/* 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.CircularOrbit;
  import org.orekit.orbits.Orbit;
  import org.orekit.propagation.analytical.EcksteinHechlerPropagator;
  import org.orekit.propagation.conversion.averaging.EcksteinHechlerOrbitalState;
  import org.orekit.propagation.conversion.averaging.elements.AveragedCircularWithMeanAngle;
  
  /**
   * Class for osculating-to-averaged conversion according to Eckstein-Hechler theory.
   *
   * @author Romain Serra
   * @see EcksteinHechlerPropagator
   * @see EcksteinHechlerOrbitalState
   * @since 12.1
   */
  public class OsculatingToEcksteinHechlerConverter
          extends FixedPointOsculatingToAveragedConverter<EcksteinHechlerOrbitalState> {
  
      /** Order for spherical harmonics. */
      private static final int HARMONICS_ORDER = 0;
  
      /** Spherical harmonics provider. */
      private final UnnormalizedSphericalHarmonicsProvider harmonicsProvider;
  
      /**
       * Constructor with default parameters for fixed-point algorithm.
       * @param harmonicsProvider unnormalized provider
       */
      public OsculatingToEcksteinHechlerConverter(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 OsculatingToEcksteinHechlerConverter(final double epsilon, final int maxIterations,
                                                  final UnnormalizedSphericalHarmonicsProvider harmonicsProvider) {
          super(epsilon, maxIterations);
          this.harmonicsProvider = harmonicsProvider;
      }
  
      /** {@inheritDoc} */
      @Override
      public EcksteinHechlerOrbitalState convertToAveraged(final Orbit osculatingOrbit) {
          final CircularOrbit averagedOrbit = createAveragedOrbit(osculatingOrbit);
          final AveragedCircularWithMeanAngle elements = buildElements(averagedOrbit);
          return new EcksteinHechlerOrbitalState(averagedOrbit.getDate(), elements,
                  averagedOrbit.getFrame(), harmonicsProvider);
      }
  
      /**
       * Build averaged orbit.
       * @param osculatingOrbit osculating orbit
       * @return averaged Circular orbit in Eckstein-Hechler sense.
       */
      private CircularOrbit createAveragedOrbit(final Orbit osculatingOrbit) {
          final UnnormalizedSphericalHarmonicsProvider.UnnormalizedSphericalHarmonics harmonics =
                  harmonicsProvider.onDate(osculatingOrbit.getDate());
          return EcksteinHechlerPropagator.computeMeanOrbit(osculatingOrbit,
                  harmonicsProvider.getAe(), harmonicsProvider.getMu(),
                  harmonics.getUnnormalizedCnm(2, HARMONICS_ORDER),
                  harmonics.getUnnormalizedCnm(3, HARMONICS_ORDER),
                  harmonics.getUnnormalizedCnm(4, HARMONICS_ORDER),
                  harmonics.getUnnormalizedCnm(5, HARMONICS_ORDER),
                  harmonics.getUnnormalizedCnm(6, HARMONICS_ORDER),
                  getEpsilon(), getMaxIterations());
      }
  
      /**
       * Build averaged orbital elements from orbit.
       * @param averagedOrbit averaged orbit
       * @return orbital elements
       */
      private AveragedCircularWithMeanAngle buildElements(final CircularOrbit averagedOrbit) {
          return new AveragedCircularWithMeanAngle(averagedOrbit.getA(),
                  averagedOrbit.getCircularEx(), averagedOrbit.getCircularEy(), averagedOrbit.getI(),
                  averagedOrbit.getRightAscensionOfAscendingNode(), averagedOrbit.getAlphaM());
      }
 
 }