/* Copyright 2024-2025 The Johns Hopkins University Applied Physics Laboratory
    * 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.
    * ADS 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.iirv;
  
  import org.orekit.annotation.DefaultDataContext;
  import org.orekit.files.general.EphemerisFile;
  import org.orekit.frames.Frame;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.utils.CartesianDerivativesFilter;
  import org.orekit.utils.Constants;
  import org.orekit.utils.TimeStampedPVCoordinates;
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  
  /**
   * Ephemeris segment from an IIRV file. Each IIRV file (i.e. {@link IIRVMessage}) is defined as containing only one
   * {@link IIRVSegment}.
   *
   * @author Nick LaFarge
   * @since 13.0
   */
  public class IIRVSegment implements EphemerisFile.EphemerisSegment<TimeStampedPVCoordinates> {
  
      /** Gravitational parameter (m^3/s^2). */
      private final double mu;
  
      /** Number of samples to use in interpolation. */
      private final int interpolationSamples;
  
      /** Cartesian derivatives filter: IIRV always contains position & velocity data. */
      private final CartesianDerivativesFilter cartesianDerivativesFilter;
  
      /** Year of the first vector in the file (day of year, but not year itself, is embedded within an IIRV message). */
      private final int startYear;
  
      /** IIRV message consisting of sequential {@link IIRVVector} instances, sorted by {@link org.orekit.files.iirv.terms.SequenceNumberTerm}. */
      private final IIRVMessage iirvMessage;
  
      /**
       * Constructs a {@link IIRVSegment} instance  with default values.
       * <p>
       * Default gravitational parameter is {@link Constants#IERS96_EARTH_MU}. Default number of
       * interpolation samples is 7.
       *
       * @param startYear   Year associated with the beginning of the IIRV message
       * @param iirvMessage IIRV message consisting of sequential {@link IIRVVector} instances, sorted by
       *                    {@link org.orekit.files.iirv.terms.SequenceNumberTerm}.
       */
      public IIRVSegment(final int startYear, final IIRVMessage iirvMessage) {
          this(Constants.IERS96_EARTH_MU, 7, startYear, iirvMessage);
      }
  
      /**
       * Constructs a {@link IIRVSegment} instance.
       *
       * @param mu                   gravitational parameter (m^3/s^2)
       * @param interpolationSamples number of samples to use in interpolation
       * @param startYear            Year associated with the beginning of the IIRV message
       * @param iirvMessage          IIRV message consisting of sequential {@link IIRVVector} instances, sorted by
       *                             {@link org.orekit.files.iirv.terms.SequenceNumberTerm}.
       */
      public IIRVSegment(final double mu, final int interpolationSamples, final int startYear, final IIRVMessage iirvMessage) {
          this.mu = mu;
          this.interpolationSamples = interpolationSamples;
          this.cartesianDerivativesFilter = CartesianDerivativesFilter.USE_PV;
          this.startYear = startYear;
          this.iirvMessage = iirvMessage;
      }
  
      /** {@inheritDoc} */
      @Override
      public double getMu() {
          return mu;
      }
  
      /** {@inheritDoc} */
      @Override
      @DefaultDataContext
      public Frame getFrame() {
          return iirvMessage.getVectors().get(0).getFrame();
      }
  
      /** {@inheritDoc} */
     @Override
     public int getInterpolationSamples() {
         return interpolationSamples;
     }
 
     /** {@inheritDoc} */
     @Override
     public CartesianDerivativesFilter getAvailableDerivatives() {
         return cartesianDerivativesFilter;
     }
 
     /** {@inheritDoc} */
     @Override
     public AbsoluteDate getStart() {
         return getCoordinates().get(0).getDate();
     }
 
     /** {@inheritDoc} */
     @Override
     public AbsoluteDate getStop() {
         return getCoordinates().get(getCoordinates().size() - 1).getDate();
     }
 
     /** {@inheritDoc} */
     @Override
     public List<TimeStampedPVCoordinates> getCoordinates() {
         int year = startYear;
         final List<IIRVVector> iirvVectors = iirvMessage.getVectors();
 
         final ArrayList<TimeStampedPVCoordinates> coordinates = new ArrayList<>();
         coordinates.add(iirvVectors.get(0).getTimeStampedPVCoordinates(year));
 
         for (int i = 1; i < iirvVectors.size(); i++) {
             final IIRVVector prev = iirvVectors.get(i - 1);
             final IIRVVector next = iirvVectors.get(i);
 
             // Increase the year counter if the previous day is greater than the current day
             if (prev.getDayOfYear().value() > next.getDayOfYear().value()) {
                 year++;
             }
             coordinates.add(next.getTimeStampedPVCoordinates(year));
         }
         return Collections.unmodifiableList(coordinates);
     }
 
     /**
      * Gets the IIRV message for this segment.
      *
      * @return IIRV message for this segment
      */
     public IIRVMessage getIIRVMessage() {
         return iirvMessage;
     }
 
     /**
      * Gets the start year for this segment.
      *
      * @return start year for this segment.
      */
     public int getStartYear() {
         return startYear;
     }
 }