/* 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.Field;
  import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  import org.orekit.propagation.FieldSpacecraftState;
  import org.orekit.propagation.events.EventDetectionSettings;
  import org.orekit.propagation.events.FieldEventDetectionSettings;
  import org.orekit.propagation.events.FieldEventDetector;
  
  import java.util.stream.Stream;
  
  /**
   * Class for fuel cost with Cartesian coordinates.
   * It is the integral over time of the Euclidean norm of the thrust vector.
   *
   * @author Romain Serra
   * @see CartesianCost
   * @since 13.0
   */
  public class FieldCartesianFuelCost<T extends CalculusFieldElement<T>> extends FieldAbstractCartesianCost<T> {
  
      /** Maximum value of thrust force Euclidean norm. */
      private final T maximumThrustMagnitude;
  
      /** Detection settings for singularity detection. */
      private final FieldEventDetectionSettings<T> eventDetectionSettings;
  
      /**
       * Constructor with default detection settings.
       * @param name name
       * @param massFlowRateFactor mass flow rate factor
       * @param maximumThrustMagnitude maximum thrust magnitude
       */
      public FieldCartesianFuelCost(final String name, final T massFlowRateFactor, final T maximumThrustMagnitude) {
          this(name, massFlowRateFactor, maximumThrustMagnitude, new FieldEventDetectionSettings<>(massFlowRateFactor.getField(),
                  EventDetectionSettings.getDefaultEventDetectionSettings()));
      }
  
      /**
       * Constructor.
       * @param name name
       * @param massFlowRateFactor mass flow rate factor
       * @param maximumThrustMagnitude maximum thrust magnitude
       * @param eventDetectionSettings singularity event detection settings
       */
      public FieldCartesianFuelCost(final String name, final T massFlowRateFactor, final T maximumThrustMagnitude,
                                    final FieldEventDetectionSettings<T> eventDetectionSettings) {
          super(name, massFlowRateFactor);
          this.maximumThrustMagnitude = maximumThrustMagnitude;
          this.eventDetectionSettings = eventDetectionSettings;
      }
  
      /**
       * Getter for event detection settings.
       * @return detection settings.
       */
      public FieldEventDetectionSettings<T> getEventDetectionSettings() {
          return eventDetectionSettings;
      }
  
      /** Getter for maximum thrust magnitude.
       * @return maximum thrust
       */
      public T getMaximumThrustMagnitude() {
          return maximumThrustMagnitude;
      }
  
      /**
       * Evaluate switching function (whose sign determines the bang-bang control profile).
       * @param adjointVariables adjoint vector
       * @param mass mass
       * @return value of switch function
       */
      private T evaluateFieldSwitchFunction(final T[] adjointVariables, final T mass) {
          T switchFunction = getFieldAdjointVelocityNorm(adjointVariables).divide(mass).subtract(1.);
          if (getAdjointDimension() > 6) {
              switchFunction = switchFunction.subtract(adjointVariables[6].multiply(getMassFlowRateFactor()));
          }
          return switchFunction;
      }
  
     /**
      * Computes the direction of thrust.
      * @param adjointVariables adjoint vector
      * @return thrust direction
      */
     private FieldVector3D<T> getFieldThrustDirection(final T[] adjointVariables) {
         return new FieldVector3D<>(adjointVariables[3], adjointVariables[4], adjointVariables[5]).normalize();
     }
 
     /** {@inheritDoc} */
     @Override
     public FieldVector3D<T> getFieldThrustAccelerationVector(final T[] adjointVariables, final T mass) {
         final T switchFunction = evaluateFieldSwitchFunction(adjointVariables, mass);
         if (switchFunction.getReal() > 0.) {
             return getFieldThrustDirection(adjointVariables).scalarMultiply(mass.reciprocal().multiply(maximumThrustMagnitude));
         } else {
             return FieldVector3D.getZero(mass.getField());
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public void updateFieldAdjointDerivatives(final T[] adjointVariables, final T mass,
                                               final T[] adjointDerivatives) {
         if (getAdjointDimension() > 6) {
             final T switchFunction = evaluateFieldSwitchFunction(adjointVariables, mass);
             if (switchFunction.getReal() > 0.) {
                 adjointDerivatives[6] = adjointDerivatives[6].add(getFieldAdjointVelocityNorm(adjointVariables)
                         .multiply(maximumThrustMagnitude).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.getNorm().negate();
     }
 
     /** {@inheritDoc} */
     @Override
     public Stream<FieldEventDetector<T>> getFieldEventDetectors(final Field<T> field) {
         return Stream.of(new FieldSwitchDetector(getEventDetectionSettings()));
     }
 
     @Override
     public CartesianFuelCost toCartesianCost() {
         return new CartesianFuelCost(getAdjointName(), getMassFlowRateFactor().getReal(), maximumThrustMagnitude.getReal(),
                 getEventDetectionSettings().toEventDetectionSettings());
     }
 
     /**
      * Field event detector for bang-bang switches.
      */
     class FieldSwitchDetector extends FieldControlSwitchDetector<T> {
 
         FieldSwitchDetector(final FieldEventDetectionSettings<T> detectionSettings) {
             super(detectionSettings);
         }
 
         /** {@inheritDoc} */
         @Override
         public T g(final FieldSpacecraftState<T> state) {
             final T[] adjoint = state.getAdditionalState(getAdjointName());
             return evaluateFieldSwitchFunction(adjoint, state.getMass());
         }
 
     }
 }