/* 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.cost;
  
  import org.hipparchus.CalculusFieldElement;
  import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  import org.hipparchus.util.FastMath;
  
  /**
   * Fuel cost penalized with a logarithmic term, which is a barrier so is not defined for epsilon equal to 0 or 1.
   *
   * @author Romain Serra
   * @since 13.0
   */
  public class FieldLogarithmicBarrierCartesianFuel<T extends CalculusFieldElement<T>>
          extends FieldPenalizedCartesianFuelCost<T> {
  
      /**
       * Constructor.
       *
       * @param name                   adjoint name
       * @param massFlowRateFactor     mass flow rate factor
       * @param maximumThrustMagnitude maximum thrust magnitude
       * @param epsilon                penalty weight
       */
      public FieldLogarithmicBarrierCartesianFuel(final String name, final T massFlowRateFactor,
                                                  final T maximumThrustMagnitude, final T epsilon) {
          super(name, massFlowRateFactor, maximumThrustMagnitude, epsilon);
      }
  
      /** {@inheritDoc} */
      @Override
      public T evaluateFieldPenaltyFunction(final T controlNorm) {
          return FastMath.log(controlNorm).add(FastMath.log(controlNorm.negate().add(1)));
      }
  
      /** {@inheritDoc} */
      @Override
      public FieldVector3D<T> getFieldThrustAccelerationVector(final T[] adjointVariables, final T mass) {
          final T thrustForceMagnitude = getThrustForceMagnitude(adjointVariables, mass);
          return getFieldThrustDirection(adjointVariables).scalarMultiply(thrustForceMagnitude.divide(mass));
      }
  
      /** {@inheritDoc} */
      @Override
      public void updateFieldAdjointDerivatives(final T[] adjointVariables, final T mass, final T[] adjointDerivatives) {
          if (getAdjointDimension() > 6) {
              adjointDerivatives[6] = adjointDerivatives[6].add(getFieldAdjointVelocityNorm(adjointVariables)
                      .multiply(getThrustForceMagnitude(adjointVariables, mass)).divide(mass.square()));
          }
      }
  
      /**
       * Computes the Euclidean norm of the thrust force.
       * @param adjointVariables adjoint variables
       * @param mass mass
       * @return thrust force magnitude
       */
      private T getThrustForceMagnitude(final T[] adjointVariables, final T mass) {
          final T twoEpsilon = getEpsilon().multiply(2);
          T otherTerm = getFieldAdjointVelocityNorm(adjointVariables).divide(mass).subtract(1.);
          if (getAdjointDimension() > 6) {
              otherTerm = otherTerm.subtract(getMassFlowRateFactor().multiply(adjointVariables[6]));
          }
          return twoEpsilon.multiply(getMaximumThrustMagnitude())
                  .divide(twoEpsilon.add(otherTerm).add(FastMath.sqrt(otherTerm.square().add(twoEpsilon.square()))));
      }
  
      /** {@inheritDoc} */
      @Override
      public LogarithmicBarrierCartesianFuel toCartesianCost() {
          return new LogarithmicBarrierCartesianFuel(getAdjointName(), getMassFlowRateFactor().getReal(),
                  getMaximumThrustMagnitude().getReal(), getEpsilon().getReal());
      }
  }