1   /* Copyright 2013 Applied Defense Solutions, Inc.
2    * Licensed to CS Communication & Systèmes (CS) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * CS licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *   http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.orekit.propagation.events.handlers;
18  
19  import org.hipparchus.ode.events.Action;
20  import org.orekit.propagation.SpacecraftState;
21  import org.orekit.propagation.events.EventDetector;
22  import org.orekit.time.AbsoluteDate;
23  
24  
25  /** An interface defining how to handle events occurring during propagation.
26   *
27   * @author Hank Grabowski
28   *
29   * @since 6.1
30   */
31  public interface EventHandler {
32  
33      /** Initialize event handler at the start of a propagation.
34       * <p>
35       * This method is called once at the start of the propagation. It
36       * may be used by the event handler to initialize some internal data
37       * if needed.
38       * </p>
39       * <p>
40       * The default implementation does nothing
41       * </p>
42       * @param initialState initial state
43       * @param target target date for the propagation
44       * @param detector event detector related to the event handler
45       *
46       */
47      default void init(SpacecraftState initialState, AbsoluteDate target, final EventDetector detector) {
48          // nothing by default
49      }
50  
51      /** Handle an event.
52       *
53       * @param s SpaceCraft state to be used in the evaluation
54       * @param detector object with appropriate type that can be used in determining correct return state
55       * @param increasing with the event occurred in an "increasing" or "decreasing" slope direction
56       * @return the Action that the calling detector should pass back to the evaluation system
57       *
58       */
59      Action eventOccurred(SpacecraftState s, EventDetector detector, boolean increasing);
60  
61      /** Reset the state prior to continue propagation.
62       * <p>This method is called after the step handler has returned and
63       * before the next step is started, but only when {@link
64       * #eventOccurred} has itself returned the {@link Action#RESET_STATE}
65       * indicator. It allows the user to reset the state for the next step,
66       * without perturbing the step handler of the finishing step. If the
67       * {@link #eventOccurred} never returns the {@link Action#RESET_STATE}
68       * indicator, this function will never be called, and it is safe to simply return null.</p>
69       * <p>
70       * The default implementation simply return its argument.
71       * </p>
72       * @param detector object with appropriate type that can be used in determining correct return state
73       * @param oldState old state
74       * @return new state
75       */
76      default SpacecraftState resetState(EventDetector detector, SpacecraftState oldState) {
77          return oldState;
78      }
79  
80  }