/* Contributed in the public domain.
    * 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.frames;
  
  import org.hamcrest.MatcherAssert;
  import org.hamcrest.core.IsInstanceOf;
  import org.hipparchus.geometry.euclidean.threed.Vector3D;
  import org.junit.jupiter.api.Assertions;
  import org.junit.jupiter.api.BeforeAll;
  import org.junit.jupiter.api.Test;
  import org.orekit.Utils;
  import org.orekit.bodies.CelestialBody;
  import org.orekit.bodies.CelestialBodyFactory;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.time.TimeScale;
  import org.orekit.time.TimeScalesFactory;
  import org.orekit.utils.Constants;
  import org.orekit.utils.IERSConventions;
  
  
  /** Unit tests for {@link EclipticProvider}. */
  public class EclipticProviderTest {
  
      /** Set the orekit data to include ephemerides. */
      @BeforeAll
      public static void setUpBefore() {
          Utils.setDataRoot("regular-data");
      }
  
      /**
       * Check the Ecliptic frame defined from IERS mean obliquity equations against the
       * position of Sun and Earth from the JPL 406 ephemerides.
       *
       * @throws Exception on error
       */
      @Test
      public void testAgreementWith406Ephemerides() throws Exception {
          TimeScale utc = TimeScalesFactory.getUTC();
  
          //time spans we have test data sets for.
          checkAlignment(new AbsoluteDate(1969, 5, 27, utc), new AbsoluteDate(1969, 9, 20, utc));
          checkAlignment(new AbsoluteDate(1969, 12, 5, utc), new AbsoluteDate(1970, 4, 1, utc));
          checkAlignment(new AbsoluteDate(1970, 6, 15, utc), new AbsoluteDate(1970, 8, 1, utc));
          checkAlignment(new AbsoluteDate(2002, 12, 16, utc), new AbsoluteDate(2004, 2, 3, utc));
  
          checkAlignment(new AbsoluteDate(1999, 11, 22, utc), new AbsoluteDate(2000, 5, 21, utc));
      }
  
      /**
       * Check alignment of ecliptic +z with Earth-Moon barycenter angular momentum. Angular
       * difference will be checked every month.
       *
       * @param start start date of check.
       * @param end   en date of check.
       */
      private void checkAlignment(AbsoluteDate start, AbsoluteDate end) {
          //setup
          CelestialBody sun = CelestialBodyFactory.getSun();
          CelestialBody emb = CelestialBodyFactory.getEarthMoonBarycenter();
          Frame heliocentric = sun.getInertiallyOrientedFrame();
          //subject under test
          Frame ecliptic = FramesFactory.getEcliptic(IERSConventions.IERS_2010);
  
          //verify
          //precise definition is +z is parallel to Earth-Moon barycenter's angular momentum
          //over date range of ephemeris, a season at a time
          double preciseTol = 0.50 * Constants.ARC_SECONDS_TO_RADIANS;
          for (AbsoluteDate date = start;
               date.compareTo(end) < 0;
               date = date.shiftedBy(Constants.JULIAN_YEAR / 12.0)) {
  
              Transform heliocentricToEcliptic = heliocentric.getTransformTo(ecliptic, date);
              Vector3D momentum = emb.getPVCoordinates(date, heliocentric).getMomentum();
              Vector3D actual = heliocentricToEcliptic.transformVector(momentum);
              double angle = Vector3D.angle(
                      Vector3D.PLUS_K,
                      actual
              );
              Assertions.assertEquals(0, angle, preciseTol,"Agrees with ephemerides to within " + preciseTol);
  
          }
  
      }
  
      /**
      * Check frame has the right name.
      */
     @Test
     public void testGetName() {
         Assertions.assertEquals("Ecliptic/1996",
                             FramesFactory.getEcliptic(IERSConventions.IERS_1996).getName());
         Assertions.assertEquals("Ecliptic/2003",
                             FramesFactory.getEcliptic(IERSConventions.IERS_2003).getName());
         Assertions.assertEquals("Ecliptic/2010",
                             FramesFactory.getEcliptic(IERSConventions.IERS_2010).getName());
     }
 
     /**
      * Check the parent frame is MOD.
      */
     @Test
     public void testGetParent() {
         //setup
         Frame frame = FramesFactory.getEcliptic(IERSConventions.IERS_2003);
 
         //action + verify
         MatcherAssert.assertThat(frame.getParent().getTransformProvider(),
                           IsInstanceOf.instanceOf(MODProvider.class));
     }
 
 }