/* Copyright 2022-2025 Luc Maisonobe
    * 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.files.sp3;
  
  import org.hipparchus.analysis.interpolation.HermiteInterpolator;
  import org.orekit.attitudes.AttitudeProvider;
  import org.orekit.attitudes.FrameAlignedProvider;
  import org.orekit.files.general.EphemerisFile;
  import org.orekit.files.general.EphemerisSegmentPropagator;
  import org.orekit.frames.Frame;
  import org.orekit.propagation.BoundedPropagator;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.time.ClockModel;
  import org.orekit.time.ClockOffset;
  import org.orekit.time.SampledClockModel;
  import org.orekit.utils.CartesianDerivativesFilter;
  import org.orekit.utils.SortedListTrimmer;
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  
  /** One segment of an {@link SP3Ephemeris}.
   * @author Thomas Neidhart
   * @author Evan Ward
   * @author Luc Maisonobe
   * @since 12.0
   */
  public class SP3Segment implements EphemerisFile.EphemerisSegment<SP3Coordinate> {
  
      /** Standard gravitational parameter in m³ / s². */
      private final double mu;
  
      /** Reference frame. */
      private final Frame frame;
  
      /** Number of points to use for interpolation. */
      private final int interpolationSamples;
  
      /** Available derivatives. */
      private final CartesianDerivativesFilter filter;
  
      /** Ephemeris Data. */
      private final List<SP3Coordinate> coordinates;
  
      /** Simple constructor.
       * @param mu standard gravitational parameter to use for creating
       * {@link org.orekit.orbits.Orbit Orbits} from the ephemeris data.
       * @param frame reference frame
       * @param interpolationSamples number of points to use for interpolation
       * @param filter available derivatives
       */
      public SP3Segment(final double mu, final Frame frame,
                        final int interpolationSamples, final CartesianDerivativesFilter filter) {
          this.mu                   = mu;
          this.frame                = frame;
          this.interpolationSamples = interpolationSamples;
          this.filter               = filter;
          this.coordinates          = new ArrayList<>();
      }
  
      /** Extract the clock model.
       * <p>
       * If some clock or clock rate are present in the SP3 files as default values (999999.999999), then they
       * filtered out here when building the clock model, so interpolation will work if at least there are
       * some remaining regular values.
       * </p>
       * @return extracted clock model
       * @since 12.1
       */
      public ClockModel extractClockModel() {
          final List<ClockOffset> sample = new ArrayList<>(coordinates.size());
          coordinates.forEach(c -> {
              final AbsoluteDate date   = c.getDate();
              final double       offset = c.getClockCorrection();
              if (!Double.isNaN(offset)) {
                  final double rate = filter.getMaxOrder() > 0 ? c.getClockRateChange() : Double.NaN;
                  sample.add(new ClockOffset(date, offset, rate, Double.NaN));
              }
          });
          return new SampledClockModel(sample, interpolationSamples);
      }
  
      /** {@inheritDoc} */
     @Override
     public double getMu() {
         return mu;
     }
 
     /** {@inheritDoc} */
     @Override
     public AbsoluteDate getStart() {
         return coordinates.get(0).getDate();
     }
 
     /** {@inheritDoc} */
     @Override
     public AbsoluteDate getStop() {
         return coordinates.get(coordinates.size() - 1).getDate();
     }
 
     /** {@inheritDoc} */
     @Override
     public Frame getFrame() {
         return frame;
     }
 
     /** {@inheritDoc} */
     @Override
     public int getInterpolationSamples() {
         return interpolationSamples;
     }
 
     /** {@inheritDoc} */
     @Override
     public CartesianDerivativesFilter getAvailableDerivatives() {
         return filter;
     }
 
     /** {@inheritDoc} */
     @Override
     public List<SP3Coordinate> getCoordinates() {
         return Collections.unmodifiableList(this.coordinates);
     }
 
     /** Adds a new P/V coordinate.
      * @param coord the P/V coordinate of the satellite
      */
     public void addCoordinate(final SP3Coordinate coord) {
         coordinates.add(coord);
     }
 
     /** {@inheritDoc} */
     @Override
     public BoundedPropagator getPropagator() {
         return new PropagatorWithClock(new FrameAlignedProvider(getInertialFrame()));
     }
 
     /** {@inheritDoc} */
     @Override
     public BoundedPropagator getPropagator(final AttitudeProvider attitudeProvider) {
         return new PropagatorWithClock(attitudeProvider);
     }
 
     /** Propagator including clock.
      * @since 12.1
      */
     private class PropagatorWithClock extends EphemerisSegmentPropagator<SP3Coordinate> {
 
         /** Trimmer for coordinates list. */
         private final SortedListTrimmer trimmer;
 
         /** Simple constructor.
          * @param attitudeProvider attitude porovider
          */
         PropagatorWithClock(final AttitudeProvider attitudeProvider) {
             super(SP3Segment.this, attitudeProvider);
             this.trimmer = new SortedListTrimmer(getInterpolationSamples());
         }
 
         /** {@inheritDoc} */
         @Override
         public SpacecraftState updateAdditionalData(final SpacecraftState original) {
 
             final HermiteInterpolator interpolator = new HermiteInterpolator();
 
             // Fill interpolator with sample
             trimmer.
                 getNeighborsSubList(original.getDate(), coordinates).
                 forEach(c -> {
                     final double deltaT = c.getDate().durationFrom(original.getDate());
                     if (filter.getMaxOrder() < 1) {
                         // we use only clock offset
                         interpolator.addSamplePoint(deltaT,
                                                     new double[] { c.getClockCorrection() });
                     } else {
                         // we use both clock offset and clock rate
                         interpolator.addSamplePoint(deltaT,
                                                     new double[] { c.getClockCorrection() },
                                                     new double[] { c.getClockRateChange() });
                     }
                 });
 
             // perform interpolation (we get derivatives even if we used only clock offset)
             final double[][] derivatives = interpolator.derivatives(0.0, 1);
 
             // add the clock offset and its first derivative
             return super.updateAdditionalData(original).
                 addAdditionalData(SP3Utils.CLOCK_ADDITIONAL_STATE, derivatives[0]).
                 addAdditionalStateDerivative(SP3Utils.CLOCK_ADDITIONAL_STATE, derivatives[1]);
 
         }
 
     }
 
 }