/*
 * DynKatzCentrality.hpp
 *
 *  Created on: April 2018
 *      Author: Alexander van der Grinten
 *      based on code by Elisabetta Bergamini
 */

#ifndef NETWORKIT_CENTRALITY_DYN_KATZ_CENTRALITY_HPP_
#define NETWORKIT_CENTRALITY_DYN_KATZ_CENTRALITY_HPP_

#include <span>

#include <networkit/auxiliary/PrioQueue.hpp>
#include <networkit/base/DynAlgorithm.hpp>
#include <networkit/centrality/Centrality.hpp>
#include <networkit/dynamics/GraphEvent.hpp>

namespace NetworKit {

/**
 * @ingroup centrality
 * Finds the top-k nodes with highest Katz centrality
 */
class DynKatzCentrality : public Centrality, public DynAlgorithm {
protected:
    double alpha; // damping
    count k;
    count maxdeg;
    bool groupOnly;

    // Nodes that have Katz score that only differ by this constant might appear
    // swapped in the ranking.
    double rankTolerance;

public:
    bool useQueue = false;

public:
    /**
     * Constructs a DynKatzCentrality object for the given Graph @a G. The damping
     * factor is set to 1/(maxdeg + 1), where maxdeg is the maxmum degree in the
     * graph.
     *
     * @param[in] G The graph.
     * @param[in] k The number k for which we want to find the top-k nodes with
     * highest Katz centrality
     * @param[in] groupOnly Set whether the update will only update top-k nodes.
     * @param[in] tolerance The tolerance for convergence.
     */
    DynKatzCentrality(const Graph &G, count k, bool groupOnly = false, double tolerance = 1e-9);

    void run() override;

    /**
     * Updates the katz centralities after an edge insertion or deletion on the
     * graph.
     *
     * @param event The edge insertions or deletion.
     */
    void updateBatch(std::span<const GraphEvent> events) override;

    void update(GraphEvent singleEvent) override {
        std::vector<GraphEvent> events{singleEvent};
        updateBatch(events);
    }

    node top(count n = 0) {
        assert(activeRanking.size() > n);
        return activeRanking[n];
    }

    /**
     * Returns the (upper) bound of the centrality of each node
     */
    double bound(node v);

    /**
     * Returns true if the bounds are sharp enough to rank two nodes against each
     * other.
     */
    bool areDistinguished(node u, node v);

private:
    /**
     * Returns true if the bounds are sharp enough to rank two nodes against
     * each other **within the tolerance**.
     * Precondition: The first node appears higher in the current ranking the the
     * second one.
     */
    bool areSufficientlyRanked(node high, node low);

    /**
     * Performs a single iteration of the algorithm.
     */
    void doIteration();

    /**
     * Returns true iff the ranking converged for the top-k.
     */
    bool checkConvergence();

    std::vector<bool> isActive;
    std::vector<node> activeRanking;
    Aux::PrioQueue<double, node> activeQueue;
    bool filledQueue = false;

    std::vector<double> baseData;
    std::vector<double> boundData;

public: // TODO: This is public because tests access it.
    std::vector<std::vector<count>> nPaths;
    count levelReached = 0;
};

} /* namespace NetworKit */
#endif // NETWORKIT_CENTRALITY_DYN_KATZ_CENTRALITY_HPP_
