain, so we don't have to check. (A)
    //

    // Work directly on the simple_interval of the boundary
    // CPoint first_free = current_free ? CPoint{min,0} : CPoint{max+1,0};
    assert(!current_free || start == min);
    CPoint first_free = current_free
                            ? CPoint{min, 0}
                            : CPoint{max + 1, 0};  // qsimple.free.begin;

    assert(first_free > max ||
           Curve::distance(fixed_point, curve.interpolate_at(first_free), curve.traits()) <= distance); // Uncertain (A)

    std::size_t stepsize = static_cast<std::size_t>(max - start) / 2;
    if (stepsize < 1 || qsimple.hasPartialInformation()) {
        stepsize = 1;
    }
    for (PointID cur = start; cur < max;) {
        // heuristic steps:

        stepsize = std::min<std::size_t>(stepsize, max - cur);
        auto mid = cur + (stepsize + 1) / 2;
        auto maxdist = (CGAL::max)(curve.curve_length(cur, mid),
                                  curve.curve_length(mid, cur + stepsize));
        auto mid_dist = Curve::distance(fixed_point, curve[mid], curve.traits());

        if (current_free && certainly(distance > maxdist) &&               // Uncertain (A)
            certainly(mid_dist <= distance - maxdist)) {
            cur += stepsize;

            stepsize *= 2;
            continue;
        }
        if (!current_free && certainly(mid_dist > distance + maxdist)) { // Uncertain (A)
            cur += stepsize;

            stepsize *= 2;
            continue;
        }
        // if heuristic steps don't work, then reduce stepsize:
        if (stepsize > 1) {
            stepsize /= 2;

            continue;
        }

        // from here on stepsize == 1:
        // mid == end holds in this case
        auto end_dist = mid_dist;
        // if last and next point are both free:
        if (current_free && certainly(end_dist <= distance)) {  // Uncertain (A)
            ++cur;
            stepsize *= 2;

            continue;
        }

        // Now the interval is either not free or the last comparison was inderterminate.
        // In both cases we say that the interval is not full in TestFullMode as we cannot
        // call getInterval with IndexType that is not PointID.
        if (std::is_same<MODE, TestFullMode>::value) {
            return;  // Simple interval is not full -- can return in TestFullMode
        }
        // from here on, regular mode -> IndexType = PointID

        // otherwise we have to compute the intersection interval:
        // TODO: uncritical for correctness or speed but unelegant coding style: stripping down information added by getInterval
        CInterval temp_interval = FrechetLight::getInterval<IndexType>(
            fixed_curve, fixed, curve, cur);

        Interval interval = Interval(temp_interval.begin.getPoint() == cur
                                         ? temp_interval.begin.getFraction()
                                         : 1,
                                     temp_interval.end.getPoint() == cur
                                         ? temp_interval.end.getFraction()
                                         : 1);

        // do previous check for fullness again, but now it is an exact decision
        if (is_zero(interval.begin) && is_one(interval.end)) {  // Uncertain (A)
            assert(current_free);
            ++cur;
            stepsize *= 2;

            continue;
        }
        // from now on we know that the interval is not full

        if (interval.is_empty()) {
            ++cur;
            stepsize *= 2;

            continue;
        }
        // from here on the intersection interval is non-trivial:
        if (!current_free) {
            if (qsimple.is_valid()) {  // we encountered a second free interval
                                       // -> not qsimple
                qsimple.invalidate();
                // still store information in qsimple interval for future use
                qsimple.setLastValidPoint(cur);

                return;
            }

            // if two changes in current interval:
            if ((! is_zero(interval.begin)) && (! is_one(interval.end))) {
                qsimple.setFreeInterval(CPoint{cur, interval.begin},
                                        CPoint{cur, interval.end});
                qsimple.validate();
            } else {  // if one change in current interval:
                first_free = CPoint{cur, interval.begin};
                current_free = true;
            }

            ++cur;
        } else {
            assert(is_zero(interval.begin));  // current_free holds
            assert(! is_one(interval.end));  // end_dist <= distance does not hold, otherwise we
                        // would have stopped before

            qsimple.setFreeInterval(first_free, CPoint{cur, interval.end});
            qsimple.validate();
            current_free = false;
            ++cur;
        }
    }

    // If it is still invalid but we didn't return yet, then the free interval
    // ends at max Note: if no free points were found, first_free defaults to an
    // invalid value (>> max), making the interval empty
    if (!qsimple.is_valid()) {
        qsimple.setFreeInterval(first_free, CPoint{max, 0});
        qsimple.validate();
    }

    return;
}

template <typename C>
typename CIntervals<C>::iterator getIntervalContainingNumber(
    const typename CIntervals<C>::iterator& begin, const typename CIntervals<C>::iterator& end,
    CPoint<C> const& x)
{
    auto it = std::upper_bound(
        begin, end,
        CInterval<C>{x, CPoint<C>{(std::numeric_limits<typename C::PointID::IDType>::max)(), 0}});
    if (it != begin) {
        --it;
        if (it->begin <= x && it->end >= x) {
            return it;
        }
    }
    return end;
}

template <typename C>
typename CIntervals<C>::iterator getIntervalContainingNumber(
    const typename CIntervals<C>::iterator& begin, const typename CIntervals<C>::iterator& end,
    typename C::PointID x)
{
    auto it = std::upper_bound(
        begin, end,
        CInterval<C>{x, 0, (std::numeric_limits<typename C::PointID::IDType>::max)(), 0});
    if (it != begin) {
        --it;
        if (it->begin <= x && it->end >= x) {
            return it;
        }
    }
    return end;
}


template <typename C>
void FrechetLight<C>::getReachableIntervals(BoxData& data)
{
    ++num_boxes;

    auto const& box = data.box;
    auto const& inputs = data.inputs;
    CInterval const empty;

    assert(box.max1 > box.min1 && box.max2 > box.min2);
    // assert(outputs.id1.valid() || outputs.id2.valid());

    firstinterval1 = (inputs.begin1 != inputs.end1) ? &*inputs.begin1 : &empty;
    firstinterval2 = (inputs.begin2 != inputs.end2) ? &*inputs.begin2 : &empty;

    if (emptyInputsRule(data)) {
        return;
    }

    min1_frac = 0, min2_frac = 0;
    boxShrinkingRule(data);

    if (box.isCell()) {
        visAddCell(box);
        handleCellCase(data);
        return;
    } else {
        getQSimpleIntervals(data);
        calculateQSimple1(data);
        calculateQSimple2(data);

        if (out1_valid && out2_valid) {
            return;
        }
        if (boundaryPruningRule(data)) {
            return;
        }

        assert(box.max1 >= box.min1 + 2 || box.max2 >= box.min2 + 2);
        assert(box.max1 >= box.min1 && box.max2 >= box.min2);

        splitAndRecurse(data);
    }
}

template <typename C>
bool FrechetLight<C>::emptyInputsRule(BoxData& data)
{
    auto const& box = data.box;

    // empty input intervals -> empty output intervals
    // Note: if we are currently handling a cell then even if we are not
    // pruning, we have to return with empty outputs for the subsequent code to
    // work.
    if (pruning_level > 0 ||
        (box.min1 == box.max1 - 1 && box.min2 == box.max2 - 1)) {
        if (firstinterval2->is_empty() && firstinterval1->is_empty()) {
            if (data.outputs.id2.valid()) {
                visAddUnknown(CPoint(box.min2, 0), CPoint(box.max2, 0),
                              CPoint(box.max1, 0), 0);
            }
            if (data.outputs.id1.valid()) {
                visAddUnknown(CPoint(box.min1, 0), CPoint(box.max1, 0),
                              CPoint(box.max2, 0), 1);
            }
            return true;
        }
    }

    return false;
}

template <typename C>
void FrechetLight<C>::boxShrinkingRule(BoxData& data)
{
    auto& box = data.box;

    // "movement of input boundary" if one of the inputs is empty
    if (pruning_level > 1 && enable_box_shrinking) {
        if (firstinterval2->is_empty() && firstinterval1->begin > box.min1) {
            auto old_min1 = box.min1;

            min1_frac = firstinterval1->begin.getFraction();
            box.min1 = firstinterval1->begin.getPoint();
            assert(box.min1 <= box.max1);
            if (box.min1 == box.max1) {
                box.min1 = box.max1 - 1;
                min1_frac = 1;
            }

            if (box.min1 != old_min1) {
                visAddUnknown(CPoint(box.min2, 0), CPoint(box.max2, 0),
                              CPoint(box.min1, 0), 0);
                if (data.outputs.id1.valid()) {
                    visAddUnknown(CPoint(old_min1, 0), CPoint(box.min1, 0),
                                  CPoint(box.max2, 0), 1);
                }
            }
        } else if (firstinterval1->is_empty() &&
                   firstinterval2->begin > box.min2) {
            auto old_min2 = box.min2;

            min2_frac = firstinterval2->begin.getFraction();
            box.min2 = firstinterval2->begin.getPoint();
            assert(box.min2 <= box.max2);
            if (box.min2 == box.max2) {
                box.min2 = box.max2 - 1;
                min2_frac = 1;
            }

            if (box.min2 != old_min2) {
                visAddUnknown(CPoint(box.min1, 0), CPoint(box.max1, 0),
                              CPoint(box.min2, 0), 1);
                if (data.outputs.id2.valid()) {
                    visAddUnknown(CPoint(old_min2, 0), CPoint(box.min2, 0),
                                  CPoint(box.max1, 0), 0);
                }
            }
        }
    }
}


template <typename C>
void FrechetLight<C>::handleCellCase(BoxData& data)
{
    auto const& curve1 = *curve_pair[0];
    auto const& curve2 = *curve_pair[1];
    auto const& box = data.box;

    if (data.outputs.id1.valid()) {
        CInterval output1 = getInterval(curve2, box.max2, curve1, box.min1);
        if (firstinterval2->is_empty()) {
            visAddFreeNonReachable(output1.begin,
                                   (std::min)(output1.end, firstinterval1->begin),
                                   {box.max2, 0}, 1);
            output1.begin.setFraction(
                                      (CGAL::max)(output1.begin.getFraction(),
                                                  firstinterval1->begin.getFraction()));
            certSetValues(output1, *firstinterval1, box.max2, 1);
        } else {
            certSetValues(output1, *firstinterval2, box.max2, 1);
        }
        merge(reachable_intervals_vec[data.outputs.id1], output1);
        visAddReachable(output1);
    }

    if (data.outputs.id2.valid()) {
        CInterval output2 = getInterval(curve1, box.max1, curve2, box.min2);
        if (firstinterval1->is_empty()) {
            visAddFreeNonReachable(output2.begin,
                                   (std::min)(output2.end, firstinterval2->begin),
                                   {box.max1, 0}, 0);
            output2.begin.setFraction(
                                      (CGAL::max)(output2.begin.getFraction(),
                                                  firstinterval2->begin.getFraction()));
            certSetValues(output2, *firstinterval2, box.max1, 0);
        } else {
            certSetValues(output2, *firstinterval1, box.max1, 0);
        }
        merge(reachable_intervals_vec[data.outputs.id2], output2);
        visAddReachable(output2);
    }
}


template <typename C>
void FrechetLight<C>::getQSimpleIntervals(BoxData& data)
{
    auto const& curve1 = *curve_pair[0];
    auto const& curve2 = *curve_pair[1];
    auto const& box = data.box;

    qsimple1.invalidate();
    qsimple2.invalidate();

    // Get qsimple intervals. Different cases depending on what has been
    // calculated yet.
    if (data.outputs.id1.valid()) {
        if (data.qsimple_outputs.id1.valid()) {
            qsimple1 = qsimple_intervals[data.qsimple_outputs.id1];
        } else {
            qsimple1 = QSimpleInterval();
        }
        bool changed = updateQSimpleInterval(qsimple1, box.max2, curve2,
                                             box.min1, box.max1, curve1);
        if (changed) {
            qsimple_intervals.push_back(qsimple1);
            data.qsimple_outputs.id1 = qsimple_intervals.size() - 1;
        }
    }
    if (data.outputs.id2.valid()) {
        if (data.qsimple_outputs.id2.valid()) {
            qsimple2 = qsimple_intervals[data.qsimple_outputs.id2];
        } else {
            qsimple2 = QSimpleInterval();
        }
        bool changed = updateQSimpleInterval(qsimple2, box.max1, curve1,
                                             box.min2, box.max2, curve2);
        if (changed) {
            qsimple_intervals.push_back(qsimple2);
            data.qsimple_outputs.id2 = qsimple_intervals.size() - 1;
        }
    }
}

template <typename C>
void FrechetLight<C>::calculateQSimple1(BoxData& data)
{
    auto const& curve1 = *curve_pair[0];
    auto const& curve2 = *curve_pair[1];
    auto const& box = data.box;

    out1_valid = false;
    out1.make_empty();

    // pruning rules depending on qsimple1
    if (qsimple1.is_valid()) {
        // output boundary is empty
        if (qsimple1.is_empty()) {
            // out1 is already empty due to initialization, so leave it.
            if (pruning_level > 2 && enable_empty_outputs) {
                out1_valid = true;
            }
        } else {
            CPoint x =
                (qsimple1.getFreeInterval().begin > CPoint{box.min1, min1_frac})
                    ? qsimple1.getFreeInterval().begin
                    : CPoint{box.min1, min1_frac};
            // check if beginning is reachable
            if (x == box.min1 && pruning_level > 3 && enable_propagation1) {
                typename CIntervals::iterator it =
                getIntervalContainingNumber<C>(
                    data.inputs.begin2, data.inputs.end2, box.max2);
                if (it != data.inputs.end2) {  //(box.min1, box.max2) is
                                               // reachable from interval *it
                    CInterval& parent = *it;
                    out1 = qsimple1.getFreeInterval();
                    out1_valid = true;
                    certSetValues(out1, parent, box.max2, 1);
                }
            }
            // check if nothing can be reachable
            if (x != box.min1 && x > qsimple1.getFreeInterval().end &&
                pruning_level > 4 && enable_propagation2) {
                // out1 is already empty due to initialization, so leave it.
                out1_valid = true;
            }
            // check if we can propagate reachability through the box to the
            // beginning of the free interval
            else if (x > box.min1 && pruning_level > 4 && enable_propagation2) {
                auto it = getIntervalContainingNumber(data.inputs.begin1,
                                                      data.inputs.end1, x);
                if (it !=
                    data.inputs
                        .end1) {  //(x, box.min2) is reachable from interval *it
                    auto interval = getTestFullQSimpleInterval(
                        x, curve1, box.min2, box.max2, curve2);
                    if (interval.is_valid()) {
                        CInterval& parent = *it;
                        out1 = qsimple1.getFreeInterval();
                        out1.begin = x;
                        out1_valid = true;
                        certSetValues(out1, parent, box.max2, 1);
                        visAddConnection({box.min2, 0}, {box.max2, 0}, x, 0);
                    }
                }
            }
        }
    }
    if (out1_valid) {
        merge(reachable_intervals_vec[data.outputs.id1], out1);
        visAddReachable(out1);
        if (!out1.is_empty()) {
            visAddFreeNonReachable(qsimple1.getFreeInterval().begin, out1.begin,
                                   {box.max2, 0}, 1);
        }
        data.outputs.id1.invalidate();
    }
    out1_valid = !data.outputs.id1.valid();
}

template <typename C>
void FrechetLight<C>::calculateQSimple2(BoxData& data)
{
    auto const& curve1 = *curve_pair[0];
    auto const& curve2 = *curve_pair[1];
    auto const& box = data.box;

    out2_valid = false;
    out2.make_empty();

    // pruning rules depending on qsimple2
    if (qsimple2.is_valid()) {
        // output boundary is empty
        if (qsimple2.is_empty()) {
            // out2 is already empty due to initialization, so leave it.
            if (pruning_level > 2 && enable_empty_outputs) {
                out2_valid = true;
            }
        } else {
            CPoint x =
                (qsimple2.getFreeInterval().begin > CPoint{box.min2, min2_frac})
                    ? qsimple2.getFreeInterval().begin
                    : CPoint{box.min2, min2_frac};
            // check if beginning is reachable
            if (x == box.min2 && pruning_level > 3 && enable_propagation1) {
                typename CIntervals::iterator it
                 = getIntervalContainingNumber<C>(
                     data.inputs.begin1, data.inputs.end1, box.max1);
                if (it != data.inputs.end1) {
                    CInterval& parent = *it;
                    out2 = qsimple2.getFreeInterval();
                    out2_valid = true;
                    certSetValues(out2, parent, box.max1, 0);
                }
            }
            // check if nothing can be reachable
            if (x != box.min2 && x > qsimple2.getFreeInterval().end &&
                pruning_level > 4 && enable_propagation2) {
                // out2 is already empty due to initialization, so leave it.
                out2_valid = true;
            }
            // check if we can propagate reachability through the box to the
            // beginning of the free interval
            else if (x > box.min2 && pruning_level > 4 && enable_propagation2) {
                auto it = getIntervalContainingNumber(data.inputs.begin2,
                                                      data.inputs.end2, x);
                if (it != data.inputs.end2) {
                    auto interval = getTestFullQSimpleInterval(
                        x, curve2, box.min1, box.max1, curve1);
                    if (interval.is_valid()) {
                        CInterval& parent = *it;
                        out2 = qsimple2.getFreeInterval();
                        out2.begin = x;
                        out2_valid = true;
                        certSetValues(out2, parent, box.max1, 0);
                        visAddConnection({box.min1, 0}, {box.max1, 0}, x, 1);
                    }
                }
            }
        }
    }
    if (out2_valid) {
        merge(reachable_intervals_vec[data.outputs.id2], out2);
        visAddReachable(out2);
        if (!out2.is_empty()) {
            visAddFreeNonReachable(qsimple2.getFreeInterval().begin, out2.begin,
                                   {box.max1, 0}, 0);
        }
        data.outputs.id2.invalidate();
    }
    out2_valid = !data.outputs.id2.valid();
}


template <typename C>
bool FrechetLight<C>::boundaryPruningRule(BoxData& data)
{
    auto const& curve1 = *curve_pair[0];
    auto const& curve2 = *curve_pair[1];
    auto const& box = data.box;

    // special cases for boxes which are at the boundary of the freespace
    // diagram
    if (pruning_level > 5 && enable_boundary_rule) {
        if (box.max1 == curve1.size() - 1 && out1_valid) {
            visAddUnknown({box.min2, 0}, {box.max2, 0}, {box.max1, 0}, 0);
            return true;
        }
        if (box.max2 == curve2.size() - 1 && out2_valid) {
            visAddUnknown({box.min1, 0}, {box.max1, 0}, {box.max2, 0}, 1);
            return true;
        }
    }

    return false;
}

template <typename C>
void FrechetLight<C>::splitAndRecurse(BoxData& data)
{
    auto const& box = data.box;

    if (box.max2 - box.min2 > box.max1 - box.min1) {  // horizontal split
        reachable_intervals_vec.emplace_back();
        CIntervalsID inputs1_middleID = reachable_intervals_vec.size() - 1;

        PointID split_position = (box.max2 + box.min2) / 2;
        assert(split_position > box.min2 && split_position < box.max2);

        auto bound = CInterval{split_position, 0,
          (std::numeric_limits<typename PointID::IDType>::max)(), 0};
        auto it = std::upper_bound(data.inputs.begin2, data.inputs.end2, bound);

        BoxData data_bottom{
            {box.min1, box.max1, box.min2, split_position},
            {data.inputs.begin1, data.inputs.end1, data.inputs.begin2, it},
            {inputs1_middleID, data.outputs.id2},
            {QSimpleID<C>(), data.qsimple_outputs.id2}};
        getReachableIntervals(data_bottom);

        if (it != data.inputs.begin2 && (it - 1)->end >= split_position) {
            --it;
        }
        CIntervals& inputs1_middle = reachable_intervals_vec[inputs1_middleID];

        BoxData data_top{{box.min1, box.max1, split_position, box.max2},
                         {inputs1_middle.begin(), inputs1_middle.end(), it,
                          data.inputs.end2},
                         {data.outputs.id1, data.outputs.id2},
                         {data.qsimple_outputs.id1, data.qsimple_outputs.id2}};
        getReachableIntervals(data_top);
    } else {  // vertical split
        reachable_intervals_vec.emplace_back();
        CIntervalsID inputs2_middleID = reachable_intervals_vec.size() - 1;

        PointID split_position = (box.max1 + box.min1) / 2;
        assert(split_position > box.min1 && split_position < box.max1);

        auto bound = CInterval{split_position, 0,
                               (std::numeric_limits<typename PointID::IDType>::max)(), 0};
        auto it = std::upper_bound(data.inputs.begin1, data.inputs.end1, bound);

        BoxData data_left{
            {box.min1, split_position, box.min2, box.max2},
            {data.inputs.begin1, it, data.inputs.begin2, data.inputs.end2},
            {data.outputs.id1, inputs2_middleID},
            {data.qsimple_outputs.id1, QSimpleID<C>()}};
        getReachableIntervals(data_left);

        if (it != data.inputs.begin1 && (it - 1)->end >= split_position) {
            --it;
        }
        CIntervals& inputs2_middle = reachable_intervals_vec[inputs2_middleID];

        BoxData data_right{
            {split_position, box.max1, box.min2, box.max2},
            {it, data.inputs.end1, inputs2_middle.begin(),
             inputs2_middle.end()},
            {data.outputs.id1, data.outputs.id2},
            {data.qsimple_outputs.id1, data.qsimple_outputs.id2}};
        getReachableIntervals(data_right);
    }
}

template <typename C>
CPoint<C> FrechetLight<C>::getLastReachablePoint(Curve const& curve1, PointID i,
                                                             Curve const& curve2) const
{
    Point const& point = curve1[i];
    PointID max = curve2.size() - 1;
    std::size_t stepsize = 1;
    for (PointID cur = 0; cur < max;) {
        // heuristic steps:
        stepsize = std::min<std::size_t>(stepsize, max - cur);

        auto mid = cur + (stepsize + 1) / 2;
        auto first_part = curve2.curve_length(cur + 1, mid);
        auto second_part = curve2.curve_length(mid, cur + stepsize);
        auto maxdist = (CGAL::max)(first_part, second_part);
        auto mid_dist = Curve::distance(point, curve2[mid], curve2.traits());


        if(certainly(distance >  maxdist) && (certainly(mid_dist <= distance - maxdist))) { // Uncertain (A)
            cur += stepsize;
            stepsize *= 2;
        }


        // if heuristic steps don't work, then reduce stepsize:
        else if (stepsize > 1) {
            stepsize /= 2;
        } else {
            auto interval = getInterval(curve1, i, curve2, cur);

            // interval is full, so continue
            if (is_one(interval.end.getFraction())) {
                assert(is_zero(interval.begin.getFraction()));
                ++cur;
                stepsize *= 2;
            }

            // the last reachable point is on the current interval
            return interval.end;
        }
    }
    return CPoint{max, 0};
}

/*
template <typename C>
void FrechetLight<C>::buildFreespaceDiagram(distance_t const& distance,
                                            Curve const& curve1,
                                            Curve const& curve2)
{
    this->curve_pair[0] = &curve1;
    this->curve_pair[1] = &curve2;
    this->distance = distance;

    clear();

    Box initial_box(0, curve1.size() - 1, 0, curve2.size() - 1);
    Inputs initial_inputs = computeInitialInputs();
    Outputs final_outputs = createFinalOutputs();

    initCertificate(initial_inputs);

    // this is the main computation of the decision problem
    computeOutputs(initial_box, initial_inputs, final_outputs);
}
*/

template <typename C>
bool FrechetLight<C>::lessThan(distance_t const& d, Curve const& curve1,
                               Curve const& curve2)
{
    this->curve_pair[0] = &curve1;
    this->curve_pair[1] = &curve2;
    this->distance = C::to_ift(d);

    // curves empty or start or end are already far
    if (curve1.empty() || curve2.empty()) {
        return false;
    }
    if (certainly(Curve::distance(curve1.front(), curve2.front(), curve1.traits()) > this->distance)) { // Uncertain (A)
        return false;
    }
    if (certainly(Curve::distance(curve1.back(), curve2.back(), curve1.traits()) > this->distance)) { // Uncertain (A)
        return false;
    }

    // cases where at least one curve has length 1
    if (curve1.size() == 1 && curve2.size() == 1) {
        return true;
    }
    if (curve1.size() == 1) {
        return isClose(curve1, 0, curve2);
    }
    if (curve2.size() == 1) {
        return isClose(curve2, 0, curve1);
    }

    clear();

    Box<C> initial_box(0, curve1.size() - 1, 0, curve2.size() - 1);
    Inputs initial_inputs = computeInitialInputs();
    Outputs final_outputs = createFinalOutputs();

    initCertificate(initial_inputs);

    // this is the main computation of the decision problem
    computeOutputs(initial_box, initial_inputs, final_outputs);

    return isTopRightReachable(final_outputs);
}

template <typename C>
bool FrechetLight<C>::lessThanWithFilters(distance_t const& d, Curve const& curve1,
                                          Curve const& curve2)
{
    this->curve_pair[0] = &curve1;
    this->curve_pair[1] = &curve2;
    this->distance = Curve::to_ift(d);

    assert(curve1.size());
    assert(curve2.size());

    if (certainly(Curve::distance(curve1[0], curve2[0], curve1.traits()) > this->distance) ||          // Uncertain (A)
        certainly(Curve::distance(curve1.back(), curve2.back(), curve1.traits()) > this->distance)) {
        return false;
    }
    if (curve1.size() == 1 && curve2.size() == 1) {
        return true;
    }

    Filter filter(curve1, curve2, this->distance);

    if (filter.bichromaticFarthestDistance()) {
        return true;
    }

    PointID pos1;
    PointID pos2;
    if (filter.adaptiveGreedy(pos1, pos2)) {
        return true;
    }
    if (filter.negative(pos1, pos2)) {
        return false;
    }
    if (filter.adaptiveSimultaneousGreedy()) {
        return true;
    }

    ++non_filtered;

    return lessThan(d, curve1, curve2);
}

template <typename C>
void FrechetLight<C>::computeOutputs(Box<C> const& initial_box,
                                         Inputs const& initial_inputs,
                                         Outputs& final_outputs)
{
    num_boxes = 0;

    BoxData box_data{initial_box, initial_inputs, final_outputs,
                     QSimpleOutputs()};
    getReachableIntervals(box_data);
}

template <typename C>
void FrechetLight<C>::visAddCell(Box<C> const& box)
{
#ifdef VIS
    cells.emplace_back(box.min1, box.min2);
#else
  CGAL_USE(box);
#endif
}

template <typename C>
bool FrechetLight<C>::isClose(Curve const& curve1, PointID i,
                                  Curve const& curve2) const
{
    return getLastReachablePoint(curve1, i, curve2) ==
           CPoint{PointID(curve2.size() - 1), 0};
}

template <typename C>
bool FrechetLight<C>::isTopRightReachable(Outputs const& outputs) const
{
    auto const& curve1 = *curve_pair[0];
    auto const& curve2 = *curve_pair[1];
    auto const& outputs1 = reachable_intervals_vec[outputs.id1];
    auto const& outputs2 = reachable_intervals_vec[outputs.id2];

    return (!outputs1.empty() &&
            (outputs1.back().end.getPoint() == curve1.size() - 1)) ||
           (!outputs2.empty() &&
            (outputs2.back().end.getPoint() == curve2.size() - 1));
}

template <typename C>
void FrechetLight<C>::initCertificate(Inputs const& initial_inputs)
{
    auto const& curve1 = *curve_pair[0];
    auto const& curve2 = *curve_pair[1];

    CInterval origin = CInterval(0, 0);
    certSetValues(origin, origin, 0, -1);
    certSetValues(*initial_inputs.begin1, origin, 0, 1);
    certSetValues(*initial_inputs.begin2, origin, 0, 0);

    visAddUnknown(initial_inputs.begin1->end, CPoint(curve1.size() - 1, 0),
                  {0, 0}, 1);
    visAddUnknown(initial_inputs.begin2->end, CPoint(curve2.size() - 1, 0),
                  {0, 0}, 0);
    visAddReachable(*initial_inputs.begin1);
    visAddReachable(*initial_inputs.begin2);
}

template <typename C>
auto FrechetLight<C>::createFinalOutputs() -> Outputs
{
    Outputs outputs;

    reachable_intervals_vec.emplace_back();
    outputs.id1 = reachable_intervals_vec.size() - 1;
    reachable_intervals_vec.emplace_back();
    outputs.id2 = reachable_intervals_vec.size() - 1;

    return outputs;
}

// this function assumes that the start points of the two curves are close
template <typename C>
auto FrechetLight<C>::computeInitialInputs() -> Inputs
{
    Inputs inputs;

    auto const& curve1 = *curve_pair[0];
    auto const& curve2 = *curve_pair[1];

    auto const first = CPoint(0, 0);

    auto last1 = getLastReachablePoint(curve2, 0, curve1);
    reachable_intervals_vec.emplace_back();
    reachable_intervals_vec.back().emplace_back(first, last1);
    inputs.begin1 = reachable_intervals_vec.back().begin();
    inputs.end1 = reachable_intervals_vec.back().end();

    auto last2 = getLastReachablePoint(curve1, 0, curve2);
    reachable_intervals_vec.emplace_back();
    reachable_intervals_vec.back().emplace_back(first, last2);
    inputs.begin2 = reachable_intervals_vec.back().begin();
    inputs.end2 = reachable_intervals_vec.back().end();

    return inputs;
}

template <typename C>
std::pair<double,double> FrechetLight<C>::calcDistance(Curve const& curve1, Curve const& curve2, double epsilon)
{
  //TODO: In a future version, the epsilon could be an FT type, but for now we keep it simple
    double min = 0;
    double max = curve1.getUpperBoundDistance(curve2);

    while (max - min >= epsilon) {
        auto split = (max + min) / 2.;
        if (lessThan(distance_t(split), curve1, curve2)) {
            max = split;
        } else {
            min = split;
        }
    }

    return std::make_pair(min,max);
}

// This doesn't have to be called but is handy to make time measurements more
// consistent such that the clears in the lessThan call don't have to do
// anything.

template <typename C>
void FrechetLight<C>::clear()
{
    reachable_intervals_vec.clear();
    qsimple_intervals.clear();

#ifdef VIS
    unknown_intervals.clear();
    connections.clear();
    free_non_reachable.clear();
    cells.clear();
    reachable_intervals.clear();
#endif
}

template <typename C>
bool FrechetLight<C>::isOnLowerRight(const CPosition& pt) const
{
    return pt[0] == curve_pair[0]->size() - 1 || pt[1] == 0;
}

template <typename C>
bool FrechetLight<C>::isOnUpperLeft(const CPosition& pt) const
{
    return pt[0] == 0 || pt[1] == curve_pair[1]->size() - 1;
}

// TODO by André: I am not sure whether this is currently fine using interval arithmetic,
// but this only affects the certificates, which are currently not active.
// This needs to be checked in case certificates are used in the future.
template <typename C>
Certificate<C>& FrechetLight<C>::computeCertificate()
{
    cert = Certificate();

    cert.setCurves(curve_pair[0], curve_pair[1]);
    cert.setDistance(distance);

    auto const& curve1 = *curve_pair[0];
    auto const& curve2 = *curve_pair[1];

    // TODO test handling of special cases!
    // special cases:
    if (certainly(Curve::distance(curve1.front(), curve2.front(), curve1.traits()) > distance)) { // Uncertain (A)
        cert.setAnswer(false);
        cert.addPoint({CPoint(0, 0), CPoint(0, 0)});
        cert.validate();
        return cert;
    }
    if (certainly(Curve::distance(curve1.back(), curve2.back(), curve1.traits()) > distance)) { // Uncertain (A)
        cert.setAnswer(false);
        cert.addPoint(
            {CPoint(curve1.size() - 1, 0), CPoint(curve2.size() - 1, 0)});
        cert.validate();
        return cert;
    }

    // cases where at least one curve has length 1
    if (curve1.size() == 1 && curve2.size() == 1) {
        cert.setAnswer(true);
        cert.addPoint({CPoint(0, 0), CPoint(0, 0)});
        cert.validate();
        return cert;
    }
    if (curve1.size() == 1) {
        auto last = getLastReachablePoint(curve1, 0, curve2);
        if (last == CPoint(curve2.size() - 1, 0)) {
            cert.setAnswer(true);
            cert.addPoint({CPoint(0, 0), CPoint(0, 0)});
            cert.addPoint({CPoint(0, 0), CPoint(curve2.size() - 1, 0)});
            cert.validate();
            return cert;
        } else {
            CInterval outer;
            (void)getInterval(curve1, (PointID)0, curve2, last.getPoint());
            CPoint safe_empty = outer.begin > CPoint(last.getPoint(), 0)
                                    ? outer.begin
                                    : outer.end;
            assert(safe_empty > CPoint(last.getPoint(), 0) ||
                   safe_empty < CPoint(last.getPoint() + 1, 0));
            cert.setAnswer(false);
            cert.addPoint({CPoint(0, 0), safe_empty});
            cert.validate();
            return cert;
        }
    }
    if (curve2.size() == 1) {
        auto last = getLastReachablePoint(curve2, 0, curve1);
        if (last == CPoint(curve1.size() - 1, 0)) {
            cert.setAnswer(true);
            cert.addPoint({CPoint(0, 0), CPoint(0, 0)});
            cert.addPoint({CPoint(curve1.size() - 1, 0), CPoint(0, 0)});
            cert.validate();
            return cert;
        } else {
            CInterval outer;
            (void)getInterval(curve2, (PointID)0, curve1, last.getPoint());
            CPoint safe_empty = outer.begin > CPoint(last.getPoint(), 0)
                                    ? outer.begin
                                    : outer.end;
            assert(safe_empty > CPoint(last.getPoint(), 0) ||
                   safe_empty < CPoint(last.getPoint() + 1, 0));
            cert.setAnswer(false);
            cert.addPoint({safe_empty, CPoint(0, 0)});
            cert.validate();
            return cert;
        }
    }

    // TODO: Check for case of a single point!

    CIntervals const& outputs1 = reachable_intervals_vec[2];
    CIntervals const& outputs2 = reachable_intervals_vec[3];

    bool answer = false;
    CInterval const* last_interval;
    if (outputs1.size() &&
        (outputs1.back().end.getPoint() == curve1.size() - 1)) {
        answer = true;
        last_interval = &outputs1.back();
    } else if (outputs2.size() &&
               (outputs2.back().end.getPoint() == curve2.size() - 1)) {
        answer = true;
        last_interval = &outputs2.back();
    }

    cert.setAnswer(answer);

    if (answer) {
        std::vector<CPosition> rev_traversal;
        CPosition cur_pos = {CPoint(curve1.size() - 1, 0),
                             CPoint(curve2.size() - 1, 0)};
        rev_traversal.push_back(cur_pos);
        CInterval const* interval = last_interval;
        while (cur_pos[0] > 0 || cur_pos[1] > 0) {
            CPosition next_pos = {CPoint(0, 0), CPoint(0, 0)};

            next_pos[interval->fixed_curve] = interval->fixed;
            next_pos[1 - interval->fixed_curve] =
                interval->end > cur_pos[1 - interval->fixed_curve]
                    ? cur_pos[1 - interval->fixed_curve]
                    : interval->end;
            assert(next_pos[0] <= cur_pos[0] && next_pos[1] <= cur_pos[1]);
            if (next_pos[0] != cur_pos[0] || next_pos[1] != cur_pos[1]) {
                rev_traversal.push_back(next_pos);
            }

            if (next_pos[1 - interval->fixed_curve] != interval->begin) {
                next_pos[1 - interval->fixed_curve] = interval->begin;
                rev_traversal.push_back(next_pos);
            }

            assert(next_pos[0] <= cur_pos[0] && next_pos[1] <= cur_pos[1]);
            cur_pos = next_pos;
            interval = interval->reach_parent;
        }

        cert.validate();

        for (int t = rev_traversal.size() - 1; t >= 0; t--) {
            cert.addPoint(rev_traversal[t]);
        }
    }

    return cert;
}

template <typename C>
auto FrechetLight<C>::getCurvePair() const -> CurvePair { return curve_pair; }

template <typename C>
void FrechetLight<C>::setPruningLevel(int pruning_level)
{
    this->pruning_level = pruning_level;
}


template <typename C>
void FrechetLight<C>::setRules(std::array<bool, 5> const& enable)
{
    enable_box_shrinking = enable[0];
    enable_empty_outputs = enable[1];
    enable_propagation1 = enable[2];
    enable_propagation2 = enable[3];
    enable_boundary_rule = enable[4];
}

template <typename C>
std::size_t FrechetLight<C>::getNumberOfBoxes() const { return num_boxes; }

} // namespace internal
} // namespace Frechet_distance
} // namespace CGAL

#endif // CGAL_FRECHET_DISTANCE_INTERNAL_FRECHET_LIGHT_H
