/* Copyright 2002-2022 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.numerical;
  
  import org.hipparchus.Field;
  import org.hipparchus.analysis.differentiation.Gradient;
  import org.hipparchus.analysis.differentiation.GradientField;
  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.FieldCartesianOrbit;
  import org.orekit.orbits.FieldOrbit;
  import org.orekit.propagation.FieldSpacecraftState;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.propagation.integration.AbstractGradientConverter;
  import org.orekit.utils.TimeStampedFieldPVCoordinates;
  
  /** Converter for states and parameters arrays.
   * @author Luc Maisonobe
   * @since 10.2
   */
  class NumericalGradientConverter extends AbstractGradientConverter {
  
      /** Simple constructor.
       * @param state regular state
       * @param freeStateParameters number of free parameters, either 3 (position) or 6 (position-velocity)
       * @param provider provider to use if attitude needs to be recomputed
       */
      NumericalGradientConverter(final SpacecraftState state, final int freeStateParameters,
                                 final AttitudeProvider provider) {
  
          super(freeStateParameters);
  
          // Derivative field
          final Field<Gradient> field =  GradientField.getField(freeStateParameters);
  
          // position always has derivatives
          final Vector3D pos = state.getPVCoordinates().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<>(Gradient.constant(freeStateParameters, vel.getX()),
                                         Gradient.constant(freeStateParameters, vel.getY()),
                                         Gradient.constant(freeStateParameters, vel.getZ()));
          }
  
          // acceleration never has derivatives
          final Vector3D acc = state.getPVCoordinates().getAcceleration();
          final FieldVector3D<Gradient> accG = new FieldVector3D<>(Gradient.constant(freeStateParameters, acc.getX()),
                                                                   Gradient.constant(freeStateParameters, acc.getY()),
                                                                   Gradient.constant(freeStateParameters, acc.getZ()));
  
          // mass never has derivatives
          final Gradient gM = Gradient.constant(freeStateParameters, state.getMass());
  
          final Gradient gMu = Gradient.constant(freeStateParameters, state.getMu());
  
          final FieldOrbit<Gradient> gOrbit =
                          new FieldCartesianOrbit<>(new TimeStampedFieldPVCoordinates<>(state.getDate(), posG, velG, accG),
                                                    state.getFrame(), gMu);
  
          final FieldAttitude<Gradient> gAttitude;
          if (freeStateParameters > 3) {
              // compute attitude partial derivatives with respect to position/velocity
              gAttitude = provider.getAttitude(gOrbit, gOrbit.getDate(), gOrbit.getFrame());
          } else {
              // force model does not depend on attitude, don't bother recomputing it
              gAttitude = new FieldAttitude<>(field, state.getAttitude());
          }
  
          // initialize the list with the state having 0 force model parameters
          initStates(new FieldSpacecraftState<>(gOrbit, gAttitude, gM));
  
      }
  
 }