Neighbour.hpp

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// This file is part of the Acts project.
//
// Copyright (C) 2023 CERN for the benefit of the Acts project
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

#pragma once

#include "Acts/Seeding/SpacePointGrid.hpp"

namespace Acts {


template <typename external_spacepoint_t>
struct Neighbour {
  Neighbour() = delete;

  Neighbour(Acts::SpacePointGrid<external_spacepoint_t>&& grid, std::size_t idx,
            const float lowerBound) = delete;

  Neighbour(const Acts::SpacePointGrid<external_spacepoint_t>& grid,
            std::size_t idx, const float lowerBound);

  std::size_t index;
  typename Acts::SpacePointGrid<
      external_spacepoint_t>::value_type::const_iterator itr;
};

template <typename external_spacepoint_t>
Neighbour<external_spacepoint_t>::Neighbour(
    const Acts::SpacePointGrid<external_spacepoint_t>& grid, std::size_t idx,
    const float lowerBound)
    : index(idx) {
  const auto& collection = grid.at(idx);
  if (collection.size() == 0) {
    itr = collection.begin();
    return;
  }

  if (collection.front()->radius() > lowerBound) {
    itr = collection.begin();
  }
  else if (collection.back()->radius() < lowerBound) {
    itr = collection.end();
  }
  else {
    itr = std::lower_bound(collection.begin(), collection.end(), lowerBound,
                           [](const auto& sp, const float target) -> bool {
                             return sp->radius() < target;
                           });
  }
}

}  // namespace Acts