/*
 * Copyright 2018 The Cartographer Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * 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 CARTOGRAPHER_MAPPING_3D_POSE_GRAPH_LANDMARK_COST_FUNCTION_H_
#define CARTOGRAPHER_MAPPING_3D_POSE_GRAPH_LANDMARK_COST_FUNCTION_H_

#include "Eigen/Core"
#include "Eigen/Geometry"
#include "cartographer/mapping/pose_graph/cost_helpers.h"
#include "cartographer/mapping/pose_graph_interface.h"
#include "cartographer/mapping_3d/pose_graph/optimization_problem.h"
#include "cartographer/transform/rigid_transform.h"
#include "cartographer/transform/transform.h"
#include "ceres/ceres.h"
#include "ceres/jet.h"

namespace cartographer {
namespace mapping_3d {
namespace pose_graph {

// Cost function measuring the weighted error between the observed pose given by
// the landmark measurement and the linearly interpolated pose.
class LandmarkCostFunction {
 public:
  using LandmarkObservation =
      mapping::PoseGraphInterface::LandmarkNode::LandmarkObservation;

  static ceres::CostFunction* CreateAutoDiffCostFunction(
      const LandmarkObservation& observation, const NodeData& prev_node,
      const NodeData& next_node) {
    return new ceres::AutoDiffCostFunction<
        LandmarkCostFunction, 6 /* residuals */,
        4 /* previous node rotation variables */,
        3 /* previous node translation variables */,
        4 /* next node rotation variables */,
        3 /* next node translation variables */,
        4 /* landmark rotation variables */,
        3 /* landmark translation variables */>(
        new LandmarkCostFunction(observation, prev_node, next_node));
  }

  template <typename T>
  bool operator()(const T* const prev_node_rotation,
                  const T* const prev_node_translation,
                  const T* const next_node_rotation,
                  const T* const next_node_translation,
                  const T* const landmark_rotation,
                  const T* const landmark_translation, T* const e) const {
    using mapping::pose_graph::ComputeUnscaledError;
    using mapping::pose_graph::ScaleError;
    using mapping::pose_graph::SlerpQuaternions;

    const std::array<T, 3> interpolated_pose_translation{
        {prev_node_translation[0] +
             interpolation_parameter_ *
                 (next_node_translation[0] - prev_node_translation[0]),
         prev_node_translation[1] +
             interpolation_parameter_ *
                 (next_node_translation[1] - prev_node_translation[1]),
         prev_node_translation[2] +
             interpolation_parameter_ *
                 (next_node_translation[2] - prev_node_translation[2])}};
    const std::array<T, 4> interpolated_pose_rotation = SlerpQuaternions(
        prev_node_rotation, next_node_rotation, T(interpolation_parameter_));

    const std::array<T, 6> error = ScaleError(
        ComputeUnscaledError(landmark_to_tracking_transform_,
                             interpolated_pose_rotation.data(),
                             interpolated_pose_translation.data(),
                             landmark_rotation, landmark_translation),
        T(translation_weight_), T(rotation_weight_));
    std::copy(std::begin(error), std::end(error), e);
    return true;
  }

 private:
  LandmarkCostFunction(const LandmarkObservation& observation,
                       const NodeData& prev_node, const NodeData& next_node)
      : landmark_to_tracking_transform_(
            observation.landmark_to_tracking_transform),
        translation_weight_(observation.translation_weight),
        rotation_weight_(observation.rotation_weight),
        interpolation_parameter_(
            common::ToSeconds(observation.time - prev_node.time) /
            common::ToSeconds(next_node.time - prev_node.time)) {}

  const transform::Rigid3d landmark_to_tracking_transform_;
  const double translation_weight_;
  const double rotation_weight_;
  const double interpolation_parameter_;
};

}  // namespace pose_graph
}  // namespace mapping_3d
}  // namespace cartographer

#endif  // CARTOGRAPHER_MAPPING_3D_POSE_GRAPH_LANDMARK_COST_FUNCTION_H_