/* Copyright 2002-2024 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.models.earth.tessellation;
  
  import java.util.ArrayList;
  import java.util.List;
  
  import org.hipparchus.util.Pair;
  import org.orekit.bodies.GeodeticPoint;
  import org.orekit.bodies.OneAxisEllipsoid;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.propagation.sampling.OrekitFixedStepHandler;
  import org.orekit.utils.TimeStampedPVCoordinates;
  
  /** Sampler for half track span.
   * @since 7.1
   * @see AlongTrackAiming
   * @author Luc Maisonobe
   */
  class HalfTrackSampler implements OrekitFixedStepHandler {
  
      /** Ellipsoid over which track is sampled. */
      private final OneAxisEllipsoid ellipsoid;
  
      /** Half track sample. */
      private final List<Pair<GeodeticPoint, TimeStampedPVCoordinates>> halfTrack;
  
      /** Simple constructor.
       * @param ellipsoid ellipsoid over which track is sampled
       */
      HalfTrackSampler(final OneAxisEllipsoid ellipsoid) {
          this.ellipsoid = ellipsoid;
          this.halfTrack = new ArrayList<Pair<GeodeticPoint, TimeStampedPVCoordinates>>();
      }
  
      /** Get half track sample.
       * @return half track sample
       */
      public List<Pair<GeodeticPoint, TimeStampedPVCoordinates>> getHalfTrack() {
          return halfTrack;
      }
  
      /** {@inheritDoc} */
      @Override
      public void handleStep(final SpacecraftState currentState) {
  
          // find the sliding ground point below spacecraft
          final TimeStampedPVCoordinates pv       = currentState.getPVCoordinates(ellipsoid.getBodyFrame());
          final TimeStampedPVCoordinates groundPV = ellipsoid.projectToGround(pv, ellipsoid.getBodyFrame());
  
          // geodetic coordinates
          final GeodeticPoint gp =
                          ellipsoid.transform(groundPV.getPosition(), ellipsoid.getBodyFrame(), currentState.getDate());
  
          halfTrack.add(new Pair<GeodeticPoint, TimeStampedPVCoordinates>(gp, groundPV));
  
      }
  
  }