// ----------------------------------------------------------------------------
// -                        Open3D: www.open3d.org                            -
// ----------------------------------------------------------------------------
// Copyright (c) 2018-2023 www.open3d.org
// SPDX-License-Identifier: MIT
// ----------------------------------------------------------------------------

#pragma once

#include <Eigen/Core>
#include <memory>
#include <vector>

#include "open3d/geometry/Geometry.h"
#include "open3d/geometry/KDTreeSearchParam.h"
#include "open3d/pipelines/registration/Feature.h"

/// @cond
namespace nanoflann {
struct metric_L2;
template <class MatrixType, int DIM, class Distance, bool row_major>
struct KDTreeEigenMatrixAdaptor;
}  // namespace nanoflann
/// @endcond

namespace open3d {
namespace geometry {

/// \class KDTreeFlann
///
/// \brief KDTree with FLANN for nearest neighbor search.
class KDTreeFlann {
public:
    /// \brief Default Constructor.
    KDTreeFlann();
    /// \brief Parameterized Constructor.
    ///
    /// \param data Provides set of data points for KDTree construction.
    KDTreeFlann(const Eigen::MatrixXd &data);
    /// \brief Parameterized Constructor.
    ///
    /// \param geometry Provides geometry from which KDTree is constructed.
    KDTreeFlann(const Geometry &geometry);
    /// \brief Parameterized Constructor.
    ///
    /// \param feature Provides a set of features from which the KDTree is
    /// constructed.
    KDTreeFlann(const pipelines::registration::Feature &feature);
    ~KDTreeFlann();
    KDTreeFlann(const KDTreeFlann &) = delete;
    KDTreeFlann &operator=(const KDTreeFlann &) = delete;

public:
    /// Sets the data for the KDTree from a matrix.
    ///
    /// \param data Data points for KDTree Construction.
    bool SetMatrixData(const Eigen::MatrixXd &data);
    /// Sets the data for the KDTree from geometry.
    ///
    /// \param geometry Geometry for KDTree Construction.
    bool SetGeometry(const Geometry &geometry);
    /// Sets the data for the KDTree from the feature data.
    ///
    /// \param feature Set of features for KDTree construction.
    bool SetFeature(const pipelines::registration::Feature &feature);

    template <typename T>
    int Search(const T &query,
               const KDTreeSearchParam &param,
               std::vector<int> &indices,
               std::vector<double> &distance2) const;

    template <typename T>
    int SearchKNN(const T &query,
                  int knn,
                  std::vector<int> &indices,
                  std::vector<double> &distance2) const;

    template <typename T>
    int SearchRadius(const T &query,
                     double radius,
                     std::vector<int> &indices,
                     std::vector<double> &distance2) const;

    template <typename T>
    int SearchHybrid(const T &query,
                     double radius,
                     int max_nn,
                     std::vector<int> &indices,
                     std::vector<double> &distance2) const;

private:
    /// \brief Sets the KDTree data from the data provided by the other methods.
    ///
    /// Internal method that sets all the members of KDTree by data provided by
    /// features, geometry, etc.
    bool SetRawData(const Eigen::Map<const Eigen::MatrixXd> &data);

protected:
    using KDTree_t = nanoflann::KDTreeEigenMatrixAdaptor<const Eigen::MatrixXd,
                                                         -1,
                                                         nanoflann::metric_L2,
                                                         false>;

    Eigen::MatrixXd data_;
    std::unique_ptr<KDTree_t> nanoflann_index_;
};

}  // namespace geometry
}  // namespace open3d