1   /* Copyright 2022-2026 Romain Serra
2    * Licensed to CS GROUP (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.functions;
18  
19  import org.hipparchus.CalculusFieldElement;
20  import org.orekit.propagation.FieldSpacecraftState;
21  import org.orekit.propagation.SpacecraftState;
22  import org.orekit.utils.ExtendedStateScalarFunction;
23  
24  /** Time-shifted event function. The value can depend on the state or be constant.
25   * @author Romain Serra
26   * @since 14.0
27   */
28  public class ShiftedEventFunction implements EventFunctionModifier {
29  
30      /** Original event function. */
31      private final EventFunction baseFunction;
32  
33      /** Event time shift. */
34      private final ExtendedStateScalarFunction timeShiftFunction;
35  
36      /**
37       * Constructor with constant shift.
38       * @param baseFunction event function to shift in time
39       * @param timeShift shift value
40       */
41      public ShiftedEventFunction(final EventFunction baseFunction, final double timeShift) {
42          this(baseFunction, ExtendedStateScalarFunction.of(state -> timeShift));
43      }
44  
45      /**
46       * Constructor.
47       * @param baseFunction event function to shift in time
48       * @param timeShiftFunction shift value function
49       */
50      public ShiftedEventFunction(final EventFunction baseFunction, final ExtendedStateScalarFunction timeShiftFunction) {
51          this.baseFunction = baseFunction;
52          this.timeShiftFunction = timeShiftFunction;
53      }
54  
55      /**
56       * Getter for time shift function.
57       * @return shift function
58       */
59      public ExtendedStateScalarFunction getTimeShiftFunction() {
60          return timeShiftFunction;
61      }
62  
63      @Override
64      public EventFunction getBaseFunction() {
65          return baseFunction;
66      }
67  
68      @Override
69      public double value(final SpacecraftState state) {
70          return baseFunction.value(state.shiftedBy(timeShiftFunction.value(state)));
71      }
72  
73      @Override
74      public <T extends CalculusFieldElement<T>> T value(final FieldSpacecraftState<T> fieldState) {
75          return baseFunction.value(fieldState.shiftedBy(timeShiftFunction.value(fieldState)));
76      }
77  
78  }