/* 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.orekit.propagation.FieldSpacecraftState;
  import org.orekit.propagation.events.FieldEventDetectionSettings;
  
  /**
   * Abstract class for energy cost with Cartesian coordinates and non-zero mass flow rate.
   * An energy cost is proportional to the integral over time of the squared Euclidean norm of the control vector, often scaled with 1/2.
   * This type of cost is not optimal in terms of mass consumption, however its solutions showcase a smoother behavior favorable for convergence in shooting techniques.
   *
   * @param <T> field type
   * @author Romain Serra
   * @see FieldCartesianCost
   * @see CartesianEnergyConsideringMass
   * @since 13.0
   */
  abstract class FieldCartesianEnergyConsideringMass<T extends CalculusFieldElement<T>> extends FieldAbstractCartesianCost<T> {
  
      /** Detection settings for singularity detection. */
      private final FieldEventDetectionSettings<T> eventDetectionSettings;
  
      /**
       * Constructor.
       * @param name name
       * @param massFlowRateFactor mass flow rate factor
       * @param eventDetectionSettings settings for singularity detections
       */
      protected FieldCartesianEnergyConsideringMass(final String name, final T massFlowRateFactor,
                                                    final FieldEventDetectionSettings<T> eventDetectionSettings) {
          super(name, massFlowRateFactor);
          this.eventDetectionSettings = eventDetectionSettings;
      }
  
      /**
       * Getter for event detection settings.
       * @return detection settings.
       */
      public FieldEventDetectionSettings<T> getEventDetectionSettings() {
          return eventDetectionSettings;
      }
  
      /** {@inheritDoc} */
      @Override
      public FieldVector3D<T> getFieldThrustAccelerationVector(final T[] adjointVariables, final T mass) {
          return getFieldThrustDirection(adjointVariables).scalarMultiply(getFieldThrustForceNorm(adjointVariables, mass).divide(mass));
      }
  
      /**
       * Computes the direction of thrust.
       * @param adjointVariables adjoint vector
       * @return thrust direction
       */
      protected FieldVector3D<T> getFieldThrustDirection(final T[] adjointVariables) {
          return new FieldVector3D<>(adjointVariables[3], adjointVariables[4], adjointVariables[5]).normalize();
      }
  
      /**
       * Computes the Euclidean norm of the thrust force.
       * @param adjointVariables adjoint vector
       * @param mass mass
       * @return norm of thrust
       */
      protected abstract T getFieldThrustForceNorm(T[] adjointVariables, T mass);
  
      /** {@inheritDoc} */
      @Override
      public void updateFieldAdjointDerivatives(final T[] adjointVariables, final T mass, final T[] adjointDerivatives) {
          if (getAdjointDimension() > 6) {
              adjointDerivatives[6] = adjointDerivatives[6].add(getFieldThrustForceNorm(adjointVariables, mass)
                      .multiply(getFieldAdjointVelocityNorm(adjointVariables)).divide(mass.square()));
          }
      }
  
      /** {@inheritDoc} */
      @Override
      public T getFieldHamiltonianContribution(final T[] adjointVariables, final T mass) {
          final FieldVector3D<T> thrustForce = getFieldThrustAccelerationVector(adjointVariables, mass).scalarMultiply(mass);
          return thrustForce.getNormSq().multiply(-1. / 2.);
      }
  
     /**
      * Field event detector for singularities in adjoint dynamics.
      */
     class FieldSingularityDetector extends FieldControlSwitchDetector<T> {
 
         /** Value to detect. */
         private final T detectionValue;
 
         /**
          * Constructor.
          * @param detectionSettings detection settings
          * @param detectionValue value to detect
          */
         FieldSingularityDetector(final FieldEventDetectionSettings<T> detectionSettings, final T detectionValue) {
             super(detectionSettings);
             this.detectionValue = detectionValue;
         }
 
         /** {@inheritDoc} */
         @Override
         public T g(final FieldSpacecraftState<T> state) {
             final T[] adjoint = state.getAdditionalState(getAdjointName());
             return evaluateVariablePart(adjoint, state.getMass()).subtract(detectionValue);
         }
 
         /**
          * Evaluate variable part of singularity function.
          * @param adjointVariables adjoint vector
          * @param mass mass
          * @return singularity function without the constant part
          */
         private T evaluateVariablePart(final T[] adjointVariables, final T mass) {
             final T adjointVelocityNorm = getFieldAdjointVelocityNorm(adjointVariables);
             T variablePart = adjointVelocityNorm.divide(mass);
             if (getAdjointDimension() > 6) {
                 variablePart = variablePart.subtract(adjointVariables[6].multiply(getMassFlowRateFactor()));
             }
             return variablePart;
         }
 
     }
 }