ParametersSmearer.hpp

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// This file is part of the Acts project.
//
// Copyright (C) 2020 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 <utility>

#include "Acts/Utilities/Definitions.hpp"
#include "Acts/Utilities/ParameterDefinitions.hpp"
#include "Acts/Utilities/Result.hpp"

namespace ActsFatras {

namespace detail {

using SmearFunction =
    std::function<Acts::Result<std::pair<double, double>>(double)>;

template <typename values_t, typename covariance_t>
struct SingleComponentSmearer {
  void operator()(size_t idx, Eigen::MatrixBase<values_t>& values,
                  Eigen::MatrixBase<covariance_t>& covariances,
                  const SmearFunction& sFunction, Acts::Result<void>& result) {
    auto sResult = sFunction(values[idx]);
    if (sResult.ok()) {
      const auto& smeared = sResult.value();
      values[idx] = smeared.first;
      covariances(idx, idx) = smeared.second * smeared.second;
    } else {
      result = Acts::Result<void>(sResult.error());
    }
  }
};

template <typename indices_t, indices_t... kParameters>
struct ParametersSmearer {
  using StorageSequence = std::make_index_sequence<sizeof...(kParameters)>;

  template <typename values_t, typename covariance_t>
  static Acts::Result<void> run(
      Eigen::MatrixBase<values_t>& values,
      Eigen::MatrixBase<covariance_t>& covariances,
      const std::array<SmearFunction, sizeof...(kParameters)>& sFunctions) {
    return runImpl(values, covariances, sFunctions, StorageSequence{});
  }

  template <typename values_t, typename covariance_t, std::size_t... kStorage>
  static Acts::Result<void> runImpl(
      Eigen::MatrixBase<values_t>& values,
      Eigen::MatrixBase<covariance_t>& covariances,
      const std::array<SmearFunction, sizeof...(kParameters)>& sFunctions,
      std::index_sequence<kStorage...>) {
    EIGEN_STATIC_ASSERT_VECTOR_SPECIFIC_SIZE(values_t, sizeof...(kParameters));
    EIGEN_STATIC_ASSERT_MATRIX_SPECIFIC_SIZE(
        covariance_t, sizeof...(kParameters), sizeof...(kParameters));
    static_assert(sizeof...(kParameters) == sizeof...(kStorage),
                  "Parameters and storage index packs must have the same size");

    Acts::Result<void> result;
    SingleComponentSmearer<values_t, covariance_t> scs;
    ((scs(kStorage, values, covariances, sFunctions[kStorage], result)), ...);
    return result;
  }
};

}  // namespace detail
}  // namespace ActsFatras