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 // SPDX-License-Identifier: LGPL-2.1-or-later
 //
 // SPDX-FileCopyrightText: 2016 Akshat Tandon <akshat.tandon@research.iiit.ac.in>
 //
 
 #ifndef MARBLE_NODEREDUCER_H
 #define MARBLE_NODEREDUCER_H
 
 #include "OsmPlacemarkData.h"
 #include "VectorClipper.h"
 
 namespace Marble {
 
 class NodeReducer {
 public:
     NodeReducer(GeoDataDocument* document, const TileId &tileId);
 
     qint64 removedNodes() const;
     qint64 remainingNodes() const;
 
 private:
     qreal epsilonFor(qreal multiplier) const;
     qreal perpendicularDistance(const GeoDataCoordinates &a, const GeoDataCoordinates &b, const GeoDataCoordinates &c) const;
     bool touchesTileBorder(const GeoDataCoordinates &coordinates) const;
 
     GeoDataLinearRing* reducedRing(const GeoDataLinearRing& prevRing,
                                    GeoDataPlacemark* placemark,
                                    const GeoDataPlacemark::GeoDataVisualCategory& visualCategory);
     GeoDataPolygon* reducedPolygon(const GeoDataPolygon& prevPolygon,
                                    GeoDataPlacemark* placemark,
                                    const GeoDataPlacemark::GeoDataVisualCategory& visualCategory);
 
     template<class T>
     void reduce(T const & lineString, OsmPlacemarkData& osmData, GeoDataPlacemark::GeoDataVisualCategory visualCategory, T* reducedLine)
     {
         bool const isArea = lineString.isClosed() && VectorClipper::canBeArea(visualCategory);
         qreal const epsilon = epsilonFor(isArea ? 45.0 : 30.0);
         *reducedLine = douglasPeucker(lineString, osmData, epsilon);
 
         qint64 prevSize = lineString.size();
         qint64 reducedSize = reducedLine->size();
         m_removedNodes += (prevSize - reducedSize);
         m_remainingNodes += reducedSize;
     }
 
     template<class T>
     T extract(T const & lineString, int start, int end) const
     {
         T result;
         for (int i=start; i<=end; ++i) {
             result << lineString[i];
         }
         return result;
     }
 
     template<class T>
     T merge(T const & a, T const &b) const
     {
         T result = a;
         int const index = a.size();
         result << b;
         result.remove(index);
         return result;
     }
 
     template<class T>
     T douglasPeucker(T const & lineString, const OsmPlacemarkData &osmData, qreal epsilon) const
     {
         if (lineString.size() < 3) {
             return lineString;
         }
 
         double maxDistance = 0.0;
         int index = 1;
         int const end = lineString.size()-1;
         for (int i = 1; i<end; ++i) {
             double const distance = perpendicularDistance(lineString[i], lineString[0], lineString[end]);
             if (distance > maxDistance) {
                 index = i;
                 maxDistance = distance;
             }
         }
 
         if (maxDistance >= epsilon) {
             T const left = douglasPeucker(extract(lineString, 0, index), osmData, epsilon);
             T const right = douglasPeucker(extract(lineString, index, end), osmData, epsilon);
             return merge(left, right);
         }
 
         T result;
         result << lineString[0];
         for (int i=1; i<end; ++i) {
             // even if under the Douglas Peucker threshold, we keep the following nodes:
             // - nodes at a tile border
             // - nodes containing any OSM tag themselves
             // - nodes adjacent to synthetic nodes introduced by clipping. This is to avoid
             //   synthetic only line segments that geometry reassembly on the client might
             //   remove entirely and thus distort the original geometry.
             bool const keepNode = touchesTileBorder(lineString[i]) || !osmData.nodeReference(lineString[i]).isEmpty()
                 || osmData.nodeReference(lineString[i-1]).id() < 0 || ((i + 1) < end && osmData.nodeReference(lineString[i+1]).id() < 0);
             if (keepNode) {
                 result << lineString[i];
             }
         }
         result << lineString[end];
         return result;
     }
 
     qint64 m_removedNodes;
     qint64 m_remainingNodes;
 
     int m_zoomLevel;
     double m_tileBoundary[4];
     enum Boundary {
         West = 0,
         North = 1,
         East = 2,
         South = 3
     };
 };
 
 }
 
 #endif