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    * contributor license agreements.  See the NOTICE file distributed with
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    * 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
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    *
    *   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,
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   * See the License for the specific language governing permissions and
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  package org.orekit.propagation.events;
  
  import org.hipparchus.util.FastMath;
  import org.junit.jupiter.api.Assertions;
  import org.junit.jupiter.api.Test;
  import org.mockito.Mockito;
  import org.orekit.Utils;
  import org.orekit.bodies.CelestialBodyFactory;
  import org.orekit.frames.Frame;
  import org.orekit.frames.FramesFactory;
  import org.orekit.orbits.KeplerianOrbit;
  import org.orekit.orbits.Orbit;
  import org.orekit.orbits.PositionAngleType;
  import org.orekit.propagation.Propagator;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.propagation.analytical.KeplerianPropagator;
  import org.orekit.propagation.events.handlers.StopOnEvent;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.utils.PVCoordinatesProvider;
  
  public class ExtremumApproachDetectorTest {
  
      /**
      * Test the detector on a keplerian orbit and detect extremum approach with Earth.
      */
      @Test
      public void testStopPropagationClosestApproachByDefault() {
          // Given
          // Loading Orekit data
          Utils.setDataRoot("regular-data");
  
          // Generating orbit
          final AbsoluteDate initialDate = new AbsoluteDate();
          final Frame frame = FramesFactory.getEME2000();
          final double mu = 398600e9; //m**3/s**2
  
          final double rp = (6378 + 400) * 1000; //m
          final double ra = (6378 + 800) * 1000; //m
  
          final double a = (ra + rp) / 2; //m
          final double e = (ra - rp) / (ra + rp); //m
          final double i = 0; //rad
          final double pa = 0; //rad
          final double raan = 0; //rad
          final double anomaly = FastMath.toRadians(0); //rad
          final Orbit orbit =
                  new KeplerianOrbit(a, e, i, pa, raan, anomaly, PositionAngleType.TRUE, frame, initialDate, mu);
  
          // Will detect extremum approaches with Earth
          final PVCoordinatesProvider earthPVProvider = CelestialBodyFactory.getEarth();
  
          // Initializing detector
          final ExtremumApproachDetector detector = new ExtremumApproachDetector(earthPVProvider);
  
          // Initializing propagator
          final Propagator propagator = new KeplerianPropagator(orbit);
          propagator.addEventDetector(detector);
  
          // When
          final SpacecraftState stateAtEvent =
                  propagator.propagate(initialDate.shiftedBy(orbit.getKeplerianPeriod() * 2));
  
          // Then
          Assertions.assertEquals(stateAtEvent.getDate().durationFrom(initialDate),orbit.getKeplerianPeriod(),1e-9);
  
      }
  
      /**
      * Test the detector on a keplerian orbit and detect extremum approach with Earth.
      */
      @Test
      public void testStopPropagationFarthestApproachWithHandler() {
          
          // Given
          // Loading Orekit data
          Utils.setDataRoot("regular-data");
  
          // Generating orbit
          final AbsoluteDate initialDate = new AbsoluteDate();
          final Frame frame = FramesFactory.getEME2000();
          final double mu = 398600e9; //m**3/s**2
  
          final double rp = (6378 + 400) * 1000; //m
         final double ra = (6378 + 800) * 1000; //m
 
         final double a = (ra + rp) / 2; //m
         final double e = (ra - rp) / (ra + rp); //m
         final double i = 0; //rad
         final double pa = 0; //rad
         final double raan = 0; //rad
         final double anomaly = FastMath.toRadians(0); //rad
         final Orbit orbit =
                 new KeplerianOrbit(a, e, i, pa, raan, anomaly, PositionAngleType.TRUE, frame, initialDate, mu);
 
         // Will detect extremum approaches with Earth
         final PVCoordinatesProvider earthPVProvider = CelestialBodyFactory.getEarth();
 
         // Initializing detector with custom handler
         final ExtremumApproachDetector detector =
                 new ExtremumApproachDetector(earthPVProvider).withHandler(new StopOnEvent());
 
         // Initializing propagator
         final Propagator propagator = new KeplerianPropagator(orbit);
         propagator.addEventDetector(detector);
 
         // When
         final SpacecraftState stateAtEvent =
                 propagator.propagate(initialDate.shiftedBy(orbit.getKeplerianPeriod() * 2));
 
         // Then
         Assertions.assertEquals(stateAtEvent.getDate().durationFrom(initialDate),orbit.getKeplerianPeriod() / 2,1e-7);
 
     }
 
     @Test
     void testSecondaryPVCoordinatesProviderGetter() {
         // Given
         final PVCoordinatesProvider    secondaryPVProvider      = Mockito.mock(PVCoordinatesProvider.class);
         final ExtremumApproachDetector extremumApproachDetector = new ExtremumApproachDetector(secondaryPVProvider);
 
         // When
         final PVCoordinatesProvider returnedSecondaryPVProvider = extremumApproachDetector.getSecondaryPVProvider();
 
         // Then
         Assertions.assertEquals(secondaryPVProvider, returnedSecondaryPVProvider);
     }
 }