osrm-backend/algorithms/route_name_extraction.hpp

/*

Copyright (c) 2015, Project OSRM contributors
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*/

#ifndef EXTRACT_ROUTE_NAMES_H
#define EXTRACT_ROUTE_NAMES_H

#include <boost/assert.hpp>

#include <algorithm>
#include <string>
#include <vector>

struct RouteNames
{
    std::string shortest_path_name_1;
    std::string shortest_path_name_2;
    std::string alternative_path_name_1;
    std::string alternative_path_name_2;
};

// construct routes names
template <class DataFacadeT, class SegmentT> struct ExtractRouteNames
{
  private:
    SegmentT PickNextLongestSegment(const std::vector<SegmentT> &segment_list,
                                    const unsigned blocked_name_id) const
    {
        SegmentT result_segment;
        result_segment.length = 0;

        for (const SegmentT &segment : segment_list)
        {
            if (segment.name_id != blocked_name_id && segment.length > result_segment.length &&
                segment.name_id != 0)
            {
                result_segment = segment;
            }
        }
        return result_segment;
    }

  public:
    RouteNames operator()(std::vector<SegmentT> &shortest_path_segments,
                          std::vector<SegmentT> &alternative_path_segments,
                          const DataFacadeT *facade) const
    {
        RouteNames route_names;

        SegmentT shortest_segment_1, shortest_segment_2;
        SegmentT alternative_segment_1, alternative_segment_2;

        auto length_comperator = [](const SegmentT &a, const SegmentT &b)
        {
            return a.length > b.length;
        };
        auto name_id_comperator = [](const SegmentT &a, const SegmentT &b)
        {
            return a.name_id < b.name_id;
        };

        if (shortest_path_segments.empty())
        {
            return route_names;
        }

        // pick the longest segment for the shortest path.
        tbb::parallel_sort(shortest_path_segments, length_comperator);
        shortest_segment_1 = shortest_path_segments[0];
        if (!alternative_path_segments.empty())
        {
            tbb::parallel_sort(alternative_path_segments, length_comperator);

            // also pick the longest segment for the alternative path
            alternative_segment_1 = alternative_path_segments[0];
        }

        // compute the set difference (for shortest path) depending on names between shortest and
        // alternative
        std::vector<SegmentT> shortest_path_set_difference(shortest_path_segments.size());
        tbb::parallel_sort(shortest_path_segments, name_id_comperator);
        tbb::parallel_sort(alternative_path_segments, name_id_comperator);
        std::set_difference(shortest_path_segments.begin(), shortest_path_segments.end(),
                            alternative_path_segments.begin(), alternative_path_segments.end(),
                            shortest_path_set_difference.begin(), name_id_comperator);

        tbb::parallel_sort(shortest_path_set_difference, length_comperator);
        shortest_segment_2 =
            PickNextLongestSegment(shortest_path_set_difference, shortest_segment_1.name_id);

        // compute the set difference (for alternative path) depending on names between shortest and
        // alternative
        // vectors are still sorted, no need to do again
        BOOST_ASSERT(std::is_sorted(shortest_path_segments.begin(), shortest_path_segments.end(),
                                    name_id_comperator));
        BOOST_ASSERT(std::is_sorted(alternative_path_segments.begin(),
                                    alternative_path_segments.end(), name_id_comperator));

        std::vector<SegmentT> alternative_path_set_difference(alternative_path_segments.size());
        std::set_difference(alternative_path_segments.begin(), alternative_path_segments.end(),
                            shortest_path_segments.begin(), shortest_path_segments.end(),
                            alternative_path_set_difference.begin(), name_id_comperator);

        tbb::parallel_sort(alternative_path_set_difference, length_comperator);

        if (!alternative_path_segments.empty())
        {
            alternative_segment_2 = PickNextLongestSegment(alternative_path_set_difference,
                                                           alternative_segment_1.name_id);
        }

        // move the segments into the order in which they occur.
        if (shortest_segment_1.position > shortest_segment_2.position)
        {
            std::swap(shortest_segment_1, shortest_segment_2);
        }
        if (alternative_segment_1.position > alternative_segment_2.position)
        {
            std::swap(alternative_segment_1, alternative_segment_2);
        }

        // fetching names for the selected segments
        route_names.shortest_path_name_1 = facade->get_name_for_id(shortest_segment_1.name_id);
        route_names.shortest_path_name_2 = facade->get_name_for_id(shortest_segment_2.name_id);

        route_names.alternative_path_name_1 =
            facade->get_name_for_id(alternative_segment_1.name_id);
        route_names.alternative_path_name_2 =
            facade->get_name_for_id(alternative_segment_2.name_id);

        return route_names;
    }
};

#endif // EXTRACT_ROUTE_NAMES_H