/* Copyright 2022-2025 Romain Serra
    * Licensed to CS GROUP (CS) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * CS licenses this file to You 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.
   */
  package org.orekit.control.indirect.adjoint;
  
  import org.hipparchus.CalculusFieldElement;
  import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  import org.hipparchus.geometry.euclidean.threed.Vector3D;
  import org.hipparchus.util.FastMath;
  import org.hipparchus.util.MathArrays;
  import org.orekit.frames.Frame;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.time.FieldAbsoluteDate;
  import org.orekit.utils.ExtendedPositionProvider;
  
  /**
   * Class defining the contributions of a point-mass, third body in the adjoint equations for Cartesian coordinates.
   * If present, then the propagator should also include a {@link org.orekit.forces.gravity.ThirdBodyAttraction}.
   * @author Romain Serra
   * @see CartesianAdjointEquationTerm
   * @see org.orekit.forces.gravity.ThirdBodyAttraction
   * @since 12.2
   */
  public class CartesianAdjointThirdBodyTerm extends AbstractCartesianAdjointNonCentralBodyTerm {
  
      /**
       * Constructor.
       * @param mu body gravitational parameter.
       * @param bodyPositionProvider body position provider
       */
      public CartesianAdjointThirdBodyTerm(final double mu, final ExtendedPositionProvider bodyPositionProvider) {
          super(mu, bodyPositionProvider);
      }
  
      /** {@inheritDoc} */
      @Override
      public Vector3D getAcceleration(final AbsoluteDate date, final double[] stateVariables,
                                      final Frame frame) {
          final Vector3D bodyPosition = getBodyPosition(date, frame);
          final double x = stateVariables[0] - bodyPosition.getX();
          final double y = stateVariables[1] - bodyPosition.getY();
          final double z = stateVariables[2] - bodyPosition.getZ();
          final Vector3D newtonianAcceleration = getNewtonianAcceleration(new double[] {x, y, z});
          final double rBody2 = bodyPosition.getNormSq();
          final Vector3D bodyCentralAcceleration = bodyPosition.scalarMultiply(getMu() / (rBody2 * FastMath.sqrt(rBody2)));
          return newtonianAcceleration.subtract(bodyCentralAcceleration);
      }
  
      /** {@inheritDoc} */
      @Override
      public <T extends CalculusFieldElement<T>> FieldVector3D<T> getFieldAcceleration(final FieldAbsoluteDate<T> date,
                                                                                       final T[] stateVariables,
                                                                                       final Frame frame) {
          final FieldVector3D<T> bodyPosition = getFieldBodyPosition(date, frame);
          final T x = stateVariables[0].subtract(bodyPosition.getX());
          final T y = stateVariables[1].subtract(bodyPosition.getY());
          final T z = stateVariables[2].subtract(bodyPosition.getZ());
          final T[] relativePosition = MathArrays.buildArray(date.getField(), 3);
          relativePosition[0] = x;
          relativePosition[1] = y;
          relativePosition[2] = z;
          final FieldVector3D<T> newtonianAcceleration = getFieldNewtonianAcceleration(relativePosition);
          final T rBody2 = bodyPosition.getNormSq();
          final T factor = rBody2.multiply(rBody2.sqrt()).reciprocal().multiply(getMu());
          final FieldVector3D<T> bodyCentralAcceleration = bodyPosition.scalarMultiply(factor);
          return newtonianAcceleration.subtract(bodyCentralAcceleration);
      }
  }