/* Copyright 2020-2025 Exotrail
    * 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.conversion.averaging.converters;
  
  import org.orekit.forces.gravity.potential.UnnormalizedSphericalHarmonicsProvider;
  import org.orekit.orbits.Orbit;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.propagation.semianalytical.dsst.DSSTPropagator;
  import org.orekit.propagation.semianalytical.dsst.forces.DSSTForceModel;
  import org.orekit.propagation.conversion.averaging.DSST6X0OrbitalState;
  import org.orekit.propagation.conversion.averaging.elements.AveragedEquinoctialWithMeanAngle;
  
  import java.util.Collection;
  
  /**
   * Class for osculating-to-averaged conversion according to DSST theory, using 6 zonal harmonics as
   * the only perturbations.
   *
   * @author Romain Serra
   * @see DSSTPropagator
   * @see DSST6X0OrbitalState
   * @since 12.1
   */
  public class OsculatingToDSST6X0Converter
          extends FixedPointOsculatingToAveragedConverter<DSST6X0OrbitalState> {
  
      /** Spherical harmonics provider. */
      private final UnnormalizedSphericalHarmonicsProvider harmonicsProvider;
  
      /**
       * Constructor with default parameters for fixed-point algorithm.
       * @param harmonicsProvider unnormalized provider
       */
      public OsculatingToDSST6X0Converter(final UnnormalizedSphericalHarmonicsProvider harmonicsProvider) {
          this(DEFAULT_EPSILON, DEFAULT_MAX_ITERATIONS, harmonicsProvider);
      }
  
      /**
       * Constructor.
       * @param epsilon convergence threshold
       * @param maxIterations maximum number of iterations
       * @param harmonicsProvider unnormalized provider
       */
      public OsculatingToDSST6X0Converter(final double epsilon, final int maxIterations,
                                          final UnnormalizedSphericalHarmonicsProvider harmonicsProvider) {
          super(epsilon, maxIterations);
          this.harmonicsProvider = harmonicsProvider;
      }
  
      /** {@inheritDoc} */
      @Override
      public DSST6X0OrbitalState convertToAveraged(final Orbit osculatingOrbit) {
          final Orbit averagedOrbit = createAveragedOrbit(osculatingOrbit);
          final AveragedEquinoctialWithMeanAngle elements = buildElements(averagedOrbit);
          return new DSST6X0OrbitalState(averagedOrbit.getDate(), elements,
                  averagedOrbit.getFrame(), harmonicsProvider);
      }
  
      /**
       * Build averaged orbit.
       * @param osculatingOrbit osculating orbit
       * @return averaged orbit in DSST sense.
       */
      private Orbit createAveragedOrbit(final Orbit osculatingOrbit) {
          final Collection<DSSTForceModel> forceModels = DSST6X0OrbitalState
                  .createForces(harmonicsProvider);
          final SpacecraftState osculatingState = new SpacecraftState(osculatingOrbit);
          final SpacecraftState averagedState = DSSTPropagator.computeMeanState(osculatingState,
                  null, forceModels, getEpsilon(), getMaxIterations());
          return averagedState.getOrbit();
      }
  
      /**
       * Build averaged orbital elements from orbit.
       * @param averagedOrbit averaged orbit
       * @return orbital elements
       */
      private AveragedEquinoctialWithMeanAngle buildElements(final Orbit averagedOrbit) {
          return new AveragedEquinoctialWithMeanAngle(averagedOrbit.getA(),
                  averagedOrbit.getEquinoctialEx(), averagedOrbit.getEquinoctialEy(),
                  averagedOrbit.getHx(), averagedOrbit.getHy(), averagedOrbit.getLM());
      }
  
  }