DateDetector.java

/* Copyright 2002-2017 CS Systèmes d'Information
 * Licensed to CS Systèmes d'Information (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 org.orekit.errors.OrekitIllegalArgumentException;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitMessages;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.propagation.events.handlers.StopOnEvent;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.TimeStamped;

/** Finder for date events.
 * <p>This class finds date events (i.e. occurrence of some predefined dates).</p>
 * <p>As of version 5.1, it is an enhanced date detector:</p>
 * <ul>
 *   <li>it can be defined without prior date ({@link #DateDetector(double, double, TimeStamped...)})</li>
 *   <li>several dates can be added ({@link #addEventDate(AbsoluteDate)})</li>
 * </ul>
 * <p>The gap between the added dates must be more than the maxCheck.</p>
 * <p>The default implementation behavior is to {@link
 * org.orekit.propagation.events.handlers.EventHandler.Action#STOP stop}
 * propagation at the first event date occurrence. This can be changed by calling
 * {@link #withHandler(EventHandler)} after construction.</p>
 * @see org.orekit.propagation.Propagator#addEventDetector(EventDetector)
 * @author Luc Maisonobe
 * @author Pascal Parraud
 */
public class DateDetector extends AbstractDetector<DateDetector> implements TimeStamped {

    /** Serializable UID. */
    private static final long serialVersionUID = 20131118L;

    /** Last date for g computation. */
    private AbsoluteDate gDate;

    /** List of event dates. */
    private final ArrayList<EventDate> eventDateList;

    /** Current event date. */
    private int currentIndex;

    /** Build a new instance.
     * <p>First event dates are set here, but others can be
     * added later with {@link #addEventDate(AbsoluteDate)}.</p>
     * @param maxCheck maximum checking interval (s)
     * @param threshold convergence threshold (s)
     * @param dates list of event dates
     * @see #addEventDate(AbsoluteDate)
     */
    public DateDetector(final double maxCheck, final double threshold, final TimeStamped... dates) {
        this(maxCheck, threshold, DEFAULT_MAX_ITER, new StopOnEvent<DateDetector>(), dates);
    }

    /** Build a new instance.
     * <p>This constructor is dedicated to single date detection.
     * {@link #getMaxCheckInterval() max check interval} is set to 1.0e10, so almost
     * no other date can be added. Tolerance is set to 1.0e-9.</p>
     * @param target target date
     * @see #addEventDate(AbsoluteDate)
     */
    public DateDetector(final AbsoluteDate target) {
        this(1.0e10, 1.e-9, target);
    }

    /** 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 dates list of event dates
     * @since 6.1
     */
    private DateDetector(final double maxCheck, final double threshold,
                         final int maxIter, final EventHandler<? super DateDetector> handler,
                         final TimeStamped... dates) {
        super(maxCheck, threshold, maxIter, handler);
        this.currentIndex  = -1;
        this.gDate         = null;
        this.eventDateList = new ArrayList<DateDetector.EventDate>(dates.length);
        for (final TimeStamped ts : dates) {
            addEventDate(ts.getDate());
        }
    }

    /** {@inheritDoc} */
    @Override
    protected DateDetector create(final double newMaxCheck, final double newThreshold,
                                  final int newMaxIter, final EventHandler<? super DateDetector> newHandler) {
        return new DateDetector(newMaxCheck, newThreshold, newMaxIter, newHandler,
                                eventDateList.toArray(new EventDate[eventDateList.size()]));
    }

    /** Compute the value of the switching function.
     * This function measures the difference between the current and the target date.
     * @param s the current state information: date, kinematics, attitude
     * @return value of the switching function
     * @exception OrekitException if some specific error occurs
     */
    public double g(final SpacecraftState s) throws OrekitException {
        gDate = s.getDate();
        if (currentIndex < 0) {
            return -1.0;
        } else {
            final EventDate event = getClosest(gDate);
            return event.isgIncrease() ? gDate.durationFrom(event.getDate()) : event.getDate().durationFrom(gDate);
        }
    }

    /** Get the current event date according to the propagator.
     * @return event date
     */
    public AbsoluteDate getDate() {
        return currentIndex < 0 ? null : eventDateList.get(currentIndex).getDate();
    }

    /** Add an event date.
     * <p>The date to add must be:</p>
     * <ul>
     *   <li>less than the smallest already registered event date minus the maxCheck</li>
     *   <li>or more than the largest already registered event date plus the maxCheck</li>
     * </ul>
     * @param target target date
     * @throws IllegalArgumentException if the date is too close from already defined interval
     * @see #DateDetector(double, double, TimeStamped...)
     */
    public void addEventDate(final AbsoluteDate target) throws IllegalArgumentException {
        final boolean increasing;
        if (currentIndex < 0) {
            increasing = (gDate == null) ? true : target.durationFrom(gDate) > 0.0;
            currentIndex = 0;
            eventDateList.add(new EventDate(target, increasing));
        } else {
            final int lastIndex = eventDateList.size() - 1;
            if (eventDateList.get(0).getDate().durationFrom(target) > getMaxCheckInterval()) {
                increasing = !eventDateList.get(0).isgIncrease();
                eventDateList.add(0, new EventDate(target, increasing));
                currentIndex++;
            } else if (target.durationFrom(eventDateList.get(lastIndex).getDate()) > getMaxCheckInterval()) {
                increasing = !eventDateList.get(lastIndex).isgIncrease();
                eventDateList.add(new EventDate(target, increasing));
            } else {
                throw new OrekitIllegalArgumentException(OrekitMessages.EVENT_DATE_TOO_CLOSE,
                                                         target,
                                                         eventDateList.get(0).getDate(),
                                                         eventDateList.get(lastIndex).getDate(),
                                                         getMaxCheckInterval());
            }
        }
    }

    /** Get the closest EventDate to the target date.
     * @param target target date
     * @return current EventDate
     */
    private EventDate getClosest(final AbsoluteDate target) {
        final double dt = target.durationFrom(eventDateList.get(currentIndex).getDate());
        if (dt < 0.0 && currentIndex > 0) {
            boolean found = false;
            while (currentIndex > 0 && !found) {
                if (target.durationFrom(eventDateList.get(currentIndex - 1).getDate()) < eventDateList.get(currentIndex).getDate().durationFrom(target)) {
                    currentIndex--;
                } else {
                    found = true;
                }
            }
        } else if (dt > 0.0 && currentIndex < eventDateList.size() - 1) {
            final int maxIndex = eventDateList.size() - 1;
            boolean found = false;
            while (currentIndex < maxIndex && !found) {
                if (target.durationFrom(eventDateList.get(currentIndex + 1).getDate()) > eventDateList.get(currentIndex).getDate().durationFrom(target)) {
                    currentIndex++;
                } else {
                    found = true;
                }
            }
        }
        return eventDateList.get(currentIndex);
    }

    /** Event date specification. */
    private static class EventDate implements Serializable, TimeStamped {

        /** Serializable UID. */
        private static final long serialVersionUID = -7641032576122527149L;

        /** Event date. */
        private final AbsoluteDate eventDate;

        /** Flag for g function way around event date. */
        private final boolean gIncrease;

        /** Simple constructor.
         * @param date date
         * @param increase if true, g function increases around event date
         */
        EventDate(final AbsoluteDate date, final boolean increase) {
            this.eventDate = date;
            this.gIncrease = increase;
        }

        /** Getter for event date.
         * @return event date
         */
        public AbsoluteDate getDate() {
            return eventDate;
        }

        /** Getter for g function way at event date.
         * @return g function increasing flag
         */
        public boolean isgIncrease() {
            return gIncrease;
        }

    }

}