forked from apache/cloudstack
-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathStateMachine.java
More file actions
147 lines (127 loc) · 4.7 KB
/
Copy pathStateMachine.java
File metadata and controls
147 lines (127 loc) · 4.7 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
//
// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF 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 com.cloud.utils.fsm;
import java.util.ArrayList;
import java.util.Formatter;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
/**
* Specifically, it implements the Moore machine.
* so someone else can add/modify states easily without regression.
* business logic anyways.
*
* @param <S> state
* @param <E> event
*/
public class StateMachine<S, E> {
private final HashMap<S, StateEntry> _states = new HashMap<S, StateEntry>();
private final StateEntry _initialStateEntry;
public StateMachine() {
_initialStateEntry = new StateEntry(null);
}
public void addTransition(S currentState, E event, S toState) {
StateEntry entry = null;
if (currentState == null) {
entry = _initialStateEntry;
} else {
entry = _states.get(currentState);
if (entry == null) {
entry = new StateEntry(currentState);
_states.put(currentState, entry);
}
}
entry.addTransition(event, toState);
entry = _states.get(toState);
if (entry == null) {
entry = new StateEntry(toState);
_states.put(toState, entry);
}
entry.addFromTransition(event, currentState);
}
public Set<E> getPossibleEvents(S s) {
StateEntry entry = _states.get(s);
return entry.nextStates.keySet();
}
public S getNextState(S s, E e) {
StateEntry entry = null;
if (s == null) {
entry = _initialStateEntry;
} else {
entry = _states.get(s);
assert entry != null : "Cannot retrieve transitions for state " + s.toString();
}
return entry.nextStates.get(e);
}
public List<S> getFromStates(S s, E e) {
StateEntry entry = _states.get(s);
if (entry == null) {
return new ArrayList<S>();
}
return entry.prevStates.get(e);
}
@Override
public String toString() {
StringBuilder str = new StringBuilder(1024);
_initialStateEntry.buildString(str);
for (StateEntry entry : _states.values()) {
entry.buildString(str);
}
return str.toString();
}
private class StateEntry {
public S state;
public HashMap<E, S> nextStates;
public HashMap<E, List<S>> prevStates;
public StateEntry(S state) {
this.state = state;
nextStates = new HashMap<E, S>();
prevStates = new HashMap<E, List<S>>();
}
public void addTransition(E e, S s) {
assert !nextStates.containsKey(e) : "State " + getStateStr() + " already contains a transition to state " + nextStates.get(e).toString() + " via event " +
e.toString() + ". Please revisit the rule you're adding to state " + s.toString();
nextStates.put(e, s);
}
public void addFromTransition(E e, S s) {
List<S> l = prevStates.get(e);
if (l == null) {
l = new ArrayList<S>();
prevStates.put(e, l);
}
assert !l.contains(s) : "Already contains the from transition " + e.toString() + " from state " + s.toString() + " to " + getStateStr();
l.add(s);
}
protected String getStateStr() {
return state == null ? "Initial" : state.toString();
}
public void buildString(StringBuilder str) {
str.append("State: ").append(getStateStr()).append("\n");
for (Map.Entry<E, S> nextState : nextStates.entrySet()) {
str.append(" --> Event: ");
Formatter format = new Formatter();
str.append(format.format("%-30s", nextState.getKey().toString()));
str.append("----> State: ");
str.append(nextState.getValue().toString());
str.append("\n");
}
}
}
}