/* 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.propagation.events;
  
  
  import java.io.Serializable;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collection;
  import java.util.Comparator;
  import java.util.List;
  import java.util.NoSuchElementException;
  
  import org.hipparchus.CalculusFieldElement;
  import org.hipparchus.util.FastMath;
  import org.orekit.propagation.FieldSpacecraftState;
  import org.orekit.propagation.events.handlers.FieldContinueOnEvent;
  import org.orekit.propagation.events.handlers.FieldEventHandler;
  import org.orekit.propagation.events.intervals.FieldAdaptableInterval;
  import org.orekit.time.FieldAbsoluteDate;
  
  /**
   * This class provides AND and OR operations for event detectors. This class treats
   * positive values of the g function as true and negative values as false.
   *
   * <p> One example for an imaging satellite might be to only detect events when a
   * satellite is overhead (elevation &gt; 0) AND when the ground point is sunlit (Sun
   * elevation &gt; 0). Another slightly contrived example using the OR operator would be to
   * detect access to a set of ground stations and only report events when the satellite
   * enters or leaves the field of view of the set, but not hand-offs between the ground
   * stations.
   *
   * <p> For the FieldBooleanDetector is important that the sign of the g function of the
   * underlying event detector is not arbitrary, but has a semantic meaning, e.g. in or out,
   * true or false. This class works well with event detectors that detect entry to or exit
   * from a region, e.g. {@link FieldEclipseDetector}, {@link FieldElevationDetector}, {@link
   * FieldLatitudeCrossingDetector}. Using this detector with detectors that are not based on
   * entry to or exit from a region, e.g. {@link FieldDateDetector}, will likely lead to
   * unexpected results. To apply conditions to this latter type of event detectors a
   * {@link FieldEventEnablingPredicateFilter} is usually more appropriate.
   *
   * @param <T> type of the field elements
   * @since 12.0
   * @author Evan Ward
   * @author luc Luc Maisonobe
   * @see #andCombine(Collection)
   * @see #orCombine(Collection)
   * @see #notCombine(FieldEventDetector)
   * @see EventEnablingPredicateFilter
   * @see EventSlopeFilter
   */
  public class FieldBooleanDetector<T extends CalculusFieldElement<T>> extends FieldAbstractDetector<FieldBooleanDetector<T>, T> {
  
      /** Original detectors: the operands. */
      private final List<FieldEventDetector<T>> detectors;
  
      /** The composition function. Should be associative for predictable behavior. */
      private final Operator operator;
  
      /**
       * Private constructor with all the parameters.
       *
       * @param detectors    the operands.
       * @param operator     reduction operator to apply to value of the g function of the
       *                     operands.
       * @param detectionSettings event detection settings.
       * @param newHandler   event handler.
       * @since 13.0
       */
      protected FieldBooleanDetector(final List<FieldEventDetector<T>> detectors,
                                     final Operator operator,
                                     final FieldEventDetectionSettings<T> detectionSettings,
                                     final FieldEventHandler<T> newHandler) {
          super(detectionSettings, newHandler);
          this.detectors = detectors;
          this.operator = operator;
      }
  
      /**
       * Create a new event detector that is the logical AND of the given event detectors.
       *
       * <p> The created event detector's g function is positive if and only if the g
       * functions of all detectors in {@code detectors} are positive.
       *
       * <p> The starting interval, threshold, and iteration count are set to the most
      * stringent (minimum) of all the {@code detectors}. The event handlers of the
      * underlying {@code detectors} are not used, instead the default handler is {@link
      * FieldContinueOnEvent}.
      *
      * @param <T> type of the field elements
      * @param detectors the operands. Must contain at least one detector.
      * @return a new event detector that is the logical AND of the operands.
      * @throws NoSuchElementException if {@code detectors} is empty.
      * @see FieldBooleanDetector
      * @see #andCombine(Collection)
      * @see #orCombine(FieldEventDetector...)
      * @see #notCombine(FieldEventDetector)
      */
     @SafeVarargs
     public static <T extends CalculusFieldElement<T>> FieldBooleanDetector<T> andCombine(final FieldEventDetector<T>... detectors) {
         return andCombine(Arrays.asList(detectors));
     }
 
     /**
      * Create a new event detector that is the logical AND of the given event detectors.
      *
      * <p> The created event detector's g function is positive if and only if the g
      * functions of all detectors in {@code detectors} are positive.
      *
      * <p> The starting interval, threshold, and iteration count are set to the most
      * stringent (minimum) of the {@code detectors}. The event handlers of the
      * underlying {@code detectors} are not used, instead the default handler is {@link
      * FieldContinueOnEvent}.
      *
      * @param <T> type of the field elements
      * @param detectors the operands. Must contain at least one detector.
      * @return a new event detector that is the logical AND of the operands.
      * @throws NoSuchElementException if {@code detectors} is empty.
      * @see FieldBooleanDetector
      * @see #andCombine(FieldEventDetector...)
      * @see #orCombine(Collection)
      * @see #notCombine(FieldEventDetector)
      */
     @SuppressWarnings("unchecked")
     public static <T extends CalculusFieldElement<T>> FieldBooleanDetector<T> andCombine(final Collection<? extends FieldEventDetector<T>> detectors) {
         return new FieldBooleanDetector<>(new ArrayList<>(detectors), // copy for immutability
                                           Operator.AND,
                                           new FieldEventDetectionSettings<>(FieldAdaptableInterval.of(Double.POSITIVE_INFINITY, detectors.stream()
                                                   .map(FieldEventDetector::getMaxCheckInterval).toArray(FieldAdaptableInterval[]::new)),
                                           detectors.stream().map(FieldEventDetector::getThreshold).min(new FieldComparator<>()).get(),
                                           detectors.stream().map(FieldEventDetector::getMaxIterationCount).min(Integer::compareTo).get()),
                                           new FieldContinueOnEvent<>());
     }
 
     /**
      * Create a new event detector that is the logical OR of the given event detectors.
      *
      * <p> The created event detector's g function is positive if and only if at least
      * one of g functions of the event detectors in {@code detectors} is positive.
      *
      * <p> The starting interval, threshold, and iteration count are set to the most
      * stringent (minimum) of the {@code detectors}. The event handlers of the
      * underlying EventDetectors are not used, instead the default handler is {@link
      * FieldContinueOnEvent}.
      *
      * @param <T> type of the field elements
      * @param detectors the operands. Must contain at least one detector.
      * @return a new event detector that is the logical OR of the operands.
      * @throws NoSuchElementException if {@code detectors} is empty.
      * @see FieldBooleanDetector
      * @see #orCombine(Collection)
      * @see #andCombine(FieldEventDetector...)
      * @see #notCombine(FieldEventDetector)
      */
     @SafeVarargs
     public static <T extends CalculusFieldElement<T>> FieldBooleanDetector<T> orCombine(final FieldEventDetector<T>... detectors) {
         return orCombine(Arrays.asList(detectors));
     }
 
     /**
      * Create a new event detector that is the logical OR of the given event detectors.
      *
      * <p> The created event detector's g function is positive if and only if at least
      * one of g functions of the event detectors in {@code detectors} is positive.
      *
      * <p> The starting interval, threshold, and iteration count are set to the most
      * stringent (minimum) of the {@code detectors}. The event handlers of the
      * underlying EventDetectors are not used, instead the default handler is {@link
      * FieldContinueOnEvent}.
      *
      * @param <T> type of the field elements
      * @param detectors the operands. Must contain at least one detector.
      * @return a new event detector that is the logical OR of the operands.
      * @throws NoSuchElementException if {@code detectors} is empty.
      * @see FieldBooleanDetector
      * @see #orCombine(FieldEventDetector...)
      * @see #andCombine(Collection)
      * @see #notCombine(FieldEventDetector)
      */
     @SuppressWarnings("unchecked")
     public static <T extends CalculusFieldElement<T>> FieldBooleanDetector<T> orCombine(final Collection<? extends FieldEventDetector<T>> detectors) {
         return new FieldBooleanDetector<>(new ArrayList<>(detectors), // copy for immutability
                                           Operator.OR,
                                           new FieldEventDetectionSettings<>(FieldAdaptableInterval.of(Double.POSITIVE_INFINITY, detectors.stream()
                                                   .map(FieldEventDetector::getMaxCheckInterval).toArray(FieldAdaptableInterval[]::new)),
                                           detectors.stream().map(FieldEventDetector::getThreshold).min(new FieldComparator<>()).get(),
                                           detectors.stream().map(FieldEventDetector::getMaxIterationCount).min(Integer::compareTo).get()),
                                           new FieldContinueOnEvent<>());
     }
 
     /**
      * Create a new event detector that negates the g function of another detector.
      *
      * <p> This detector will be initialized with the same {@link
      * FieldEventDetector#getMaxCheckInterval()}, {@link FieldEventDetector#getThreshold()}, and
      * {@link FieldEventDetector#getMaxIterationCount()} as {@code detector}. The event handler
      * of the underlying detector is not used, instead the default handler is {@link
      * FieldContinueOnEvent}.
      *
      * @param <T> type of the field elements
      * @param detector to negate.
      * @return an new event detector whose g function is the same magnitude but opposite
      * sign of {@code detector}.
      * @see #andCombine(Collection)
      * @see #orCombine(Collection)
      * @see FieldBooleanDetector
      */
     public static <T extends CalculusFieldElement<T>> FieldNegateDetector<T> notCombine(final FieldEventDetector<T> detector) {
         return new FieldNegateDetector<>(detector);
     }
 
     /** {@inheritDoc} */
     @Override
     public boolean dependsOnTimeOnly() {
         return getDetectors().stream().allMatch(FieldEventDetector::dependsOnTimeOnly);
     }
 
     @Override
     public T g(final FieldSpacecraftState<T> s) {
         // can't use stream/lambda here because g(s) throws a checked exception
         // so write out and combine the map and reduce loops
         T ret = s.getDate().getField().getZero().newInstance(Double.NaN); // return value
         boolean first = true;
         for (final FieldEventDetector<T> detector : detectors) {
             if (first) {
                 ret = detector.g(s);
                 first = false;
             } else {
                 ret = operator.combine(ret, detector.g(s));
             }
         }
         // return the result of applying the operator to all operands
         return ret;
     }
 
     @Override
     protected FieldBooleanDetector<T> create(final FieldEventDetectionSettings<T> detectionSettings,
                                              final FieldEventHandler<T> newHandler) {
         return new FieldBooleanDetector<>(detectors, operator, detectionSettings, newHandler);
     }
 
     @Override
     public void init(final FieldSpacecraftState<T> s0,
                      final FieldAbsoluteDate<T> t) {
         super.init(s0, t);
         for (final FieldEventDetector<T> detector : detectors) {
             detector.init(s0, t);
         }
     }
 
     @Override
     public void reset(final FieldSpacecraftState<T> state, final FieldAbsoluteDate<T> target) {
         super.reset(state, target);
         for (final FieldEventDetector<T> detector : detectors) {
             detector.reset(state, target);
         }
     }
 
     @Override
     public void finish(final FieldSpacecraftState<T> state) {
         super.finish(state);
         for (final FieldEventDetector<T> detector : detectors) {
             detector.finish(state);
         }
     }
 
     /**
      * Get the list of original detectors.
      * @return the list of original detectors
      */
     public List<FieldEventDetector<T>> getDetectors() {
         return new ArrayList<>(detectors);
     }
 
     /** Local class for operator. */
     private enum Operator {
 
         /** And operator. */
         AND() {
 
             @Override
             /** {@inheritDoc} */
             public <T extends CalculusFieldElement<T>> T combine(final T g1, final T g2) {
                 return FastMath.min(g1, g2);
             }
 
         },
 
         /** Or operator. */
         OR() {
 
             @Override
             /** {@inheritDoc} */
             public <T extends CalculusFieldElement<T>> T combine(final T g1, final T g2) {
                 return FastMath.max(g1, g2);
             }
 
         };
 
         /** Combine two g functions evaluations.
          * @param <T> type of the field elements
          * @param g1 first evaluation
          * @param g2 second evaluation
          * @return combined evaluation
          */
         public abstract <T extends CalculusFieldElement<T>> T combine(T g1, T g2);
 
     }
 
     /** Comparator for field elements.
      * @param <T> type of the field elements
      */
     private static class FieldComparator<T extends CalculusFieldElement<T>> implements Comparator<T>, Serializable {
         public int compare(final T t1, final T t2) {
             return Double.compare(t1.getReal(), t2.getReal());
         }
     }
 
 }