// Copyright (c) 2013-2015  The University of Western Sydney, Australia.
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org).
//
// $URL: https://github.com/CGAL/cgal/blob/v6.0.1/Cone_spanners_2/include/CGAL/Construct_yao_graph_2.h $
// $Id: include/CGAL/Construct_yao_graph_2.h 50cfbde3b84 $
// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-Commercial
//
//
// Authors: Weisheng Si, Quincy Tse, Frédérik Paradis

/*! \file Construct_yao_graph_2.h
 *
 * This header implements the functor for constructing Yao graphs.
 */

#ifndef CGAL_CONSTRUCT_YAO_GRAPH_2_H
#define CGAL_CONSTRUCT_YAO_GRAPH_2_H

#include <CGAL/license/Cone_spanners_2.h>


#include <iostream>
#include <cstdlib>
#include <utility>
#include <CGAL/Compute_cone_boundaries_2.h>
#include <CGAL/Cone_spanners_2/Less_by_direction_2.h>
#include <CGAL/Cone_spanners_enum_2.h>

#include <boost/config.hpp>
#include <boost/graph/adjacency_list.hpp>

namespace CGAL {

/*! \ingroup PkgConeSpanners2Ref

 \brief A template functor for constructing Yao graphs with a given set of 2D points and
         a given initial direction for the cone boundaries.

 \tparam Traits_  Must be either `CGAL::Exact_predicates_exact_constructions_kernel_with_root_of`
                  or `CGAL::Exact_predicates_inexact_constructions_kernel`.

 \tparam Graph_  The graph type to store the constructed cone based spanner.
                 It must be <A HREF="https://www.boost.org/libs/graph/doc/adjacency_list.html">`boost::adjacency_list`</A>
                 with `Traits_::Point_2` as `VertexProperties`
 */
template <typename Traits_, typename Graph_>
class Construct_yao_graph_2 {

public:
    /*! the geometric traits class. */
    typedef Traits_      Traits;
    /*! the specific type of `boost::adjacency_list`. */
    typedef Graph_                        Graph;

    /*! the point type */
    typedef typename Traits::Point_2                 Point_2;

    /*! the direction type */
    typedef typename Traits::Direction_2             Direction_2;

private:
    typedef typename Traits::Line_2                Line_2;
    typedef Less_by_direction_2<Traits, Graph_>    Less_by_direction;
    // a type for the set to store vertices sorted by a direction
    typedef std::set<typename Graph_::vertex_descriptor, Less_by_direction> Point_set;

    /* Store the number of cones.  */
    unsigned int  cone_number;

    /* Store whether even, odd or all cones are selected to construct graph. */
    Cones_selected cones_choice;

    /* Store the directions of the rays dividing the plane. The initial direction will be
       stored in rays[0].  */
    std::vector<Direction_2>   rays;

public:
    /*!
      \brief    Constructor.

      \param k     Number of cones to divide space into
      \param initial_direction  A direction denoting one of the rays dividing the
                   cones. This allows arbitrary rotations of the rays that divide
                   the plane.  (default: positive x-axis)
      \param cones_selected  Indicates whether even, odd or all cones are
                   selected to construct graph.
     */
    Construct_yao_graph_2 (unsigned int k,
                           Direction_2 initial_direction = Direction_2(1,0),
                           Cones_selected cones_selected = ALL_CONES
                          ): cone_number(k), cones_choice(cones_selected), rays(std::vector<Direction_2>(k))

    {
        if (k<2) {
            std::cout << "The number of cones must be larger than 1!" << std::endl;
            CGAL_assertion(false);
        }

        /* Initialize a functor, specialization will happen here depending on the kernel type to
         compute the cone boundaries either exactly or inexactly */
        Compute_cone_boundaries_2<Traits> compute_cones;
        // compute the rays using the functor
        compute_cones(k, initial_direction, rays.begin());
    }

    /*!
      \brief Function operator to construct a Yao graph.

      \details For the details of this algorithm, please refer to the User Manual.

      \tparam  PointInputIterator an `InputIterator` with value type `Point_2`.

      \param[in] start An iterator pointing to the first vertex of the input.
      \param[in]  end  An iterator pointing to the past-the-end location of the input.
      \param[out]  g   The constructed graph object.
     */
    template <typename PointInputIterator>
    Graph_& operator()(const PointInputIterator& start,
                       const PointInputIterator& end,
                       Graph_& g) {
        // add vertices into the graph
        for (PointInputIterator curr = start; curr != end; ++curr) {
            g[boost::add_vertex(g)] = *curr;
        }

        unsigned int i;   // ray index of the cw ray
        unsigned int j;   // index of the ccw ray

        // add edges into the graph for every cone
        int new_start = cones_choice != ALL_CONES ? cones_choice : 0;
        int increment = cones_choice != ALL_CONES ? 2 : 1;
        for (i = new_start; i < cone_number; i += increment) {
            j = (i+1) % cone_number;
            add_edges_in_cone(rays[i], rays[j], g);
        }

        return g;
    }

    /*! \brief returns the number of cones.
     */
    unsigned int number_of_cones() const {
        return cone_number;
    }

    /*! \brief outputs the set of directions to the iterator `result`.

      \tparam DirectionOutputIterator  an `OutputIterator` with value type `Direction_2`.
        \return `result`
    */
    template<class DirectionOutputIterator>
    DirectionOutputIterator directions(DirectionOutputIterator result) {
        typename std::vector<Direction_2>::iterator it;
        for (it=rays.begin(); it!=rays.end(); it++) {
            *result++ = *it;
        }
        return result;
    }

protected:

    /* Construct edges in one cone bounded by two directions.

     \param cwBound      The direction of the clockwise boundary of the cone.
     \param ccwBound     The direction of the counter-clockwise boundary.
     \param g            The Yao graph to be built.
    */
    void add_edges_in_cone(const Direction_2& cwBound, const Direction_2& ccwBound, Graph_& g) {
        if (ccwBound == cwBound) {
            // Degenerate case,  not allowed.
            throw std::out_of_range("The cw boundary and the ccw boundary shouldn't be same!");
        }

        // Ordering
        // here D1 is the reverse of D1 in the book, we find this is easier to implement
        const Less_by_direction  orderD1 (g, ccwBound);
        const Less_by_direction  orderD2 (g, cwBound);

        typename Graph_::vertex_iterator vit, ve;
        boost::tie(vit, ve) = boost::vertices(g);

        // Step 1: Sort S according to order induced by D1
        std::vector<typename Graph_::vertex_descriptor> S(vit, ve);
        std::sort(S.begin (), S.end (), orderD1);

        // Step 2: initialize an empty set to store vertices sorted by orderD2
        Point_set pst(orderD2);

        // Step 3: visit S in orderD1
        //         insert 'it' into pst
        //         search the min in pst
        for (typename std::vector<typename Graph_::vertex_descriptor>::const_iterator
                it = S.begin(); it != S.end(); ++it) {
            Less_euclidean_distance comp(g[*it], g);

            pst.insert(*it);
            // Find the last added node - O(logn)
            typename Point_set::iterator it2 = pst.find(*it);
            // Find minimum in pst from last ended node - O(n)
            typename Point_set::iterator min = std::min_element(++it2, pst.end(), comp);
            // add an edge
            if (min != pst.end()) {
                typename Graph_::edge_descriptor existing_e;
                bool                    existing;
                // check whether the edge already exists
                boost::tie(existing_e, existing)=boost::edge(*it, *min, g);
                if (!existing)
                    boost::add_edge(*it, *min, g);
            }

        } // end of for

    };     // end of add edges in cone


    /* Functor for comparing Euclidean distances of two vertices in a graph g to a given vertex.
      It is implemented by encapsulating the CGAL::has_smaller_distance_to_point() function.
     */
    struct Less_euclidean_distance {
        const Point_2& p;
        const Graph_& g;

        // constructor
        Less_euclidean_distance(const Point_2&p, const Graph_& g) : p(p), g(g) {}

        // operator
        bool operator() (const typename Point_set::iterator::value_type& i, const typename Point_set::iterator::value_type& j) {
            const Point_2& p1 = g[i];
            const Point_2& p2 = g[j];
            return has_smaller_distance_to_point(p, p1, p2);
        }
    };

};      // class Construct_yao_graph_2


}  // namespace CGAL


#endif
