////////////////////////////////////////////////////////////////////////////////
// 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_CALLBACKS_CALLBACK_CHECK_GRADIENTS_HPP_INCLUDED
#define LBANN_CALLBACKS_CALLBACK_CHECK_GRADIENTS_HPP_INCLUDED

#include "lbann/callbacks/callback.hpp"

#include <google/protobuf/message.h>

#include <set>

namespace lbann {
namespace callback {

/** @brief Gradient checking callback.
 *
 *  Gradient checking is performed at the end of each execution mode
 *  phase. Using a fourth-order finite difference scheme, a numerical
 *  partial derivative is computed for every weight parameter. If the
 *  numerical derivative differs signifcantly from the analytical
 *  derivative computed during backprop, the gradient check has
 *  failed.
 */
class check_gradients : public callback_base
{
public:
  /**
   *  @param modes              Execution modes with gradient checks. If
   *                            none are provided, gradient checking is
   *                            performed for every execution mode.
   *  @param step_size          Step size for numerical
   *                            differentiation (with a step size of
   *                            zero, the step size is estimated to
   *                            minimize the numerical error).
   *  @param verbose            Whether to print results for each
   *                            parameter.
   *  @param error_on_failure   Whether to throw an exception for
   *                            large gradient errors.
   */
  check_gradients(std::set<execution_mode> modes = {},
                  DataType step_size = DataType(0),
                  bool verbose = false,
                  bool error_on_failure = false);
  check_gradients* copy() const override { return new check_gradients(*this); }
  std::string name() const override { return "check gradients"; }
  void on_train_end(model* m) override { do_check_gradients(*m); }
  void on_validation_end(model* m) override { do_check_gradients(*m); }
  void on_test_end(model* m) override { do_check_gradients(*m); }

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

  /** @brief Store state to archive for checkpoint and restart */
  template <class Archive>
  void serialize(Archive& ar);

  ///@}

private:
  /** Add callback specific data to prototext */
  void write_specific_proto(lbann_data::Callback& proto) const final;

  /** Execution modes with gradient checks. */
  std::set<execution_mode> m_modes;
  /** Step size for numerical differentiation. */
  EvalType m_step_size;
  /** Whether to print results for each parameter. */
  bool m_verbose;
  /** Whether to throw an exception for large gradient errors. */
  bool m_error_on_failure;

  /** Does nothing if current execution mode is not in m_modes. */
  void do_check_gradients(model& m) const;
};

// Builder function
std::unique_ptr<callback_base>
build_check_gradients_callback_from_pbuf(const google::protobuf::Message&,
                                         std::shared_ptr<lbann_summary> const&);

} // namespace callback
} // namespace lbann

#endif // LBANN_CALLBACKS_CALLBACK_CHECK_GRADIENTS_HPP_INCLUDED
