/**********************************************************************

 *

 * GEOS - Geometry Engine Open Source

 * http://geos.osgeo.org

 *

 * Copyright (C) 2013 Sandro Santilli <strk@kbt.io>

 *

 * This is free software; you can redistribute and/or modify it under

 * the terms of the GNU Lesser General Public Licence as published

 * by the Free Software Foundation.

 * See the COPYING file for more information.

 *

 **********************************************************************

 *

 * Last port: algorithm/Centroid.java r728 (JTS-0.13+)

 *

 **********************************************************************/

#pragma once

#include <geos/export.h>

#include <geos/geom/Coordinate.h> // for composition

#include <memory> // for std::unique_ptr

// Forward declarations

namespace geos {

namespace geom {

class Geometry;

class Polygon;

class CoordinateSequence;

}

}

namespace geos {

namespace algorithm { // geos::algorithm

/** \brief

 * Computes the centroid of a [Geometry](@ref geom::Geometry) of any dimension.

 *

 * If the geometry is nomimally of higher dimension, but contains only

 * components having a lower effective dimension (i.e. zero length or area),

 * the centroid will be computed appropriately.

 *

 * ### Algorithm #

 *

 * - **Dimension = 2** - Based on the usual algorithm for calculating

 *     the centroid as a weighted sum of the centroids

 *     of a decomposition of the area into (possibly overlapping) triangles.

 *     The algorithm has been extended to handle holes and multi-polygons.

 *     See http://www.faqs.org/faqs/graphics/algorithms-faq/

 *     for further details of the basic approach.

 * - **Dimension = 1** - Computes the average of the midpoints

 *     of all line segments weighted by the segment length.

 * - **Dimension = 0** - Compute the average coordinate over all points.

 *

 * If the input geometries are empty, a `null` Coordinate is returned.

 *

 */

class GEOS_DLL Centroid {

public:

    /** \brief

     * Computes the centroid point of a geometry.

     *

     * @param geom the geometry to use

     * @param cent will be set to the centroid point, if any

     *

     * @return `true` if a centroid could be computed,

     *         `false` otherwise (empty geom)

     */

    static bool getCentroid(const geom::Geometry& geom, geom::CoordinateXY& cent);

    /** \brief

     * Creates a new instance for computing the centroid of a geometry

     */

    Centroid(const geom::Geometry& geom)

        :

        areasum2(0.0),

        totalLength(0.0),

        ptCount(0)

    {

        add(geom);

    }

    /** \brief

     * Gets the computed centroid.

     *

     * @param cent will be set to the centroid point, if any

     *

     * @return `true` if a centroid could be computed,

     *         `false` otherwise (empty geom)

     */

    bool getCentroid(geom::CoordinateXY& cent) const;

private:

    std::unique_ptr<geom::CoordinateXY> areaBasePt;

    geom::CoordinateXY triangleCent3;

    geom::CoordinateXY cg3;

    geom::CoordinateXY lineCentSum;

    geom::CoordinateXY ptCentSum;

    double areasum2;

    double totalLength;

    int ptCount;

    /**

     * Adds a Geometry to the centroid total.

     *

     * @param geom the geometry to add

     */

    void add(const geom::Geometry& geom);

    void setAreaBasePoint(const geom::CoordinateXY& basePt);

    void add(const geom::Polygon& poly);

    void addShell(const geom::CoordinateSequence& pts);

    void addHole(const geom::CoordinateSequence& pts);

    void addTriangle(const geom::CoordinateXY& p0, const geom::CoordinateXY& p1, const geom::CoordinateXY& p2,

                     bool isPositiveArea);

    /**

     * Computes three times the centroid of the triangle p1-p2-p3.

     * The factor of 3 is

     * left in to permit division to be avoided until later.

     */

    static void centroid3(const geom::CoordinateXY& p1, const geom::CoordinateXY& p2, const geom::CoordinateXY& p3,

                          geom::CoordinateXY& c);

    /**

     * Returns twice the signed area of the triangle p1-p2-p3.

     * The area is positive if the triangle is oriented CCW, and negative if CW.

     */

    static double area2(const geom::CoordinateXY& p1, const geom::CoordinateXY& p2, const geom::CoordinateXY& p3);

    /**

     * Adds the line segments defined by an array of coordinates

     * to the linear centroid accumulators.

     *

     * @param pts an array of {@link Coordinate}s

     */

    void addLineSegments(const geom::CoordinateSequence& pts);

    /**

     * Adds a point to the point centroid accumulator.

     * @param pt a {@link Coordinate}

     */

    void addPoint(const geom::CoordinateXY& pt);

};

} // namespace geos::algorithm

} // namespace geos