osrm-backend/plugins/round_trip.hpp

/*

Copyright (c) 2015, Project OSRM contributors
All rights reserved.

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are permitted provided that the following conditions are met:

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list of conditions and the following disclaimer in the documentation and/or
other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
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WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
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(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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*/

#ifndef ROUND_TRIP_HPP
#define ROUND_TRIP_HPP

#include "plugin_base.hpp"

#include "../algorithms/object_encoder.hpp"
#include "../data_structures/query_edge.hpp"
#include "../data_structures/search_engine.hpp"
#include "../descriptors/descriptor_base.hpp"
#include "../descriptors/json_descriptor.hpp"
#include "../util/json_renderer.hpp"
#include "../util/make_unique.hpp"
#include "../util/string_util.hpp"
#include "../util/timing_util.hpp"
#include "../util/simple_logger.hpp"

#include <osrm/json_container.hpp>

#include <cstdlib>

#include <algorithm>
#include <memory>
#include <unordered_map>
#include <string>
#include <vector>
#include <limits> 

template <class DataFacadeT> class RoundTripPlugin final : public BasePlugin
{
  private:
    std::string descriptor_string;
    DataFacadeT *facade;
    std::unique_ptr<SearchEngine<DataFacadeT>> search_engine_ptr;

  public:
    explicit RoundTripPlugin(DataFacadeT *facade)
        : descriptor_string("trip"), facade(facade)
    {
        search_engine_ptr = osrm::make_unique<SearchEngine<DataFacadeT>>(facade);
    }

    const std::string GetDescriptor() const override final { return descriptor_string; }

    int HandleRequest(const RouteParameters &route_parameters,
                      osrm::json::Object &json_result) override final
    {
        // check if all inputs are coordinates
        if (!check_all_coordinates(route_parameters.coordinates))
        {
            return 400;
        }
        const bool checksum_OK = (route_parameters.check_sum == facade->GetCheckSum());

        // find phantom nodes for all input coords
        PhantomNodeArray phantom_node_vector(route_parameters.coordinates.size());
        for (const auto i : osrm::irange<std::size_t>(0, route_parameters.coordinates.size()))
        {
            // if client hints are helpful, encode hints
            if (checksum_OK && i < route_parameters.hints.size() &&
                !route_parameters.hints[i].empty())
            {
                PhantomNode current_phantom_node;
                ObjectEncoder::DecodeFromBase64(route_parameters.hints[i], current_phantom_node);
                if (current_phantom_node.is_valid(facade->GetNumberOfNodes()))
                {
                    phantom_node_vector[i].emplace_back(std::move(current_phantom_node));
                    continue;
                }
            }
            facade->IncrementalFindPhantomNodeForCoordinate(route_parameters.coordinates[i],
                                                            phantom_node_vector[i], 1);
            if (phantom_node_vector[i].size() > 1)
            {
                phantom_node_vector[i].erase(phantom_node_vector[i].begin());
            }
            BOOST_ASSERT(phantom_node_vector[i].front().is_valid(facade->GetNumberOfNodes()));
        }

        // compute the distance table of all phantom nodes
        std::shared_ptr<std::vector<EdgeWeight>> result_table =
            search_engine_ptr->distance_table(phantom_node_vector);

        if (!result_table)
        {
            return 400;
        }

        //////////////////////////////////////////////////////////////////////////////////////////////////
        // START GREEDY NEAREST NEIGHBOUR HERE
        // 1. grab a random location and mark as starting point
        // 2. find the nearest unvisited neighbour, set it as the current location and mark as visited
        // 3. repeat 2 until there is no unvisited location
        // 4. return route back to starting point
        // 5. compute route
        // 6. repeat 1-5 with different starting points and choose iteration with shortest trip
        // 6. DONE!
        //////////////////////////////////////////////////////////////////////////////////////////////////

        const auto number_of_locations = phantom_node_vector.size();
        // min_route is the shortest route found
        InternalRouteResult min_route;
        min_route.shortest_path_length = std::numeric_limits<int>::max();
        // min_loc_permutation stores the order of visited locations of the shortest route
        std::vector<int> min_loc_permutation;

        // is_lonely_island[i] indicates whether node i is a node that cannot be reached from other nodes
        //  1 means that node i is a lonely island
        //  0 means that it is not known for node i
        // -1 means that node i is not a lonely island but a reachable, connected node
        std::vector<int> is_lonely_island(number_of_locations, 0);
        int count_unreachables;

        // ALWAYS START AT ANOTHER STARTING POINT
        for(int start_node = 0; start_node < number_of_locations; ++start_node)
        {
        
            if (is_lonely_island[start_node] >= 0)
            {
                // if node is a lonely island it is an unsuitable node to start from and shall be skipped
                if (is_lonely_island[start_node])
                    continue;
                count_unreachables = 0;
                auto start_dist_begin = result_table->begin() + (start_node * number_of_locations);
                auto start_dist_end = result_table->begin() + ((start_node + 1) * number_of_locations);
                for (auto it2 = start_dist_begin; it2 != start_dist_end; ++it2) {
                    if (*it2 == 0 || *it2 == std::numeric_limits<int>::max()) {
                        ++count_unreachables;
                    }
                }
                if (count_unreachables >= number_of_locations) {
                    is_lonely_island[start_node] = 1;
                    continue;
                }
            }

            int curr_node = start_node;   
            is_lonely_island[curr_node] = -1;
            InternalRouteResult raw_route;
            //TODO: Should we always use the same vector or does it not matter at all because of loop scope?
            std::vector<int> loc_permutation(number_of_locations, -1);
            loc_permutation[start_node] = 0;
            // visited[i] indicates whether node i was already visited by the salesman
            std::vector<bool> visited(number_of_locations, false);
            visited[start_node] = true;

            PhantomNodes viapoint;
            // 3. REPEAT FOR EVERY UNVISITED NODE
            for(int via_point = 1; via_point < number_of_locations; ++via_point)
            {
                int min_dist = std::numeric_limits<int>::max();
                int min_id = -1;

                // 2. FIND NEAREST NEIGHBOUR
                auto row_begin_iterator = result_table->begin() + (curr_node * number_of_locations);
                auto row_end_iterator = result_table->begin() + ((curr_node + 1) * number_of_locations);
                for (auto it = row_begin_iterator; it != row_end_iterator; ++it) {
                    auto index = std::distance(row_begin_iterator, it); 
                    if (is_lonely_island[index] < 1 && !visited[index] && *it < min_dist)
                    {
                        min_dist = *it;
                        min_id = index;
                    }
                }
                // in case there was no unvisited and reachable node found, it means that all remaining (unvisited) nodes must be lonely islands
                if (min_id == -1)
                {
                    for(int loc = 0; loc < visited.size(); ++loc) {
                        if (!visited[loc]) {
                            is_lonely_island[loc] = 1;
                        }
                    }
                    break;
                }
                // set the nearest unvisited location as the next via_point
                else
                {
                    is_lonely_island[min_id] = -1;
                    loc_permutation[min_id] = via_point;
                    visited[min_id] = true;
                    viapoint = PhantomNodes{phantom_node_vector[curr_node][0], phantom_node_vector[min_id][0]};
                    raw_route.segment_end_coordinates.emplace_back(viapoint);
                    curr_node = min_id;
                }
            }

            // 4. ROUTE BACK TO STARTING POINT
            viapoint = PhantomNodes{raw_route.segment_end_coordinates.back().target_phantom, phantom_node_vector[start_node][0]};
            raw_route.segment_end_coordinates.emplace_back(viapoint);

            // 5. COMPUTE ROUTE
            search_engine_ptr->shortest_path(raw_route.segment_end_coordinates, route_parameters.uturns, raw_route);
            // SimpleLogger().Write() << "Route starting at " << start_node << " with length " << raw_route.shortest_path_length;
            
            // check round trip with this starting point is shorter than the shortest round trip found till now
            if (raw_route.shortest_path_length < min_route.shortest_path_length) {
                min_route = raw_route;
                min_loc_permutation = loc_permutation;
            }
        }

        SimpleLogger().Write() << "Shortest route " << min_route.shortest_path_length;

        // return result to json
        std::unique_ptr<BaseDescriptor<DataFacadeT>> descriptor;
        descriptor = osrm::make_unique<JSONDescriptor<DataFacadeT>>(facade);
        
        descriptor->SetConfig(route_parameters);
        descriptor->Run(min_route, json_result);

        osrm::json::Array json_loc_permutation;
        json_loc_permutation.values.insert(json_loc_permutation.values.end(), min_loc_permutation.begin(), min_loc_permutation.end());
        json_result.values["loc_permutation"] = json_loc_permutation;

        return 200;
    }

};

#endif // ROUND_TRIP_HPP