/* Copyright 2002-2021 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.
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  package org.orekit.propagation.semianalytical.dsst;
  
  import java.util.ArrayList;
  import java.util.List;
  
  import org.hipparchus.analysis.differentiation.Gradient;
  import org.hipparchus.analysis.differentiation.GradientField;
  import org.orekit.attitudes.AttitudeProvider;
  import org.orekit.attitudes.FieldAttitude;
  import org.orekit.orbits.FieldEquinoctialOrbit;
  import org.orekit.orbits.FieldOrbit;
  import org.orekit.orbits.PositionAngle;
  import org.orekit.propagation.FieldSpacecraftState;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.propagation.integration.AbstractGradientConverter;
  import org.orekit.propagation.semianalytical.dsst.forces.DSSTForceModel;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.time.FieldAbsoluteDate;
  import org.orekit.utils.FieldAngularCoordinates;
  import org.orekit.utils.ParameterDriver;
  import org.orekit.utils.TimeStampedFieldAngularCoordinates;
  
  /** Converter for states and parameters arrays.
   * @author Luc Maisonobe
   * @author Bryan Cazabonne
   * @since 10.2
   */
  class DSSTGradientConverter extends AbstractGradientConverter {
  
      /** Fixed dimension of the state. */
      private static final int FREE_STATE_PARAMETERS = 6;
  
      /** States with various number of additional parameters for force models. */
      private final List<FieldSpacecraftState<Gradient>> gStates;
  
      /** Simple constructor.
       * @param state regular state
       * @param provider provider to use if attitude needs to be recomputed
       */
      DSSTGradientConverter(final SpacecraftState state, final AttitudeProvider provider) {
  
          super(FREE_STATE_PARAMETERS);
  
          // equinoctial parameters always has derivatives
          final Gradient sma  = Gradient.variable(FREE_STATE_PARAMETERS, 0, state.getA());
          final Gradient ex   = Gradient.variable(FREE_STATE_PARAMETERS, 1, state.getEquinoctialEx());
          final Gradient ey   = Gradient.variable(FREE_STATE_PARAMETERS, 2, state.getEquinoctialEy());
          final Gradient hx   = Gradient.variable(FREE_STATE_PARAMETERS, 3, state.getHx());
          final Gradient hy   = Gradient.variable(FREE_STATE_PARAMETERS, 4, state.getHy());
          final Gradient l    = Gradient.variable(FREE_STATE_PARAMETERS, 5, state.getLM());
  
          final Gradient gMu = Gradient.constant(FREE_STATE_PARAMETERS, state.getMu());
  
          // date
          final AbsoluteDate date = state.getDate();
          final FieldAbsoluteDate<Gradient> dateField = new FieldAbsoluteDate<>(sma.getField(), date);
  
          // mass never has derivatives
          final Gradient gM = Gradient.constant(FREE_STATE_PARAMETERS, state.getMass());
  
          final FieldOrbit<Gradient> gOrbit =
                          new FieldEquinoctialOrbit<>(sma, ex, ey, hx, hy, l,
                                                      PositionAngle.MEAN,
                                                      state.getFrame(),
                                                      dateField,
                                                      gMu);
  
          final FieldAttitude<Gradient> gAttitude;
          // compute attitude partial derivatives
          gAttitude = provider.getAttitude(gOrbit, gOrbit.getDate(), gOrbit.getFrame());
  
          // initialize the list with the state having 0 force model parameters
          gStates = new ArrayList<>();
          gStates.add(new FieldSpacecraftState<>(gOrbit, gAttitude, gM));
  
      }
  
      /** Get the state with the number of parameters consistent with force model.
       * @param forceModel force model
       * @return state with the number of parameters consistent with force model
       */
      public FieldSpacecraftState<Gradient> getState(final DSSTForceModel forceModel) {
  
         // count the required number of parameters
         int nbParams = 0;
         for (final ParameterDriver driver : forceModel.getParametersDrivers()) {
             if (driver.isSelected()) {
                 ++nbParams;
             }
         }
 
         // 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 = FREE_STATE_PARAMETERS + nbParams;
             final FieldSpacecraftState<Gradient> s0 = gStates.get(0);
 
             final FieldAbsoluteDate<Gradient> date = new FieldAbsoluteDate<>(GradientField.getField(freeParameters),
                                                                              s0.getDate().toAbsoluteDate());
             // orbit
             final FieldOrbit<Gradient> gOrbit =
                             new FieldEquinoctialOrbit<>(extend(s0.getA(),             freeParameters),
                                                         extend(s0.getEquinoctialEx(), freeParameters),
                                                         extend(s0.getEquinoctialEy(), freeParameters),
                                                         extend(s0.getHx(),            freeParameters),
                                                         extend(s0.getHy(),            freeParameters),
                                                         extend(s0.getLM(),            freeParameters),
                                                         PositionAngle.MEAN,
                                                         s0.getFrame(), date,
                                                         extend(s0.getMu(),            freeParameters));
 
             // attitude
             final FieldAngularCoordinates<Gradient> ac0 = s0.getAttitude().getOrientation();
             final FieldAttitude<Gradient> gAttitude =
                             new FieldAttitude<>(s0.getAttitude().getReferenceFrame(),
                                                 new TimeStampedFieldAngularCoordinates<>(gOrbit.getDate(),
                                                                                          extend(ac0.getRotation(),             freeParameters),
                                                                                          extend(ac0.getRotationRate(),         freeParameters),
                                                                                          extend(ac0.getRotationAcceleration(), freeParameters)));
 
             // mass
             final Gradient gM = extend(s0.getMass(), freeParameters);
 
             gStates.set(nbParams, new FieldSpacecraftState<>(gOrbit, gAttitude, gM));
 
         }
 
         return gStates.get(nbParams);
 
     }
 
     /** Get the force model parameters.
      * @param state state as returned by {@link #getState(DSSTForceModel)}
      * @param forceModel force model associated with the parameters
      * @return force model parameters
      */
     public Gradient[] getParameters(final FieldSpacecraftState<Gradient> state,
                                     final DSSTForceModel forceModel) {
         final int freeParameters = state.getA().getFreeParameters();
         final List<ParameterDriver> drivers = forceModel.getParametersDrivers();
         final Gradient[] parameters = new Gradient[drivers.size()];
         int index = FREE_STATE_PARAMETERS;
         int i = 0;
         for (ParameterDriver driver : drivers) {
             parameters[i++] = driver.isSelected() ?
                               Gradient.variable(freeParameters, index++, driver.getValue()) :
                               Gradient.constant(freeParameters, driver.getValue());
         }
         return parameters;
     }
 
 }