osrm-backend/include/engine/plugins/trip.hpp

#ifndef TRIP_HPP
#define TRIP_HPP

#include "engine/plugins/plugin_base.hpp"

#include "engine/object_encoder.hpp"
#include "extractor/tarjan_scc.hpp"
#include "engine/trip/trip_nearest_neighbour.hpp"
#include "engine/trip/trip_farthest_insertion.hpp"
#include "engine/trip/trip_brute_force.hpp"
#include "engine/search_engine.hpp"
#include "util/matrix_graph_wrapper.hpp" // wrapper to use tarjan scc on dist table
#include "engine/api_response_generator.hpp"
#include "util/make_unique.hpp"
#include "util/dist_table_wrapper.hpp" // to access the dist table more easily
#include "osrm/json_container.hpp"

#include <boost/assert.hpp>

#include <cstdlib>
#include <algorithm>
#include <memory>
#include <string>
#include <utility>
#include <vector>
#include <iterator>

namespace osrm
{
namespace engine
{
namespace plugins
{

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

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

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

    std::vector<PhantomNode> GetPhantomNodes(const RouteParameters &route_parameters)
    {
        const bool checksum_OK = (route_parameters.check_sum == facade->GetCheckSum());
        const auto &input_bearings = route_parameters.bearings;

        std::vector<PhantomNode> phantom_node_list;
        phantom_node_list.reserve(route_parameters.coordinates.size());

        // find phantom nodes for all input coords
        for (const auto i : util::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())
            {
                auto current_phantom_node = decodeBase64<PhantomNode>(route_parameters.hints[i]);
                if (current_phantom_node.IsValid(facade->GetNumberOfNodes()))
                {
                    phantom_node_list.push_back(std::move(current_phantom_node));
                    continue;
                }
            }
            const int bearing = input_bearings.size() > 0 ? input_bearings[i].first : 0;
            const int range = input_bearings.size() > 0
                                  ? (input_bearings[i].second ? *input_bearings[i].second : 10)
                                  : 180;
            auto results =
                facade->NearestPhantomNodes(route_parameters.coordinates[i], 1, bearing, range);
            if (results.empty())
            {
                break;
            }
            phantom_node_list.push_back(std::move(results.front().phantom_node));
            BOOST_ASSERT(phantom_node_list.back().IsValid(facade->GetNumberOfNodes()));
        }

        return phantom_node_list;
    }

    // Object to hold all strongly connected components (scc) of a graph
    // to access all graphs with component ID i, get the iterators by:
    // auto start = std::begin(scc_component.component) + scc_component.range[i];
    // auto end = std::begin(scc_component.component) + scc_component.range[i+1];
    struct SCC_Component
    {
        // in_component: all NodeIDs sorted by component ID
        // in_range: index where a new component starts
        //
        // example: NodeID 0, 1, 2, 4, 5 are in component 0
        //          NodeID 3, 6, 7, 8    are in component 1
        //          => in_component = [0, 1, 2, 4, 5, 3, 6, 7, 8]
        //          => in_range = [0, 5]
        SCC_Component(std::vector<NodeID> in_component_nodes, std::vector<size_t> in_range)
            : component(std::move(in_component_nodes)), range(std::move(in_range))
        {
            BOOST_ASSERT_MSG(component.size() > 0, "there's no scc component");
            BOOST_ASSERT_MSG(*std::max_element(range.begin(), range.end()) == component.size(),
                             "scc component ranges are out of bound");
            BOOST_ASSERT_MSG(*std::min_element(range.begin(), range.end()) == 0,
                             "invalid scc component range");
            BOOST_ASSERT_MSG(std::is_sorted(std::begin(range), std::end(range)),
                             "invalid component ranges");
        };

        std::size_t GetNumberOfComponents() const
        {
            BOOST_ASSERT_MSG(range.size() > 0, "there's no range");
            return range.size() - 1;
        }

        const std::vector<NodeID> component;
        std::vector<std::size_t> range;
    };

    // takes the number of locations and its distance matrix,
    // identifies and splits the graph in its strongly connected components (scc)
    // and returns an SCC_Component
    SCC_Component SplitUnaccessibleLocations(const std::size_t number_of_locations,
                                             const util::DistTableWrapper<EdgeWeight> &result_table)
    {

        if (std::find(std::begin(result_table), std::end(result_table), INVALID_EDGE_WEIGHT) ==
            std::end(result_table))
        {
            // whole graph is one scc
            std::vector<NodeID> location_ids(number_of_locations);
            std::iota(std::begin(location_ids), std::end(location_ids), 0);
            std::vector<size_t> range = {0, location_ids.size()};
            return SCC_Component(std::move(location_ids), std::move(range));
        }

        // Run TarjanSCC
        auto wrapper = std::make_shared<util::MatrixGraphWrapper<EdgeWeight>>(
            result_table.GetTable(), number_of_locations);
        auto scc = extractor::TarjanSCC<util::MatrixGraphWrapper<EdgeWeight>>(wrapper);
        scc.run();

        const auto number_of_components = scc.get_number_of_components();

        std::vector<std::size_t> range_insertion;
        std::vector<std::size_t> range;
        range_insertion.reserve(number_of_components);
        range.reserve(number_of_components);

        std::vector<NodeID> components(number_of_locations, 0);

        std::size_t prefix = 0;
        for (std::size_t j = 0; j < number_of_components; ++j)
        {
            range_insertion.push_back(prefix);
            range.push_back(prefix);
            prefix += scc.get_component_size(j);
        }
        // senitel
        range.push_back(components.size());

        for (std::size_t i = 0; i < number_of_locations; ++i)
        {
            components[range_insertion[scc.get_component_id(i)]] = i;
            ++range_insertion[scc.get_component_id(i)];
        }

        return SCC_Component(std::move(components), std::move(range));
    }

    void SetLocPermutationOutput(const std::vector<NodeID> &permutation,
                                 util::json::Object &json_result)
    {
        util::json::Array json_permutation;
        json_permutation.values.insert(std::end(json_permutation.values), std::begin(permutation),
                                       std::end(permutation));
        json_result.values["permutation"] = json_permutation;
    }

    InternalRouteResult ComputeRoute(const std::vector<PhantomNode> &phantom_node_list,
                                     const RouteParameters &route_parameters,
                                     const std::vector<NodeID> &trip)
    {
        InternalRouteResult min_route;
        // given he final trip, compute total distance and return the route and location permutation
        PhantomNodes viapoint;
        const auto start = std::begin(trip);
        const auto end = std::end(trip);
        // computes a roundtrip from the nodes in trip
        for (auto it = start; it != end; ++it)
        {
            const auto from_node = *it;
            // if from_node is the last node, compute the route from the last to the first location
            const auto to_node = std::next(it) != end ? *std::next(it) : *start;

            viapoint = PhantomNodes{phantom_node_list[from_node], phantom_node_list[to_node]};
            min_route.segment_end_coordinates.emplace_back(viapoint);
        }
        BOOST_ASSERT(min_route.segment_end_coordinates.size() == trip.size());

        std::vector<bool> uturns(trip.size() + 1);
        BOOST_ASSERT(route_parameters.uturns.size() > 0);
        std::transform(trip.begin(), trip.end(), uturns.begin(),
                       [&route_parameters](const NodeID idx)
                       {
                           return route_parameters.uturns[idx];
                       });
        BOOST_ASSERT(uturns.size() > 0);
        uturns.back() = route_parameters.uturns[trip.front()];

        search_engine_ptr->shortest_path(min_route.segment_end_coordinates, uturns, min_route);

        BOOST_ASSERT_MSG(min_route.shortest_path_length < INVALID_EDGE_WEIGHT, "unroutable route");
        return min_route;
    }

    Status HandleRequest(const RouteParameters &route_parameters,
                         util::json::Object &json_result) override final
    {
        if (max_locations_trip > 0 &&
            (static_cast<int>(route_parameters.coordinates.size()) > max_locations_trip))
        {
            json_result.values["status_message"] =
                "Number of entries " + std::to_string(route_parameters.coordinates.size()) +
                " is higher than current maximum (" + std::to_string(max_locations_trip) + ")";
            return Status::Error;
        }

        // check if all inputs are coordinates
        if (!check_all_coordinates(route_parameters.coordinates))
        {
            json_result.values["status_message"] = "Invalid coordinates";
            return Status::Error;
        }

        const auto &input_bearings = route_parameters.bearings;
        if (input_bearings.size() > 0 &&
            route_parameters.coordinates.size() != input_bearings.size())
        {
            json_result.values["status_message"] =
                "Number of bearings does not match number of coordinates";
            return Status::Error;
        }

        // get phantom nodes
        auto phantom_node_list = GetPhantomNodes(route_parameters);
        if (phantom_node_list.size() != route_parameters.coordinates.size())
        {
            BOOST_ASSERT(phantom_node_list.size() < route_parameters.coordinates.size());
            json_result.values["status_message"] =
                std::string("Could not find a matching segment for coordinate ") +
                std::to_string(phantom_node_list.size());
            return Status::NoSegment;
        }

        const auto number_of_locations = phantom_node_list.size();

        // compute the distance table of all phantom nodes
        const auto result_table = util::DistTableWrapper<EdgeWeight>(
            *search_engine_ptr->distance_table(phantom_node_list, phantom_node_list),
            number_of_locations);

        if (result_table.size() == 0)
        {
            return Status::Error;
        }

        const constexpr std::size_t BF_MAX_FEASABLE = 10;
        BOOST_ASSERT_MSG(result_table.size() == number_of_locations * number_of_locations,
                         "Distance Table has wrong size");

        // get scc components
        SCC_Component scc = SplitUnaccessibleLocations(number_of_locations, result_table);

        using NodeIDIterator = typename std::vector<NodeID>::const_iterator;

        std::vector<std::vector<NodeID>> route_result;
        route_result.reserve(scc.GetNumberOfComponents());
        // run Trip computation for every SCC
        for (std::size_t k = 0; k < scc.GetNumberOfComponents(); ++k)
        {
            const auto component_size = scc.range[k + 1] - scc.range[k];

            BOOST_ASSERT_MSG(component_size > 0, "invalid component size");

            std::vector<NodeID> scc_route;
            NodeIDIterator start = std::begin(scc.component) + scc.range[k];
            NodeIDIterator end = std::begin(scc.component) + scc.range[k + 1];

            if (component_size > 1)
            {

                if (component_size < BF_MAX_FEASABLE)
                {
                    scc_route = trip::BruteForceTrip(start, end, number_of_locations, result_table);
                }
                else
                {
                    scc_route =
                        trip::FarthestInsertionTrip(start, end, number_of_locations, result_table);
                }

                // use this output if debugging of route is needed:
                // util::SimpleLogger().Write() << "Route #" << k << ": " << [&scc_route]()
                // {
                //     std::string s = "";
                //     for (auto x : scc_route)
                //     {
                //         s += std::to_string(x) + " ";
                //     }
                //     return s;
                // }();
            }
            else
            {
                scc_route = std::vector<NodeID>(start, end);
            }

            route_result.push_back(std::move(scc_route));
        }

        // compute all round trip routes
        std::vector<InternalRouteResult> comp_route;
        comp_route.reserve(route_result.size());
        for (auto &elem : route_result)
        {
            comp_route.push_back(ComputeRoute(phantom_node_list, route_parameters, elem));
        }

        // prepare JSON output
        // create a json object for every trip
        util::json::Array trip;
        for (std::size_t i = 0; i < route_result.size(); ++i)
        {
            util::json::Object scc_trip;

            // annotate comp_route[i] as a json trip
            auto generator = MakeApiResponseGenerator(facade);
            generator.DescribeRoute(route_parameters, comp_route[i], scc_trip);

            // set permutation output
            SetLocPermutationOutput(route_result[i], scc_trip);
            // set viaroute output
            trip.values.push_back(std::move(scc_trip));
        }

        if (trip.values.empty())
        {
            json_result.values["status_message"] = "Cannot find trips";
            return Status::EmptyResult;
        }

        json_result.values["trips"] = std::move(trip);
        json_result.values["status_message"] = "Found trips";
        return Status::Ok;
    }
};
}
}
}

#endif // TRIP_HPP