EventHandler.java

/* Copyright 2013 Applied Defense Solutions, Inc.
 * Licensed to CS Communication & Systèmes (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.hipparchus.ode.events.Action;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.EventDetector;
import org.orekit.time.AbsoluteDate;


/** An interface defining how to handle events occurring during propagation.
 *
 * @author Hank Grabowski
 *
 * @since 6.1
 */
public interface EventHandler {

    /** Initialize event handler at the start of a propagation.
     * <p>
     * This method is called once at the start of the propagation. It
     * may be used by the event handler to initialize some internal data
     * if needed.
     * </p>
     * <p>
     * The default implementation does nothing
     * </p>
     * @param initialState initial state
     * @param target target date for the propagation
     * @param detector event detector related to the event handler
     *
     */
    default void init(SpacecraftState initialState, AbsoluteDate target, final EventDetector detector) {
        // nothing by default
    }

    /** Handle an event.
     *
     * @param s SpaceCraft state to be used in the evaluation
     * @param detector object with appropriate type that can be used in determining correct return state
     * @param increasing with the event occurred in an "increasing" or "decreasing" slope direction
     * @return the Action that the calling detector should pass back to the evaluation system
     *
     */
    Action eventOccurred(SpacecraftState s, EventDetector detector, boolean increasing);

    /** Reset the state prior to continue propagation.
     * <p>This method is called after the step handler has returned and
     * before the next step is started, but only when {@link
     * #eventOccurred} has itself returned the {@link Action#RESET_STATE}
     * indicator. It allows the user to reset the state for the next step,
     * without perturbing the step handler of the finishing step. If the
     * {@link #eventOccurred} never returns the {@link Action#RESET_STATE}
     * indicator, this function will never be called, and it is safe to simply return null.</p>
     * <p>
     * The default implementation simply return its argument.
     * </p>
     * @param detector object with appropriate type that can be used in determining correct return state
     * @param oldState old state
     * @return new state
     */
    default SpacecraftState resetState(EventDetector detector, SpacecraftState oldState) {
        return oldState;
    }


    /**
     * This method finalizes the event handler's job.
     * <p>
     * The default implementation does nothing
     * </p>
     * @param finalState state at propagation end
     * @param detector event detector related to the event handler
     * @since 12.2
     */
    default void finish(final SpacecraftState finalState, final EventDetector detector) {
        // nothing by default
    }

}