/* Copyright (c) 2008-2025 the MRtrix3 contributors.
 *
 * 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/.
 *
 * Covered Software is provided under this License on an "as is"
 * basis, without warranty of any kind, either expressed, implied, or
 * statutory, including, without limitation, warranties that the
 * Covered Software is free of defects, merchantable, fit for a
 * particular purpose or non-infringing.
 * See the Mozilla Public License v. 2.0 for more details.
 *
 * For more details, see http://www.mrtrix.org/.
 */

#ifndef __registration_metric_demons_h__
#define __registration_metric_demons_h__

#include <mutex>

#include "image_helpers.h"
#include "adapter/gradient3D.h"

namespace MR
{
  namespace Registration
  {
    namespace Metric
    {

      template <class Im1ImageType, class Im2ImageType, class Im1MaskType, class Im2MaskType>
      class Demons { MEMALIGN(Demons<Im1ImageType,Im2ImageType,Im1MaskType,Im2MaskType>)
        public:
          Demons (default_type& global_energy, size_t& global_voxel_count,
                     const Im1ImageType& im1_image, const Im2ImageType& im2_image, const Im1MaskType im1_mask, const Im2MaskType im2_mask) :
                       global_cost (global_energy),
                       global_voxel_count (global_voxel_count),
                       thread_cost (0.0),
                       thread_voxel_count (0),
                       mutex (new std::mutex),
                       normaliser (0.0),
                       robustness_parameter (1.e-12),
                       intensity_difference_threshold (0.001),
                       denominator_threshold (1e-9),
                       im1_gradient (im1_image, true), im2_gradient (im2_image, true),
                       im1_mask (im1_mask), im2_mask (im2_mask)
          {
            for (size_t d = 0; d < 3; ++d)
              normaliser += im1_image.spacing(d) * im2_image.spacing(d);
            normaliser /= 3.0;
          }

          ~Demons () {
            std::lock_guard<std::mutex> lock (*mutex);
            global_cost += thread_cost;
            global_voxel_count += thread_voxel_count;
          }

          void set_im1_mask (const Image<float>& mask) {
            im1_mask = mask;
          }

          void set_im2_mask (const Image<float>& mask) {
            im2_mask = mask;
          }


          void operator() (const Im1ImageType& im1_image,
                           const Im2ImageType& im2_image,
                           Image<default_type>& im1_update,
                           Image<default_type>& im2_update) {

            if (im1_image.index(0) == 0 || im1_image.index(0) == im1_image.size(0) - 1 ||
                im1_image.index(1) == 0 || im1_image.index(1) == im1_image.size(1) - 1 ||
                im1_image.index(2) == 0 || im1_image.index(2) == im1_image.size(2) - 1) {
              im1_update.row(3) = 0.0;
              im2_update.row(3) = 0.0;
              return;
            }

            typename Im1MaskType::value_type im1_mask_value = 1.0;
            if (im1_mask.valid()) {
              assign_pos_of (im1_image, 0, 3).to (im1_mask);
              im1_mask_value = im1_mask.value();
              if (im1_mask_value < 0.1) {
                im1_update.row(3) = 0.0;
                im2_update.row(3) = 0.0;
                return;
              }
            }

            typename Im2MaskType::value_type im2_mask_value = 1.0;
            if (im2_mask.valid()) {
              assign_pos_of (im2_image, 0, 3).to (im2_mask);
              im2_mask_value = im2_mask.value();
              if (im2_mask_value < 0.1) {
                im1_update.row(3) = 0.0;
                im2_update.row(3) = 0.0;
                return;
              }
            }


            default_type speed = im2_image.value() - im1_image.value();
            if (abs (speed) < robustness_parameter)
              speed = 0.0;

            default_type speed_squared = speed * speed;
            thread_cost += speed_squared;
            thread_voxel_count++;

            assign_pos_of (im1_image, 0, 3).to (im1_gradient, im2_gradient);

            Eigen::Matrix<typename Im1ImageType::value_type, 3, 1> grad = (im2_gradient.value() + im1_gradient.value()).array() / 2.0;
            default_type denominator = speed_squared / normaliser + grad.squaredNorm();
            if (abs (speed) < intensity_difference_threshold || denominator < denominator_threshold) {
              im1_update.row(3) = 0.0;
              im2_update.row(3) = 0.0;
            } else {
              im1_update.row(3) = Eigen::Vector3d (speed * grad.array() / denominator);
              im2_update.row(3) = -Eigen::Vector3d (im1_update.row(3));
            }
          }


          protected:
            default_type& global_cost;
            size_t& global_voxel_count;
            default_type thread_cost;
            size_t thread_voxel_count;
            std::shared_ptr<std::mutex> mutex;
            default_type normaliser;
            const default_type robustness_parameter;
            const default_type intensity_difference_threshold;
            const default_type denominator_threshold;

            Adapter::Gradient3D<Im1ImageType> im1_gradient;
            Adapter::Gradient3D<Im2ImageType> im2_gradient;
            Im1MaskType im1_mask;
            Im2MaskType im2_mask;

      };
    }
  }
}
#endif
