////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2014-2023, Lawrence Livermore National Security, LLC.
// Produced at the Lawrence Livermore National Laboratory.
// Written by the LBANN Research Team (B. Van Essen, et al.) listed in
// the CONTRIBUTORS file. <lbann-dev@llnl.gov>
//
// LLNL-CODE-697807.
// All rights reserved.
//
// This file is part of LBANN: Livermore Big Artificial Neural Network
// Toolkit. For details, see http://software.llnl.gov/LBANN or
// https://github.com/LLNL/LBANN.
//
// Licensed under the Apache License, Version 2.0 (the "Licensee"); you
// may not use this file except in compliance with the License.  You may
// obtain a copy of the License at:
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
// implied. See the License for the specific language governing
// permissions and limitations under the license.
////////////////////////////////////////////////////////////////////////////////

#ifndef LBANN_LAYER_REDUCTION_HPP_INCLUDED
#define LBANN_LAYER_REDUCTION_HPP_INCLUDED

#include "lbann/layers/data_type_layer.hpp"

namespace lbann {

enum class reduction_mode
{
  INVALID,
  SUM,
  AVERAGE
};

/** @brief Reduce tensor to scalar
 *
 *  @todo Reduction over specified dimensions.
 */
template <typename TensorDataType,
          data_layout Layout = data_layout::DATA_PARALLEL,
          El::Device Device = El::Device::CPU>
class reduction_layer : public data_type_layer<TensorDataType>
{
private:
  /** Reduction mode. */
  reduction_mode m_mode;

public:
  reduction_layer(reduction_mode mode = reduction_mode::SUM);

  reduction_layer* copy() const override { return new reduction_layer(*this); }

  /** @name Serialization */
  ///@{

  template <typename ArchiveT>
  void serialize(ArchiveT& ar);

  ///@}

  std::string get_type() const override { return "reduction"; }
  data_layout get_data_layout() const override { return Layout; }
  El::Device get_device_allocation() const override { return Device; }

  description get_description() const override
  {
    auto desc = data_type_layer<TensorDataType>::get_description();
    std::string mode_str;
    switch (m_mode) {
    case reduction_mode::SUM:
      mode_str = "sum";
      break;
    case reduction_mode::AVERAGE:
      mode_str = "average";
      break;
    case reduction_mode::INVALID:
    default:
      mode_str = "invalid";
    }
    desc.add("Mode", mode_str);
    return desc;
  }

protected:
  /** Add layer specific data to prototext */
  void write_specific_proto(lbann_data::Layer& proto) const final;

  void setup_dims(DataReaderMetaData& dr_metadata) override;

  void fp_compute() override;

  void bp_compute() override;
};

#ifndef LBANN_REDUCTION_LAYER_INSTANTIATE
#define PROTO_DEVICE(T, Device)                                                \
  extern template class reduction_layer<T,                                     \
                                        data_layout::DATA_PARALLEL,            \
                                        Device>;                               \
  extern template class reduction_layer<T, data_layout::MODEL_PARALLEL, Device>
#include "lbann/macros/instantiate_device.hpp"
#undef PROTO_DEVICE
#endif // LBANN_REDUCTION_LAYER_INSTANTIATE

} // namespace lbann

#endif // LBANN_LAYER_REDUCTION_HPP_INCLUDED
