/* 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.geometry.euclidean.threed.Vector3D;
  import org.hipparchus.util.FastMath;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.propagation.events.EventDetectionSettings;
  import org.orekit.propagation.events.EventDetector;
  
  import java.util.stream.Stream;
  
  /**
   * Fuel cost penalized with a quadratic term. For epsilon equal to 1, one gets the bounded energy cost.
   *
   * @author Romain Serra
   * @since 13.0
   * @see BoundedCartesianEnergy
   */
  public class QuadraticPenaltyCartesianFuel extends PenalizedCartesianFuelCost {
  
      /** Detection settings for singularity events. */
      private final EventDetectionSettings eventDetectionSettings;
  
      /**
       * Constructor.
       *
       * @param name                   adjoint name
       * @param massFlowRateFactor     mass flow rate factor
       * @param maximumThrustMagnitude maximum thrust magnitude
       * @param epsilon                penalty weight
       * @param eventDetectionSettings detection settings
       */
      public QuadraticPenaltyCartesianFuel(final String name, final double massFlowRateFactor,
                                           final double maximumThrustMagnitude, final double epsilon,
                                           final EventDetectionSettings eventDetectionSettings) {
          super(name, massFlowRateFactor, maximumThrustMagnitude, epsilon);
          this.eventDetectionSettings = eventDetectionSettings;
      }
  
      /**
       * Constructor with default event detection settings.
       *
       * @param name                   adjoint name
       * @param massFlowRateFactor     mass flow rate factor
       * @param maximumThrustMagnitude maximum thrust magnitude
       * @param epsilon                penalty weight
       */
      public QuadraticPenaltyCartesianFuel(final String name, final double massFlowRateFactor,
                                           final double maximumThrustMagnitude, final double epsilon) {
          this(name, massFlowRateFactor, maximumThrustMagnitude, epsilon,
                  EventDetectionSettings.getDefaultEventDetectionSettings());
      }
  
      /**
       * Getter for the event detection settings.
       * @return detection settings
       */
      public EventDetectionSettings getEventDetectionSettings() {
          return eventDetectionSettings;
      }
  
      /** {@inheritDoc} */
      @Override
      public double evaluatePenaltyFunction(final double controlNorm) {
          return controlNorm * (controlNorm * getMaximumThrustMagnitude() / 2 - 1.);
      }
  
      /** {@inheritDoc} */
      @Override
      public Vector3D getThrustAccelerationVector(final double[] adjointVariables, final double mass) {
          final double switchFunction = evaluateSwitchFunction(adjointVariables, mass);
          if (switchFunction > 0) {
              final double thrustForceMagnitude = FastMath.min(switchFunction, getMaximumThrustMagnitude());
              return getThrustDirection(adjointVariables).scalarMultiply(thrustForceMagnitude / mass);
          } else {
              return Vector3D.ZERO;
          }
      }
  
      /** {@inheritDoc} */
      @Override
      public void updateAdjointDerivatives(final double[] adjointVariables, final double mass,
                                           final double[] adjointDerivatives) {
          if (getAdjointDimension() > 6) {
             final double switchFunction = evaluateSwitchFunction(adjointVariables, mass);
             if (switchFunction > 0.) {
                 adjointDerivatives[6] += getAdjointVelocityNorm(adjointVariables) *
                         FastMath.min(switchFunction, getMaximumThrustMagnitude()) / (mass * mass);
             }
         }
     }
 
     /**
      * Evaluate switching function (whose value determines the control profile).
      * @param adjointVariables adjoint vector
      * @param mass mass
      * @return value of switch function
      */
     private double evaluateSwitchFunction(final double[] adjointVariables, final double mass) {
         double epsilonIndependentTerm = getAdjointVelocityNorm(adjointVariables) / mass - 1.;
         if (getAdjointDimension() > 6) {
             epsilonIndependentTerm -= getMassFlowRateFactor() * adjointVariables[6];
         }
         return epsilonIndependentTerm / getEpsilon() + 1.;
     }
 
     /** {@inheritDoc} */
     @Override
     public Stream<EventDetector> getEventDetectors() {
         return Stream.of(new QuadraticPenalizedSwitchDetector(getEventDetectionSettings(), 0),
                 new QuadraticPenalizedSwitchDetector(getEventDetectionSettings(), getMaximumThrustMagnitude()));
     }
 
     /**
      * Event detector for control non-differentiability.
      */
     private class QuadraticPenalizedSwitchDetector extends ControlSwitchDetector {
 
         /** Critical value at which the switching function has an event. */
         private final double criticalValue;
 
         /**
          * Constructor.
          * @param detectionSettings detection settings.
          * @param criticalValue switch function value to detect
          */
         QuadraticPenalizedSwitchDetector(final EventDetectionSettings detectionSettings,
                                          final double criticalValue) {
             super(detectionSettings);
             this.criticalValue = criticalValue;
         }
 
         /** {@inheritDoc} */
         @Override
         public double g(final SpacecraftState state) {
             final double[] adjoint = state.getAdditionalState(getAdjointName());
             return evaluateSwitchFunction(adjoint, state.getMass()) - criticalValue;
         }
     }
 }