/* Copyright 2002-2021 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,
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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.Field;
  import org.hipparchus.CalculusFieldElement;
  import org.hipparchus.geometry.euclidean.threed.Vector3D;
  import org.hipparchus.ode.events.Action;
  import org.hipparchus.util.FastMath;
  import org.orekit.propagation.FieldSpacecraftState;
  import org.orekit.propagation.events.handlers.FieldEventHandler;
  import org.orekit.propagation.events.handlers.FieldStopOnIncreasing;
  import org.orekit.utils.PVCoordinatesProvider;
  
  /** Finder for satellite eclipse related events.
   * <p>This class finds eclipse events, i.e. satellite within umbra (total
   * eclipse) or penumbra (partial eclipse).</p>
   * <p>The default implementation behavior is to {@link Action#CONTINUE continue}
   * propagation when entering the eclipse and to {@link Action#STOP stop} propagation
   * when exiting the eclipse. This can be changed by calling {@link
   * #withHandler(FieldEventHandler)} after construction.</p>
   * @see org.orekit.propagation.FieldPropagator#addEventDetector(FieldEventDetector)
   * @author Pascal Parraud
   */
  public class FieldEclipseDetector<T extends CalculusFieldElement<T>> extends FieldAbstractDetector<FieldEclipseDetector<T>, T> {
  
  
      /** Occulting body. */
      private final PVCoordinatesProvider occulting;
  
      /** Occulting body radius (m). */
      private final double occultingRadius;
  
      /** Occulted body. */
      private final PVCoordinatesProvider occulted;
  
      /** Occulted body radius (m). */
      private final double occultedRadius;
  
      /** Umbra, if true, or penumbra, if false, detection flag. */
      private boolean totalEclipse;
  
      /** Build a new eclipse detector.
       * <p>The new instance is a total eclipse (umbra) detector with default
       * values for maximal checking interval ({@link #DEFAULT_MAXCHECK})
       * and convergence threshold ({@link #DEFAULT_THRESHOLD}).</p>
       * @param occulted the body to be occulted
       * @param occultedRadius the radius of the body to be occulted (m)
       * @param occulting the occulting body
       * @param occultingRadius the occulting body radius (m)
       * @param field field used by default
       */
      public FieldEclipseDetector(final PVCoordinatesProvider occulted,  final double occultedRadius,
                             final PVCoordinatesProvider occulting, final double occultingRadius, final Field<T> field) {
          this(field.getZero().add(DEFAULT_MAXCHECK), field.getZero().add(DEFAULT_THRESHOLD),
               occulted, occultedRadius, occulting, occultingRadius);
      }
  
      /** Build a new eclipse detector.
       * <p>The new instance is a total eclipse (umbra) detector with default
       * value for convergence threshold ({@link #DEFAULT_THRESHOLD}).</p>
       * <p>The maximal interval between eclipse checks should be smaller than
       * the half duration of the minimal pass to handle, otherwise some short
       * passes could be missed.</p>
       * @param maxCheck maximal checking interval (s)
       * @param occulted the body to be occulted
       * @param occultedRadius the radius of the body to be occulted in meters
       * @param occulting the occulting body
       * @param occultingRadius the occulting body radius in meters
       */
      public FieldEclipseDetector(final T maxCheck,
                             final PVCoordinatesProvider occulted,  final double occultedRadius,
                             final PVCoordinatesProvider occulting, final double occultingRadius) {
          this(maxCheck, maxCheck.getField().getZero().add(DEFAULT_THRESHOLD),
               occulted, occultedRadius, occulting, occultingRadius);
      }
  
      /** Build a new eclipse detector.
       * <p>The new instance is a total eclipse (umbra) detector.</p>
       * <p>The maximal interval between eclipse checks should be smaller than
       * the half duration of the minimal pass to handle, otherwise some short
       * passes could be missed.</p>
       * @param maxCheck maximal checking interval (s)
       * @param threshold convergence threshold (s)
       * @param occulted the body to be occulted
      * @param occultedRadius the radius of the body to be occulted in meters
      * @param occulting the occulting body
      * @param occultingRadius the occulting body radius in meters
      */
     public FieldEclipseDetector(final T maxCheck, final T threshold,
                            final PVCoordinatesProvider occulted,  final double occultedRadius,
                            final PVCoordinatesProvider occulting, final double occultingRadius) {
         this(maxCheck, threshold, DEFAULT_MAX_ITER, new FieldStopOnIncreasing<FieldEclipseDetector<T>, T>(),
              occulted, occultedRadius, occulting, occultingRadius, true);
     }
 
     /** Private constructor with full parameters.
      * <p>
      * This constructor is private as users are expected to use the builder
      * API with the various {@code withXxx()} methods to set up the instance
      * in a readable manner without using a huge amount of parameters.
      * </p>
      * @param maxCheck maximum checking interval (s)
      * @param threshold convergence threshold (s)
      * @param maxIter maximum number of iterations in the event time search
      * @param handler event handler to call at event occurrences
      * @param occulted the body to be occulted
      * @param occultedRadius the radius of the body to be occulted in meters
      * @param occulting the occulting body
      * @param occultingRadius the occulting body radius in meters
      * @param totalEclipse umbra (true) or penumbra (false) detection flag
      * @since 6.1
      */
     private FieldEclipseDetector(final T maxCheck, final T threshold,
                             final int maxIter, final FieldEventHandler<? super FieldEclipseDetector<T>, T> handler,
                             final PVCoordinatesProvider occulted,  final double occultedRadius,
                             final PVCoordinatesProvider occulting, final double occultingRadius,
                             final boolean totalEclipse) {
         super(maxCheck, threshold, maxIter, handler);
         this.occulted        = occulted;
         this.occultedRadius  = FastMath.abs(occultedRadius);
         this.occulting       = occulting;
         this.occultingRadius = FastMath.abs(occultingRadius);
         this.totalEclipse    = totalEclipse;
     }
 
     /** {@inheritDoc} */
     @Override
     protected FieldEclipseDetector<T> create(final T newMaxCheck, final T newThreshold,
                                      final int nawMaxIter, final FieldEventHandler<? super FieldEclipseDetector<T>, T> newHandler) {
         return new FieldEclipseDetector<>(newMaxCheck, newThreshold, nawMaxIter, newHandler,
                                           occulted, occultedRadius, occulting, occultingRadius, totalEclipse);
     }
 
     /**
      * Setup the detector to full umbra detection.
      * <p>
      * This will override a penumbra/umbra flag if it has been configured previously.
      * </p>
      * @return a new detector with updated configuration (the instance is not changed)
      * @see #withPenumbra()
      * @since 6.1
      */
     public FieldEclipseDetector<T> withUmbra() {
         return new FieldEclipseDetector<>(getMaxCheckInterval(), getThreshold(), getMaxIterationCount(), getHandler(),
                                           occulted, occultedRadius, occulting, occultingRadius,
                                           true);
     }
 
     /**
      * Setup the detector to penumbra detection.
      * <p>
      * This will override a penumbra/umbra flag if it has been configured previously.
      * </p>
      * @return a new detector with updated configuration (the instance is not changed)
      * @see #withUmbra()
      * @since 6.1
      */
     public FieldEclipseDetector<T> withPenumbra() {
         return new FieldEclipseDetector<>(getMaxCheckInterval(), getThreshold(), getMaxIterationCount(), getHandler(),
                                           occulted, occultedRadius, occulting, occultingRadius,
                                           false);
     }
 
     /** Get the occulting body.
      * @return the occulting body
      */
     public PVCoordinatesProvider getOcculting() {
         return occulting;
     }
 
     /** Get the occulting body radius (m).
      * @return the occulting body radius
      */
     public double getOccultingRadius() {
         return occultingRadius;
     }
 
     /** Get the occulted body.
      * @return the occulted body
      */
     public PVCoordinatesProvider getOcculted() {
         return occulted;
     }
 
     /** Get the occulted body radius (m).
      * @return the occulted body radius
      */
     public double getOccultedRadius() {
         return occultedRadius;
     }
 
     /** Get the total eclipse detection flag.
      * @return the total eclipse detection flag (true for umbra events detection,
      * false for penumbra events detection)
      */
     public boolean getTotalEclipse() {
         return totalEclipse;
     }
 
     /** Compute the value of the switching function.
      * This function becomes negative when entering the region of shadow
      * and positive when exiting.
      * @param s the current state information: date, kinematics, attitude
      * @return value of the switching function
      */
     public T g(final FieldSpacecraftState<T> s) {
         final T        zero = s.getOrbit().getA().getField().getZero();
         final Vector3D pted = occulted.getPVCoordinates(s.getDate().toAbsoluteDate(), s.getFrame()).getPosition();
         final Vector3D ping = occulting.getPVCoordinates(s.getDate().toAbsoluteDate(), s.getFrame()).getPosition();
         final Vector3D psat = s.toSpacecraftState().getPVCoordinates().getPosition();
         final Vector3D ps   = pted.subtract(psat);
         final Vector3D po   = ping.subtract(psat);
         final double angle  = Vector3D.angle(ps, po);
         final double rs     = FastMath.asin(occultedRadius / ps.getNorm());
         if (Double.isNaN(rs)) {
             return zero.getPi();
         }
         final double ro     = FastMath.asin(occultingRadius / po.getNorm());
         if (Double.isNaN(ro)) {
             return zero.getPi().negate();
         }
         return totalEclipse ? (zero.add(angle - ro + rs)) : (zero.add(angle - ro - rs));
     }
 
 }