/* Copyright 2002-2022 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.propagation.events;
  
  import java.util.List;
  import java.util.stream.Collectors;
  
  import org.hipparchus.CalculusFieldElement;
  import org.hipparchus.Field;
  import org.hipparchus.util.FastMath;
  import org.orekit.errors.OrekitException;
  import org.orekit.errors.OrekitMessages;
  import org.orekit.propagation.FieldSpacecraftState;
  import org.orekit.propagation.events.handlers.FieldEventHandler;
  import org.orekit.propagation.events.handlers.FieldStopOnEvent;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.utils.DateDriver;
  import org.orekit.utils.ParameterDriver;
  import org.orekit.utils.ParameterObserver;
  
  /** Detector for date intervals that may be offset thanks to parameter drivers.
   * <p>
   * Two dual views can be used for date intervals: either start date/stop date or
   * median date/duration. {@link #getStartDriver() start}/{@link #getStopDriver() stop}
   * drivers and {@link #getMedianDriver() median}/{@link #getDurationDriver() duration}
   * drivers work in pair. Both drivers in one pair can be selected and their changes will
   * be propagated to the other pair, but attempting to select drivers in both
   * pairs at the same time will trigger an exception. Changing the value of a driver
   * that is not selected should be avoided as it leads to inconsistencies between the pairs.
   * </p>
   * @see org.orekit.propagation.Propagator#addEventDetector(EventDetector)
   * @param <T> type of the field elements
   * @author Luc Maisonobe
   * @since 11.1
   */
  public class FieldParameterDrivenDateIntervalDetector<T extends CalculusFieldElement<T>> extends FieldAbstractDetector<FieldParameterDrivenDateIntervalDetector<T>, T> {
  
      /** Default suffix for start driver. */
      public static final String START_SUFFIX = "_START";
  
      /** Default suffix for stop driver. */
      public static final String STOP_SUFFIX = "_STOP";
  
      /** Default suffix for median driver. */
      public static final String MEDIAN_SUFFIX = "_MEDIAN";
  
      /** Default suffix for duration driver. */
      public static final String DURATION_SUFFIX = "_DURATION";
  
      /** Reference interval start driver. */
      private DateDriver start;
  
      /** Reference interval stop driver. */
      private DateDriver stop;
  
      /** Median date driver. */
      private DateDriver median;
  
      /** Duration driver. */
      private ParameterDriver duration;
  
      /** Build a new instance.
       * @param field field to which the elements belong
       * @param prefix prefix to use for parameter drivers names
       * @param refMedian reference interval median date
       * @param refDuration reference duration
       */
      public FieldParameterDrivenDateIntervalDetector(final Field<T> field, final String prefix,
                                                      final AbsoluteDate refMedian, final double refDuration) {
          this(field, prefix,
               refMedian.shiftedBy(-0.5 * refDuration),
               refMedian.shiftedBy(+0.5 * refDuration));
      }
  
      /** Build a new instance.
       * @param field field to which the elements belong
       * @param prefix prefix to use for parameter drivers names
       * @param refStart reference interval start date
       * @param refStop reference interval stop date
       */
      public FieldParameterDrivenDateIntervalDetector(final Field<T> field, final String prefix,
                                                      final AbsoluteDate refStart, final AbsoluteDate refStop) {
          this(field.getZero().newInstance(DEFAULT_MAXCHECK),
               field.getZero().newInstance(DEFAULT_THRESHOLD),
               DEFAULT_MAX_ITER,
              new FieldStopOnEvent<FieldParameterDrivenDateIntervalDetector<T>, T>(),
              new DateDriver(refStart, prefix + START_SUFFIX, true),
              new DateDriver(refStop, prefix + STOP_SUFFIX, false),
              new DateDriver(refStart.shiftedBy(0.5 * refStop.durationFrom(refStart)), prefix + MEDIAN_SUFFIX, true),
              new ParameterDriver(prefix + DURATION_SUFFIX, refStop.durationFrom(refStart), 1.0, 0.0, Double.POSITIVE_INFINITY));
     }
 
     /** 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 start reference interval start driver
      * @param stop reference interval stop driver
      * @param median median date driver
      * @param duration duration driver
      */
     private FieldParameterDrivenDateIntervalDetector(final T maxCheck, final T threshold, final int maxIter,
                                                      final FieldEventHandler<? super FieldParameterDrivenDateIntervalDetector<T>, T> handler,
                                                      final DateDriver start, final DateDriver stop,
                                                      final DateDriver median, final ParameterDriver duration) {
         super(maxCheck, threshold, maxIter, handler);
         this.start    = start;
         this.stop     = stop;
         this.median   = median;
         this.duration = duration;
 
         // set up delegation between drivers
         replaceBindingObserver(start,    new StartObserver());
         replaceBindingObserver(stop,     new StopObserver());
         replaceBindingObserver(median,   new MedianObserver());
         replaceBindingObserver(duration, new DurationObserver());
 
     }
 
     /** Replace binding observers.
      * @param driver driver for whose binding observers should be replaced
      * @param bindingObserver new binding observer
      */
     private void replaceBindingObserver(final ParameterDriver driver, final BindingObserver bindingObserver) {
 
         // remove the previous binding observers
         final List<ParameterObserver> original = driver.
                                                  getObservers().
                                                  stream().
                                                  filter(observer -> observer instanceof FieldParameterDrivenDateIntervalDetector.BindingObserver).
                                                  collect(Collectors.toList());
         original.forEach(observer -> driver.removeObserver(observer));
 
         driver.addObserver(bindingObserver);
 
     }
 
     /** {@inheritDoc} */
     @Override
     protected FieldParameterDrivenDateIntervalDetector<T> create(final T newMaxCheck, final T newThreshold, final int newMaxIter,
                                                                  final FieldEventHandler<? super FieldParameterDrivenDateIntervalDetector<T>, T> newHandler) {
         return new FieldParameterDrivenDateIntervalDetector<>(newMaxCheck, newThreshold, newMaxIter, newHandler,
                                                               start, stop, median, duration);
     }
 
     /** Get the driver for start date.
      * <p>
      * Note that the start date is automatically adjusted if either
      * {@link #getMedianDriver() median date} or {@link #getDurationDriver() duration}
      * are {@link ParameterDriver#isSelected() selected} and changed.
      * </p>
      * @return driver for start date
      */
     public DateDriver getStartDriver() {
         return start;
     }
 
     /** Get the driver for stop date.
      * <p>
      * Note that the stop date is automatically adjusted if either
      * {@link #getMedianDriver() median date} or {@link #getDurationDriver() duration}
      * are {@link ParameterDriver#isSelected() selected} changed.
      * </p>
      * @return driver for stop date
      */
     public DateDriver getStopDriver() {
         return stop;
     }
 
     /** Get the driver for median date.
      * <p>
      * Note that the median date is automatically adjusted if either
      * {@link #getStartDriver()} start date or {@link #getStopDriver() stop date}
      * are {@link ParameterDriver#isSelected() selected} changed.
      * </p>
      * @return driver for median date
      */
     public DateDriver getMedianDriver() {
         return median;
     }
 
     /** Get the driver for duration.
      * <p>
      * Note that the duration is automatically adjusted if either
      * {@link #getStartDriver()} start date or {@link #getStopDriver() stop date}
      * are {@link ParameterDriver#isSelected() selected} changed.
      * </p>
      * @return driver for duration
      */
     public ParameterDriver getDurationDriver() {
         return duration;
     }
 
     /** Compute the value of the switching function.
      * <p>
      * The function is positive for dates within the interval defined
      * by applying the parameter drivers shifts to reference dates,
      * and negative for dates outside of this interval. Note that
      * if Δt_start - Δt_stop is less than ref_stop.durationFrom(ref_start),
      * then the interval degenerates to empty and the function never
      * reaches positive values.
      * </p>
      * @param s the current state information: date, kinematics, attitude
      * @return value of the switching function
      */
     public T g(final FieldSpacecraftState<T> s) {
         return FastMath.min(s.getDate().durationFrom(start.getDate()),
                             s.getDate().durationFrom(stop.getDate()).negate());
     }
 
     /** Base observer. */
     private abstract class BindingObserver implements ParameterObserver {
 
         /** {@inheritDoc} */
         @Override
         public void valueChanged(final double previousValue, final ParameterDriver driver) {
             if (driver.isSelected()) {
                 setDelta(driver.getValue() - previousValue);
             }
         }
 
         /** {@inheritDoc} */
         @Override
         public void selectionChanged(final boolean previousSelection, final ParameterDriver driver) {
             if ((start.isSelected()  || stop.isSelected()) &&
                 (median.isSelected() || duration.isSelected())) {
                 throw new OrekitException(OrekitMessages.INCONSISTENT_SELECTION,
                                           start.getName(), stop.getName(),
                                           median.getName(), duration.getName());
             }
         }
 
         /** Change a value.
          * @param delta change of value
          */
         protected abstract void setDelta(double delta);
 
     }
 
     /** Observer for start date. */
     private class StartObserver extends BindingObserver {
         /** {@inheritDoc} */
         @Override
         protected void setDelta(final double delta) {
             median.setValue(median.getValue() + 0.5 * delta);
             duration.setValue(duration.getValue() - delta);
         }
     }
 
     /** Observer for stop date. */
     private class StopObserver extends BindingObserver {
         /** {@inheritDoc} */
         @Override
         protected void setDelta(final double delta) {
             median.setValue(median.getValue() + 0.5 * delta);
             duration.setValue(duration.getValue() + delta);
         }
     }
 
     /** Observer for median date. */
     private class MedianObserver extends BindingObserver {
         /** {@inheritDoc} */
         @Override
         protected void setDelta(final double delta) {
             start.setValue(start.getValue() + delta);
             stop.setValue(stop.getValue() + delta);
         }
     }
 
     /** Observer for duration. */
     private class DurationObserver extends BindingObserver {
         /** {@inheritDoc} */
         @Override
         protected void setDelta(final double delta) {
             start.setValue(start.getValue() - 0.5 * delta);
             stop.setValue(stop.getValue() + 0.5 * delta);
         }
     }
 
 }