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.orekit.errors.OrekitException;
20  import org.orekit.propagation.SpacecraftState;
21  import org.orekit.propagation.events.EventDetector;
22  
23  
24  /**
25   * An interface defining how to override event handling behavior in the standard
26   * propagator eventing classes without requiring subclassing.  In cases where
27   * one wishes to use anonymous classes rather than explicit subclassing this
28   * allows for a more direct way to override the behavior.  Event classes have to
29   * specifically support this capability.
30   *
31   * @author Hank Grabowski
32   *
33   * @param <T> object type that the handler is called from
34   * @since 6.1
35   */
36  public interface EventHandler<T extends EventDetector> {
37  
38      /** Enumerate for actions to be performed when an event occurs. */
39      public enum Action {
40  
41          /** Stop indicator.
42           * <p>This value should be used as the return value of the {@link
43           * #eventOccurred eventOccurred} method when the propagation should be
44           * stopped after the event ending the current step.</p>
45           */
46          STOP,
47  
48          /** Reset state indicator.
49           * <p>This value should be used as the return value of the {@link
50           * #eventOccurred eventOccurred} method when the propagation should
51           * go on after the event ending the current step, with a new state
52           * (which will be retrieved thanks to the {@link #resetState
53           * resetState} method).</p>
54           */
55          RESET_STATE,
56  
57          /** Reset derivatives indicator.
58           * <p>This value should be used as the return value of the {@link
59           * #eventOccurred eventOccurred} method when the propagation should
60           * go on after the event ending the current step, with recomputed
61           * derivatives vector.</p>
62           */
63          RESET_DERIVATIVES,
64  
65          /** Continue indicator.
66           * <p>This value should be used as the return value of the {@link
67           * #eventOccurred eventOccurred} method when the propagation should go
68           * on after the event ending the current step.</p>
69           */
70          CONTINUE;
71  
72      }
73  
74      /**
75       * eventOccurred method mirrors the same interface method as in {@link EventDetector}
76       * and its subclasses, but with an additional parameter that allows the calling
77       * method to pass in an object from the detector which would have potential
78       * additional data to allow the implementing class to determine the correct
79       * return state.
80       *
81       * @param s SpaceCraft state to be used in the evaluation
82       * @param detector object with appropriate type that can be used in determining correct return state
83       * @param increasing with the event occured in an "increasing" or "decreasing" slope direction
84       * @return the Action that the calling detector should pass back to the evaluation system
85       *
86       * @exception OrekitException if some specific error occurs
87       */
88      Action eventOccurred(SpacecraftState s, T detector, boolean increasing) throws OrekitException;
89  
90      /** Reset the state prior to continue propagation.
91       * <p>This method is called after the step handler has returned and
92       * before the next step is started, but only when {@link
93       * #eventOccurred} has itself returned the {@link Action#RESET_STATE}
94       * indicator. It allows the user to reset the state for the next step,
95       * without perturbing the step handler of the finishing step. If the
96       * {@link #eventOccurred} never returns the {@link Action#RESET_STATE}
97       * indicator, this function will never be called, and it is safe to simply return null.</p>
98       * @param detector object with appropriate type that can be used in determining correct return state
99       * @param oldState old state
100      * @return new state
101      * @exception OrekitException if the state cannot be reseted
102      */
103     SpacecraftState resetState(T detector, SpacecraftState oldState) throws OrekitException;
104 
105 }