#ifndef OSRM_ENGINE_ROUTING_BASE_CH_HPP
#define OSRM_ENGINE_ROUTING_BASE_CH_HPP

#include "engine/algorithm.hpp"
#include "engine/datafacade.hpp"
#include "engine/routing_algorithms/routing_base.hpp"
#include "engine/search_engine_data.hpp"

#include "util/typedefs.hpp"

#include <boost/assert.hpp>

namespace osrm::engine::routing_algorithms::ch
{

// Stalling
template <bool DIRECTION, typename HeapT>
bool stallAtNode(const DataFacade<Algorithm> &facade,
                 const typename HeapT::HeapNode &heapNode,
                 const HeapT &query_heap)
{
    for (auto edge : facade.GetAdjacentEdgeRange(heapNode.node))
    {
        const auto &data = facade.GetEdgeData(edge);
        if (DIRECTION == REVERSE_DIRECTION ? data.forward : data.backward)
        {
            const NodeID to = facade.GetTarget(edge);
            const EdgeWeight edge_weight = data.weight;
            BOOST_ASSERT_MSG(edge_weight > EdgeWeight{0}, "edge_weight invalid");
            const auto toHeapNode = query_heap.GetHeapNodeIfWasInserted(to);
            if (toHeapNode)
            {
                if (toHeapNode->weight + edge_weight < heapNode.weight)
                {
                    return true;
                }
            }
        }
    }
    return false;
}

template <bool DIRECTION>
void relaxOutgoingEdges(const DataFacade<Algorithm> &facade,
                        const SearchEngineData<Algorithm>::QueryHeap::HeapNode &heapNode,
                        SearchEngineData<Algorithm>::QueryHeap &heap)
{
    for (const auto edge : facade.GetAdjacentEdgeRange(heapNode.node))
    {
        const auto &data = facade.GetEdgeData(edge);
        if (DIRECTION == FORWARD_DIRECTION ? data.forward : data.backward)
        {
            const NodeID to = facade.GetTarget(edge);
            const EdgeWeight edge_weight = data.weight;

            BOOST_ASSERT_MSG(edge_weight > EdgeWeight{0}, "edge_weight invalid");
            const EdgeWeight to_weight = heapNode.weight + edge_weight;

            const auto toHeapNode = heap.GetHeapNodeIfWasInserted(to);
            // New Node discovered -> Add to Heap + Node Info Storage
            if (!toHeapNode)
            {
                heap.Insert(to, to_weight, heapNode.node);
            }
            // Found a shorter Path -> Update weight
            else if (to_weight < toHeapNode->weight)
            {
                // new parent
                toHeapNode->data.parent = heapNode.node;
                toHeapNode->weight = to_weight;
                heap.DecreaseKey(*toHeapNode);
            }
        }
    }
}

/*
min_edge_offset is needed in case we use multiple
nodes as start/target nodes with different (even negative) offsets.
In that case the termination criterion is not correct
anymore.

Example:
forward heap: a(-100), b(0),
reverse heap: c(0), d(100)

a --- d
  \ /
  / \
b --- c

This is equivalent to running a bi-directional Dijkstra on the following graph:

    a --- d
   /  \ /  \
  y    x    z
   \  / \  /
    b --- c

The graph is constructed by inserting nodes y and z that are connected to the initial nodes
using edges (y, a) with weight -100, (y, b) with weight 0 and,
(d, z) with weight 100, (c, z) with weight 0 corresponding.
Since we are dealing with a graph that contains _negative_ edges,
we need to add an offset to the termination criterion.
*/
static constexpr bool ENABLE_STALLING = true;
static constexpr bool DISABLE_STALLING = false;
template <bool DIRECTION, bool STALLING = ENABLE_STALLING>
void routingStep(const DataFacade<Algorithm> &facade,
                 SearchEngineData<Algorithm>::QueryHeap &forward_heap,
                 SearchEngineData<Algorithm>::QueryHeap &reverse_heap,
                 NodeID &middle_node_id,
                 EdgeWeight &upper_bound,
                 EdgeWeight min_edge_offset,
                 const std::vector<NodeID> &force_step_nodes)
{
    auto heapNode = forward_heap.DeleteMinGetHeapNode();
    const auto reverseHeapNode = reverse_heap.GetHeapNodeIfWasInserted(heapNode.node);

    if (reverseHeapNode)
    {
        const EdgeWeight new_weight = reverseHeapNode->weight + heapNode.weight;
        if (new_weight < upper_bound)
        {
            if (shouldForceStep(force_step_nodes, heapNode, *reverseHeapNode) ||
                // in this case we are looking at a bi-directional way where the source
                // and target phantom are on the same edge based node
                new_weight < EdgeWeight{0})
            {
                // Before forcing step, check whether there is a loop present at the node.
                // We may find a valid weight path by following the loop.
                for (const auto edge : facade.GetAdjacentEdgeRange(heapNode.node))
                {
                    const auto &data = facade.GetEdgeData(edge);
                    if (DIRECTION == FORWARD_DIRECTION ? data.forward : data.backward)
                    {
                        const NodeID to = facade.GetTarget(edge);
                        if (to == heapNode.node)
                        {
                            const EdgeWeight edge_weight = data.weight;
                            const EdgeWeight loop_weight = new_weight + edge_weight;
                            if (loop_weight >= EdgeWeight{0} && loop_weight < upper_bound)
                            {
                                middle_node_id = heapNode.node;
                                upper_bound = loop_weight;
                            }
                        }
                    }
                }
            }
            else
            {
                BOOST_ASSERT(new_weight >= EdgeWeight{0});

                middle_node_id = heapNode.node;
                upper_bound = new_weight;
            }
        }
    }

    // make sure we don't terminate too early if we initialize the weight
    // for the nodes in the forward heap with the forward/reverse offset
    BOOST_ASSERT(min_edge_offset <= EdgeWeight{0});
    if (heapNode.weight + min_edge_offset > upper_bound)
    {
        forward_heap.DeleteAll();
        return;
    }

    // Stalling
    if (STALLING && stallAtNode<DIRECTION>(facade, heapNode, forward_heap))
    {
        return;
    }

    relaxOutgoingEdges<DIRECTION>(facade, heapNode, forward_heap);
}

/**
 * Given a sequence of connected `NodeID`s in the CH graph, performs a depth-first unpacking of
 * the shortcut
 * edges.  For every "original" edge found, it calls the `callback` with the two NodeIDs for the
 * edge, and the EdgeData
 * for that edge.
 *
 * The primary purpose of this unpacking is to expand a path through the CH into the original
 * route through the
 * pre-contracted graph.
 *
 * Because of the depth-first-search, the `callback` will effectively be called in sequence for
 * the original route
 * from beginning to end.
 *
 * @param packed_path_begin iterator pointing to the start of the NodeID list
 * @param packed_path_end iterator pointing to the end of the NodeID list
 * @param callback void(NodeID first, NodeID second, const EdgeID &) called for each
 * original edge found.
 */
template <typename BidirectionalIterator, typename Callback>
void unpackPath(const DataFacade<Algorithm> &facade,
                BidirectionalIterator packed_path_begin,
                BidirectionalIterator packed_path_end,
                Callback &&callback)
{
    // make sure we have at least something to unpack
    if (packed_path_begin == packed_path_end)
        return;

    std::stack<std::pair<NodeID, NodeID>> recursion_stack;

    // We have to push the path in reverse order onto the stack because it's LIFO.
    for (auto current = std::prev(packed_path_end); current != packed_path_begin;
         current = std::prev(current))
    {
        recursion_stack.emplace(*std::prev(current), *current);
    }

    std::pair<NodeID, NodeID> edge;
    while (!recursion_stack.empty())
    {
        edge = recursion_stack.top();
        recursion_stack.pop();

        // Look for an edge on the forward CH graph (.forward)
        EdgeID smaller_edge_id = facade.FindSmallestEdge(
            edge.first, edge.second, [](const auto &data) { return data.forward; });

        // If we didn't find one there, the we might be looking at a part of the path that
        // was found using the backward search.  Here, we flip the node order (.second, .first)
        // and only consider edges with the `.backward` flag.
        if (SPECIAL_EDGEID == smaller_edge_id)
        {
            smaller_edge_id = facade.FindSmallestEdge(
                edge.second, edge.first, [](const auto &data) { return data.backward; });
        }

        // If we didn't find anything *still*, then something is broken and someone has
        // called this function with bad values.
        BOOST_ASSERT_MSG(smaller_edge_id != SPECIAL_EDGEID, "Invalid smaller edge ID");

        const auto &data = facade.GetEdgeData(smaller_edge_id);
        BOOST_ASSERT_MSG(data.weight != std::numeric_limits<EdgeWeight>::max(),
                         "edge weight invalid");

        // If the edge is a shortcut, we need to add the two halfs to the stack.
        if (data.shortcut)
        { // unpack
            const NodeID middle_node_id = data.turn_id;
            // Note the order here - we're adding these to a stack, so we
            // want the first->middle to get visited before middle->second
            recursion_stack.emplace(middle_node_id, edge.second);
            recursion_stack.emplace(edge.first, middle_node_id);
        }
        else
        {
            // We found an original edge, call our callback.
            callback(edge.first, edge.second, smaller_edge_id);
        }
    }
}

template <typename BidirectionalIterator>
EdgeDistance calculateEBGNodeAnnotations(const DataFacade<Algorithm> &facade,
                                         BidirectionalIterator packed_path_begin,
                                         BidirectionalIterator packed_path_end)
{
    // Make sure we have at least something to unpack
    if (packed_path_begin == packed_path_end ||
        std::distance(packed_path_begin, packed_path_end) <= 1)
        return {0};

    std::stack<std::tuple<NodeID, NodeID, bool>> recursion_stack;
    std::stack<EdgeDistance> distance_stack;
    // We have to push the path in reverse order onto the stack because it's LIFO.
    for (auto current = std::prev(packed_path_end); current > packed_path_begin;
         current = std::prev(current))
    {
        recursion_stack.emplace(*std::prev(current), *current, false);
    }

    std::tuple<NodeID, NodeID, bool> edge;
    while (!recursion_stack.empty())
    {
        edge = recursion_stack.top();
        recursion_stack.pop();

        // Have we processed the edge before? tells us if we have values in the durations stack that
        // we can add up
        if (!std::get<2>(edge))
        { // haven't processed edge before, so process it in the body!

            std::get<2>(edge) = true; // mark that this edge will now be processed

            // Look for an edge on the forward CH graph (.forward)
            EdgeID smaller_edge_id =
                facade.FindSmallestEdge(std::get<0>(edge),
                                        std::get<1>(edge),
                                        [](const auto &data) { return data.forward; });

            // If we didn't find one there, the we might be looking at a part of the path that
            // was found using the backward search.  Here, we flip the node order (.second,
            // .first) and only consider edges with the `.backward` flag.
            if (SPECIAL_EDGEID == smaller_edge_id)
            {
                smaller_edge_id =
                    facade.FindSmallestEdge(std::get<1>(edge),
                                            std::get<0>(edge),
                                            [](const auto &data) { return data.backward; });
            }

            // If we didn't find anything *still*, then something is broken and someone has
            // called this function with bad values.
            BOOST_ASSERT_MSG(smaller_edge_id != SPECIAL_EDGEID, "Invalid smaller edge ID");

            const auto &data = facade.GetEdgeData(smaller_edge_id);
            BOOST_ASSERT_MSG(data.weight != std::numeric_limits<EdgeWeight>::max(),
                             "edge weight invalid");

            // If the edge is a shortcut, we need to add the two halfs to the stack.
            if (data.shortcut)
            { // unpack
                const NodeID middle_node_id = data.turn_id;
                // Note the order here - we're adding these to a stack, so we
                // want the first->middle to get visited before middle->second
                recursion_stack.emplace(edge);
                recursion_stack.emplace(middle_node_id, std::get<1>(edge), false);
                recursion_stack.emplace(std::get<0>(edge), middle_node_id, false);
            }
            else
            {
                // compute the duration here and put it onto the duration stack using method
                // similar to annotatePath but smaller
                EdgeDistance distance = computeEdgeDistance(facade, std::get<0>(edge));
                distance_stack.emplace(distance);
            }
        }
        else
        { // the edge has already been processed. this means that there are enough values in the
            // distances stack

            BOOST_ASSERT_MSG(distance_stack.size() >= 2,
                             "There are not enough (at least 2) values on the distance stack");
            EdgeDistance distance1 = distance_stack.top();
            distance_stack.pop();
            EdgeDistance distance2 = distance_stack.top();
            distance_stack.pop();
            EdgeDistance distance = distance1 + distance2;
            distance_stack.emplace(distance);
        }
    }

    EdgeDistance total_distance = {0};
    while (!distance_stack.empty())
    {
        total_distance += distance_stack.top();
        distance_stack.pop();
    }

    return total_distance;
}

template <typename RandomIter, typename FacadeT>
void unpackPath(const FacadeT &facade,
                RandomIter packed_path_begin,
                RandomIter packed_path_end,
                const PhantomEndpoints &route_endpoints,
                std::vector<PathData> &unpacked_path)
{
    const auto nodes_number = std::distance(packed_path_begin, packed_path_end);
    BOOST_ASSERT(nodes_number > 0);

    std::vector<NodeID> unpacked_nodes;
    std::vector<EdgeID> unpacked_edges;
    unpacked_nodes.reserve(nodes_number);
    unpacked_edges.reserve(nodes_number);

    unpacked_nodes.push_back(*packed_path_begin);
    if (nodes_number > 1)
    {
        unpackPath(facade,
                   packed_path_begin,
                   packed_path_end,
                   [&]([[maybe_unused]] NodeID first, NodeID second, const auto &edge_id)
                   {
                       BOOST_ASSERT(first == unpacked_nodes.back());
                       unpacked_nodes.push_back(second);
                       unpacked_edges.push_back(edge_id);
                   });
    }

    annotatePath(facade, route_endpoints, unpacked_nodes, unpacked_edges, unpacked_path);
}

/**
 * Unpacks a single edge (NodeID->NodeID) from the CH graph down to it's original non-shortcut
 * route.
 * @param from the node the CH edge starts at
 * @param to the node the CH edge finishes at
 * @param unpacked_path the sequence of original NodeIDs that make up the expanded CH edge
 */
void unpackEdge(const DataFacade<Algorithm> &facade,
                const NodeID from,
                const NodeID to,
                std::vector<NodeID> &unpacked_path);

void retrievePackedPathFromHeap(const SearchEngineData<Algorithm>::QueryHeap &forward_heap,
                                const SearchEngineData<Algorithm>::QueryHeap &reverse_heap,
                                const NodeID middle_node_id,
                                std::vector<NodeID> &packed_path);

void retrievePackedPathFromSingleHeap(const SearchEngineData<Algorithm>::QueryHeap &search_heap,
                                      const NodeID middle_node_id,
                                      std::vector<NodeID> &packed_path);

void retrievePackedPathFromSingleManyToManyHeap(
    const SearchEngineData<Algorithm>::ManyToManyQueryHeap &search_heap,
    const NodeID middle_node_id,
    std::vector<NodeID> &packed_path);

// assumes that heaps are already setup correctly.
// ATTENTION: This only works if no additional offset is supplied next to the Phantom Node
// Offsets.
// In case additional offsets are supplied, you might have to force a routing step first.
// A forced step might be necessary, if source and target are on the same segment.
// If this is the case and the offsets of the respective direction are larger for the source
// than the target
// then a force step is required (e.g. source_phantom.forward_segment_id ==
// target_phantom.forward_segment_id
// && source_phantom.GetForwardWeightPlusOffset() > target_phantom.GetForwardWeightPlusOffset())
// requires
// a force step, if the heaps have been initialized with positive offsets.
void search(SearchEngineData<Algorithm> &engine_working_data,
            const DataFacade<Algorithm> &facade,
            SearchEngineData<Algorithm>::QueryHeap &forward_heap,
            SearchEngineData<Algorithm>::QueryHeap &reverse_heap,
            EdgeWeight &weight,
            std::vector<NodeID> &packed_leg,
            const std::vector<NodeID> &force_step_nodes,
            const EdgeWeight duration_upper_bound = INVALID_EDGE_WEIGHT);

template <typename PhantomEndpointT>
void search(SearchEngineData<Algorithm> &engine_working_data,
            const DataFacade<Algorithm> &facade,
            SearchEngineData<Algorithm>::QueryHeap &forward_heap,
            SearchEngineData<Algorithm>::QueryHeap &reverse_heap,
            EdgeWeight &weight,
            std::vector<NodeID> &packed_leg,
            const std::vector<NodeID> &force_step_nodes,
            const PhantomEndpointT & /*endpoints*/,
            const EdgeWeight duration_upper_bound = INVALID_EDGE_WEIGHT)
{
    // Avoid templating the CH search implementations.
    return search(engine_working_data,
                  facade,
                  forward_heap,
                  reverse_heap,
                  weight,
                  packed_leg,
                  force_step_nodes,
                  duration_upper_bound);
}

// Requires the heaps for be empty
// If heaps should be adjusted to be initialized outside of this function,
// the addition of force_step parameters might be required
double getNetworkDistance(SearchEngineData<Algorithm> &engine_working_data,
                          const DataFacade<ch::Algorithm> &facade,
                          SearchEngineData<Algorithm>::QueryHeap &forward_heap,
                          SearchEngineData<Algorithm>::QueryHeap &reverse_heap,
                          const PhantomNode &source_phantom,
                          const PhantomNode &target_phantom,
                          EdgeWeight duration_upper_bound = INVALID_EDGE_WEIGHT);

template <typename EdgeMetric>
std::tuple<EdgeMetric, EdgeDistance> getLoopMetric(const DataFacade<Algorithm> &facade, NodeID node)
{
    EdgeMetric loop_metric;
    if constexpr (std::is_same<EdgeMetric, EdgeDuration>::value)
    {
        loop_metric = INVALID_EDGE_DURATION;
    }
    else
    {
        loop_metric = INVALID_EDGE_WEIGHT;
    }
    EdgeDistance loop_distance = MAXIMAL_EDGE_DISTANCE;
    for (auto edge : facade.GetAdjacentEdgeRange(node))
    {
        const auto &data = facade.GetEdgeData(edge);
        if (data.forward)
        {
            const NodeID to = facade.GetTarget(edge);
            if (to == node)
            {
                EdgeMetric value;
                if constexpr (std::is_same<EdgeMetric, EdgeDuration>::value)
                {
                    value = to_alias<EdgeDuration>(data.duration);
                }
                else
                {
                    value = data.weight;
                }
                if (value < loop_metric)
                {
                    loop_metric = value;
                    loop_distance = data.distance;
                }
            }
        }
    }
    return std::make_tuple(loop_metric, loop_distance);
}
} // namespace osrm::engine::routing_algorithms::ch

#endif // OSRM_ENGINE_ROUTING_BASE_CH_HPP
