// Ceres Solver - A fast non-linear least squares minimizer
// Copyright 2023 Google Inc. All rights reserved.
// http://ceres-solver.org/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// * Redistributions of source code must retain the above copyright notice,
//   this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above copyright notice,
//   this list of conditions and the following disclaimer in the documentation
//   and/or other materials provided with the distribution.
// * Neither the name of Google Inc. nor the names of its contributors may be
//   used to endorse or promote products derived from this software without
//   specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.
//
// Author: sameeragarwal@google.com (Sameer Agarwal)
//         mierle@gmail.com (Keir Mierle)
//         jodebo_beck@gmx.de (Johannes Beck)

#ifndef CERES_PUBLIC_INTERNAL_VARIADIC_EVALUATE_H_
#define CERES_PUBLIC_INTERNAL_VARIADIC_EVALUATE_H_

// IWYU pragma: private

#include <cstddef>
#include <type_traits>
#include <utility>

#include "Eigen/Core"
#include "ceres/cost_function.h"
#include "ceres/internal/parameter_dims.h"

namespace ceres::internal {

// VariadicEvaluate is a helper function to evaluate Ceres cost functions or
// functors using an input, output and the parameter dimensions. There are
// several possibilities:
// 1) If the passed functor is a 'ceres::CostFunction', its Evaluate method is
// called.
// 2) If the functor is not a 'ceres::CostFunction' and the specified parameter
// dimensions are dynamic, the functor must have the following signature:
// 'bool(T const* const* input, T* output)'.
// 3) If the functor is not a 'ceres::CostFunction' and the specified parameter
// dimensions are not dynamic, the input is expanded by using the number of
// parameter blocks. The signature of the functor must have the following
// signature:
// 'bool()(const T* i_1, const T* i_2, ... const T* i_n, T* output)'.
template <typename Functor, typename T, std::size_t... Is>
EIGEN_STRONG_INLINE bool VariadicEvaluateImpl(const Functor& functor,
                                              T const* const* input,
                                              T* output,
                                              std::index_sequence<Is...>) {
  static_assert(
      std::is_invocable_v<const Functor&,
                          decltype((void(Is), std::declval<const T*>()))...,
                          T*>,
      "The provided Functor's operator() signature does not match "
      "the expected number of parameter blocks defined in "
      "ParameterDims.");
  return functor(input[Is]..., output);
}

template <typename ParameterDims, typename Functor, typename T>
EIGEN_STRONG_INLINE bool VariadicEvaluate(const Functor& functor,
                                          T const* const* input,
                                          T* output) {
  if constexpr (std::is_base_of_v<CostFunction, Functor>) {
    return functor.Evaluate(input, output, nullptr);
  } else if constexpr (ParameterDims::kIsDynamic) {
    return functor(input, output);
  } else {
    constexpr int kNumParameterBlocks = ParameterDims::kNumParameterBlocks;
    static_assert(kNumParameterBlocks > 0,
                  "Invalid number of parameter blocks. At least one "
                  "parameter block must be specified.");
    return VariadicEvaluateImpl(
        functor,
        input,
        output,
        std::make_index_sequence<kNumParameterBlocks>{});
  }
}

// When differentiating dynamically sized CostFunctions, VariadicEvaluate
// expects a functor with the signature:
//
// bool operator()(double const* const* parameters, double* cost) const
//
// However for NumericDiffFirstOrderFunction, the functor has the signature
//
// bool operator()(double const* parameters, double* cost) const
//
// This thin wrapper adapts the latter to the former.
template <typename Functor>
class FirstOrderFunctorAdapter {
 public:
  explicit FirstOrderFunctorAdapter(const Functor& functor)
      : functor_(functor) {}
  bool operator()(double const* const* parameters, double* cost) const {
    return functor_(*parameters, cost);
  }

 private:
  const Functor& functor_;
};

}  // namespace ceres::internal

#endif  // CERES_PUBLIC_INTERNAL_VARIADIC_EVALUATE_H_