RecordAndContinue.java

/* Contributed in the public domain.
 * 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.handlers;

import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.EventDetector;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

/**
 * Handler that will record every time an event occurs and always return {@link
 * EventHandler.Action#CONTINUE}.
 *
 * <p> As this handler stores all observed events it may consume large amounts
 * of memory depending on the duration of propagation and the frequency of
 * events.
 *
 * @param <T> the type of {@link EventDetector} that this event handler will
 *            handle events for.
 * @author Evan Ward
 */
public class RecordAndContinue<T extends EventDetector>
        implements EventHandler<T> {

    /** A single event detected during propagation. */
    public static class Event<T> {

        /** The observed state. */
        private final SpacecraftState state;
        /** The detector. */
        private final T detector;
        /** The sign of the derivative of the g function. */
        private final boolean increasing;

        /**
         * Create a new event.
         *
         * @param detector   of the event.
         * @param state      of the event.
         * @param increasing if the g function is increasing.
         */
        private Event(final T detector,
                      final SpacecraftState state,
                      final boolean increasing) {
            this.detector = detector;
            this.state = state;
            this.increasing = increasing;
        }

        /**
         * Get the detector.
         *
         * @return the detector that found the event.
         * @see EventHandler#eventOccurred(SpacecraftState, EventDetector,
         * boolean)
         */
        public T getDetector() {
            return detector;
        }

        /**
         * Is the g() function increasing?
         *
         * @return if the sign of the derivative of the g function is positive
         * (true) or negative (false).
         * @see EventHandler#eventOccurred(SpacecraftState, EventDetector,
         * boolean)
         */
        public boolean isIncreasing() {
            return increasing;
        }

        /**
         * Get the spacecraft's state at the event.
         *
         * @return the satellite's state when the event was triggered.
         * @see EventHandler#eventOccurred(SpacecraftState, EventDetector,
         * boolean)
         */
        public SpacecraftState getState() {
            return state;
        }

    }

    /** Observed events. */
    private final List<Event<T>> events;

    /** Create a new handler using an {@link ArrayList} to store events. */
    public RecordAndContinue() {
        this(new ArrayList<>());
    }

    /**
     * Create a handler using the given collection to store events.
     *
     * @param events collection.
     */
    public RecordAndContinue(final List<Event<T>> events) {
        this.events = events;
    }

    /**
     * Get the events passed to this handler.
     *
     * <p> Note the returned list of events is in the order the events were
     * passed to this handler by calling {@link #eventOccurred(SpacecraftState,
     * EventDetector, boolean)}. This may or may not be chronological order.
     *
     * <p> Also not that this method returns a view of the internal collection
     * used to store events and calling any of this handler's methods may modify
     * both the underlying collection and the returned view. If a snapshot of
     * the events up to a certain point is needed create a copy of the returned
     * collection.
     *
     * @return the events observed by the handler in the order they were
     * observed.
     */
    public List<Event<T>> getEvents() {
        return Collections.unmodifiableList(this.events);
    }

    /** Clear all stored events. */
    public void clear() {
        this.events.clear();
    }

    @Override
    public Action eventOccurred(final SpacecraftState s,
                                final T detector,
                                final boolean increasing) {
        events.add(new Event<T>(detector, s, increasing));
        return Action.CONTINUE;
    }

    @Override
    public SpacecraftState resetState(final T detector,
                                      final SpacecraftState oldState) {
        return null;
    }

}