/* Copyright 2002-2025 CS GROUP
    * 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.propagation.integration;
  
  import java.util.ArrayList;
  import java.util.List;
  
  import org.hipparchus.Field;
  import org.hipparchus.analysis.differentiation.Gradient;
  import org.hipparchus.analysis.differentiation.GradientField;
  import org.hipparchus.geometry.euclidean.threed.FieldRotation;
  import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  import org.hipparchus.geometry.euclidean.threed.Vector3D;
  import org.orekit.attitudes.AttitudeProvider;
  import org.orekit.attitudes.FieldAttitude;
  import org.orekit.orbits.OrbitType;
  import org.orekit.orbits.FieldCartesianOrbit;
  import org.orekit.orbits.FieldEquinoctialOrbit;
  import org.orekit.orbits.FieldOrbit;
  import org.orekit.orbits.PositionAngleType;
  import org.orekit.propagation.FieldSpacecraftState;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.time.FieldAbsoluteDate;
  import org.orekit.utils.FieldAngularCoordinates;
  import org.orekit.utils.FieldPVCoordinates;
  import org.orekit.utils.FieldAbsolutePVCoordinates;
  import org.orekit.utils.ParameterDriver;
  import org.orekit.utils.ParameterDriversProvider;
  import org.orekit.utils.TimeStampedFieldAngularCoordinates;
  import org.orekit.utils.TimeStampedFieldPVCoordinates;
  import org.orekit.utils.TimeSpanMap.Span;
  
  /** Converter for states and parameters arrays.
   *  @author Luc Maisonobe
   *  @author Bryan Cazabonne
   *  @since 10.2
   */
  public abstract class AbstractGradientConverter {
  
      /** Dimension of the state. */
      private final int freeStateParameters;
  
      /** States with various number of additional parameters. */
      private final List<FieldSpacecraftState<Gradient>> gStates;
  
      /** Simple constructor.
       * @param freeStateParameters number of free parameters
       */
      protected AbstractGradientConverter(final int freeStateParameters) {
          this.freeStateParameters = freeStateParameters;
          this.gStates             = new ArrayList<>();
      }
  
      /** Get the number of free state parameters.
       * @return number of free state parameters
       */
      public int getFreeStateParameters() {
          return freeStateParameters;
      }
  
      /** Initialize first state with 0 parameters.
       * @param zeroParametersState state with zero parameters
       * @since 11.2
       */
      protected void initStates(final FieldSpacecraftState<Gradient> zeroParametersState) {
          gStates.clear();
          gStates.add(zeroParametersState);
      }
  
      /** Add zero derivatives.
       * @param original original scalar
       * @param freeParameters total number of free parameters in the gradient
       * @return extended scalar
       */
      protected Gradient extend(final Gradient original, final int freeParameters) {
          final double[] originalDerivatives = original.getGradient();
          final double[] extendedDerivatives = new double[freeParameters];
          System.arraycopy(originalDerivatives, 0, extendedDerivatives, 0, originalDerivatives.length);
          return new Gradient(original.getValue(), extendedDerivatives);
      }
  
      /**
       * Add zero derivatives.
       *
      * @param original       original date
      * @param freeParameters total number of free parameters in the gradient
      * @return extended date
      */
     protected FieldAbsoluteDate<Gradient> extend(final FieldAbsoluteDate<Gradient> original, final int freeParameters) {
         final AbsoluteDate date = original.toAbsoluteDate();
         final Gradient gradient = original.durationFrom(date);
         return new FieldAbsoluteDate<>(date, extend(gradient, freeParameters));
     }
 
     /** Add zero derivatives.
      * @param original original vector
      * @param freeParameters total number of free parameters in the gradient
      * @return extended vector
      */
     protected FieldVector3D<Gradient> extend(final FieldVector3D<Gradient> original, final int freeParameters) {
         return new FieldVector3D<>(extend(original.getX(), freeParameters),
                                    extend(original.getY(), freeParameters),
                                    extend(original.getZ(), freeParameters));
     }
 
     /** Add zero derivatives.
      * @param original original rotation
      * @param freeParameters total number of free parameters in the gradient
      * @return extended rotation
      */
     protected FieldRotation<Gradient> extend(final FieldRotation<Gradient> original, final int freeParameters) {
         return new FieldRotation<>(extend(original.getQ0(), freeParameters),
                                    extend(original.getQ1(), freeParameters),
                                    extend(original.getQ2(), freeParameters),
                                    extend(original.getQ3(), freeParameters),
                                    false);
     }
 
     /** Process a state into a Gradient version without force model parameter.
      * @param state state
      * @param freeStateParameters number of free parameters
      * @param provider attitude provider
      * @return Gradient version of the state
      * @since 12.0
      */
     protected static FieldSpacecraftState<Gradient> buildBasicGradientSpacecraftState(final SpacecraftState state,
                                                                                       final int freeStateParameters,
                                                                                       final AttitudeProvider provider) {
 
         // Derivative field
         final Field<Gradient> field =  GradientField.getField(freeStateParameters);
 
         // position always has derivatives
         final Vector3D pos = state.getPosition();
         final FieldVector3D<Gradient> posG = new FieldVector3D<>(Gradient.variable(freeStateParameters, 0, pos.getX()),
                                                                  Gradient.variable(freeStateParameters, 1, pos.getY()),
                                                                  Gradient.variable(freeStateParameters, 2, pos.getZ()));
 
         // velocity may have derivatives or not
         final Vector3D vel = state.getPVCoordinates().getVelocity();
         final FieldVector3D<Gradient> velG;
         if (freeStateParameters > 3) {
             velG = new FieldVector3D<>(Gradient.variable(freeStateParameters, 3, vel.getX()),
                                        Gradient.variable(freeStateParameters, 4, vel.getY()),
                                        Gradient.variable(freeStateParameters, 5, vel.getZ()));
         } else {
             velG = new FieldVector3D<>(field, vel);
         }
 
         // acceleration never has derivatives
         final Vector3D acc = state.getPVCoordinates().getAcceleration();
         final FieldVector3D<Gradient> accG = new FieldVector3D<>(field, acc);
 
         // mass never has derivatives
         final Gradient gMass = Gradient.constant(freeStateParameters, state.getMass());
 
         final TimeStampedFieldPVCoordinates<Gradient> timeStampedFieldPVCoordinates =
             new TimeStampedFieldPVCoordinates<>(state.getDate(), posG, velG, accG);
 
         final FieldCartesianOrbit<Gradient> gOrbit;
         final FieldAbsolutePVCoordinates<Gradient> gAbsolutePV;
         if (state.isOrbitDefined()) {
             final Gradient gMu = Gradient.constant(freeStateParameters, state.getOrbit().getMu());
             gOrbit = new FieldCartesianOrbit<>(timeStampedFieldPVCoordinates, state.getFrame(), gMu);
             gAbsolutePV = null;
         } else {
             gOrbit = null;
             gAbsolutePV = new FieldAbsolutePVCoordinates<>(state.getFrame(), timeStampedFieldPVCoordinates);
         }
 
         final FieldAttitude<Gradient> gAttitude;
         if (freeStateParameters > 3) {
             // compute attitude partial derivatives with respect to position/velocity
             gAttitude = provider.getAttitude((state.isOrbitDefined()) ? gOrbit : gAbsolutePV,
                                              timeStampedFieldPVCoordinates.getDate(), state.getFrame());
         } else {
             // force model does not depend on attitude, don't bother recomputing it
             gAttitude = new FieldAttitude<>(field, state.getAttitude());
         }
 
         if (state.isOrbitDefined()) {
             return new FieldSpacecraftState<>(gOrbit, gAttitude).withMass(gMass);
         } else {
             return new FieldSpacecraftState<>(gAbsolutePV, gAttitude).withMass(gMass);
         }
 
     }
 
     /**
      * Get the state with the number of parameters consistent with parametric model.
      * @param parametricModel parametric model
      * @return state with the number of parameters consistent with parametric model
      */
     public FieldSpacecraftState<Gradient> getState(final ParameterDriversProvider parametricModel) {
 
         // count the required number of parameters
         int nbParams = 0;
         for (final ParameterDriver driver : parametricModel.getParametersDrivers()) {
             if (driver.isSelected()) {
                 nbParams += driver.getNbOfValues();
             }
         }
 
         // fill in intermediate slots
         while (gStates.size() < nbParams + 1) {
             gStates.add(null);
         }
 
         if (gStates.get(nbParams) == null) {
             // it is the first time we need this number of parameters
             // we need to create the state
             final int freeParameters = freeStateParameters + nbParams;
             final FieldSpacecraftState<Gradient> s0 = gStates.get(0);
             final AbsoluteDate date = s0.getDate().toAbsoluteDate();
 
             // attitude
             final FieldAngularCoordinates<Gradient> ac0 = s0.getAttitude().getOrientation();
             final FieldAttitude<Gradient> gAttitude =
                     new FieldAttitude<>(s0.getAttitude().getReferenceFrame(),
                             new TimeStampedFieldAngularCoordinates<>(date,
                                     extend(ac0.getRotation(), freeParameters),
                                     extend(ac0.getRotationRate(), freeParameters),
                                     extend(ac0.getRotationAcceleration(), freeParameters)));
 
             // mass
             final Gradient gMass = extend(s0.getMass(), freeParameters);
 
             // orbit or absolute position-velocity coordinates
             final FieldPVCoordinates<Gradient> pv0 = s0.getPVCoordinates();
             final TimeStampedFieldPVCoordinates<Gradient> timeStampedFieldPVCoordinates = new TimeStampedFieldPVCoordinates<>(
                     date,
                     extend(pv0.getPosition(),     freeParameters),
                     extend(pv0.getVelocity(),     freeParameters),
                     extend(pv0.getAcceleration(), freeParameters));
             final FieldSpacecraftState<Gradient> spacecraftState;
             if (s0.isOrbitDefined()) {
                 final FieldOrbit<Gradient> orbit = s0.getOrbit();
                 if (orbit.getType().equals(OrbitType.EQUINOCTIAL)) {
                     // for DSST, which always uses EquinoctialOrbit, not CartesianOrbit
                     spacecraftState =
                         new FieldSpacecraftState<>(new FieldEquinoctialOrbit<>(extend(orbit.getA(), freeParameters),
                                                                                extend(orbit.getEquinoctialEx(), freeParameters),
                                                                                extend(orbit.getEquinoctialEy(), freeParameters),
                                                                                extend(orbit.getHx(), freeParameters),
                                                                                extend(orbit.getHy(), freeParameters),
                                                                                extend(orbit.getLM(), freeParameters),
                                                                                PositionAngleType.MEAN,
                                                                                s0.getFrame(),
                                                                                extend(s0.getDate(), freeParameters),
                                                                                extend(orbit.getMu(), freeParameters)),
                             gAttitude).withMass(gMass);
                 } else {
                     spacecraftState =
                         new FieldSpacecraftState<>(new FieldCartesianOrbit<>(timeStampedFieldPVCoordinates,
                                                                              s0.getFrame(),
                                                                              extend(orbit.getMu(), freeParameters)),
                                                    gAttitude).withMass(gMass);
                 }
             } else {
                 spacecraftState =
                     new FieldSpacecraftState<>(new FieldAbsolutePVCoordinates<>(s0.getFrame(),
                                                                                 timeStampedFieldPVCoordinates),
                                                gAttitude).withMass(gMass);
             }
 
             gStates.set(nbParams, spacecraftState);
 
         }
 
         return gStates.get(nbParams);
 
     }
 
     /** Get the parametric model parameters, return gradient values for each span of each driver (several gradient
      * values for each parameter).
      * Different from {@link #getParametersAtStateDate(FieldSpacecraftState, ParameterDriversProvider)}
      * which return a Gradient list containing for each driver the gradient value at state date (only 1 gradient
      * value for each parameter).
      * @param state state as returned by {@link #getState(ParameterDriversProvider) getState(parametricModel)}
      * @param parametricModel parametric model associated with the parameters
      * @return parametric model parameters (for all span of each driver)
      */
     public Gradient[] getParameters(final FieldSpacecraftState<Gradient> state,
                                     final ParameterDriversProvider parametricModel) {
         final int freeParameters = state.getMass().getFreeParameters();
         final List<ParameterDriver> drivers = parametricModel.getParametersDrivers();
         int sizeDrivers = 0;
         for ( ParameterDriver driver : drivers) {
             sizeDrivers += driver.getNbOfValues();
         }
         final Gradient[] parameters = new Gradient[sizeDrivers];
         int index = freeStateParameters;
         int i = 0;
         for (ParameterDriver driver : drivers) {
             // Loop on the spans
             for (Span<Double> span = driver.getValueSpanMap().getFirstSpan(); span != null; span = span.next()) {
                 parameters[i++] = driver.isSelected() ?
                                   Gradient.variable(freeParameters, index++, span.getData()) :
                                   Gradient.constant(freeParameters, span.getData());
             }
         }
         return parameters;
     }
 
     /** Get the parametric model parameters, return gradient values at state date for each driver (only 1 gradient
      * value for each parameter).
      * Different from {@link #getParameters(FieldSpacecraftState, ParameterDriversProvider)}
      * which return a Gradient list containing for each driver the gradient values for each span value (several gradient
      * values for each parameter).
      * @param state state as returned by {@link #getState(ParameterDriversProvider) getState(parametricModel)}
      * @param parametricModel parametric model associated with the parameters
      * @return parametric model parameters (for all span of each driver)
      */
     public Gradient[] getParametersAtStateDate(final FieldSpacecraftState<Gradient> state,
             final ParameterDriversProvider parametricModel) {
         final int freeParameters = state.getMass().getFreeParameters();
         final List<ParameterDriver> drivers = parametricModel.getParametersDrivers();
 
         final Gradient[] parameters = new Gradient[drivers.size()];
         int index = freeStateParameters;
         int i = 0;
         for (ParameterDriver driver : drivers) {
             for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
                 if (span.getData().equals(driver.getNameSpan(state.getDate().toAbsoluteDate()))) {
                     parameters[i++] = driver.isSelected() ?
                                           Gradient.variable(freeParameters, index, driver.getValue(state.getDate().toAbsoluteDate())) :
                                           Gradient.constant(freeParameters, driver.getValue(state.getDate().toAbsoluteDate()));
                 }
                 index = driver.isSelected() ? index + 1 : index;
             }
         }
         return parameters;
     }
 
 
 }