001    /*
002     *  Licensed to the Apache Software Foundation (ASF) under one
003     *  or more contributor license agreements.  See the NOTICE file
004     *  distributed with this work for additional information
005     *  regarding copyright ownership.  The ASF licenses this file
006     *  to you under the Apache License, Version 2.0 (the
007     *  "License"); you may not use this file except in compliance
008     *  with the License.  You may obtain a copy of the License at
009     *  
010     *    http://www.apache.org/licenses/LICENSE-2.0
011     *  
012     *  Unless required by applicable law or agreed to in writing,
013     *  software distributed under the License is distributed on an
014     *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015     *  KIND, either express or implied.  See the License for the
016     *  specific language governing permissions and limitations
017     *  under the License. 
018     *  
019     */
020    package org.apache.directory.shared.asn1.codec.stateful;
021    
022    
023    import java.util.LinkedList;
024    
025    
026    /**
027     * A convenience callback which collects decoded or encoded objects to audit a
028     * codecs's activity. The callback also comes in handy when data is to be pushed
029     * through a codec and grabed immediately afterwords to serialize codec
030     * operation.
031     * 
032     * @author <a href="mailto:dev@directory.apache.org"> Apache Directory Project</a>
033     * @version $Rev: 572195 $
034     */
035    public class CallbackHistory implements DecoderCallback, EncoderCallback
036    {
037        /** history of decoded objects in cronological order */
038        private final LinkedList<Object> history;
039    
040        /** the length of callback history stored */
041        private final int length;
042    
043    
044        /**
045         * Creates an auditing callback that manages a history of indefinite length.
046         */
047        public CallbackHistory()
048        {
049            this( -1 );
050        }
051    
052    
053        /**
054         * Creates an auditing callback that manages a history of fixed or
055         * indefinite length. If the length is fixed the history effectively becomes
056         * a FIFO structure.
057         * 
058         * @param length
059         *            the maximum length of callback history to store before
060         *            dropping decoded items, a length of zero or 1 corresponds to
061         *            indefinite history
062         */
063        public CallbackHistory(int length)
064        {
065            this.length = length;
066            history = new LinkedList<Object>();
067        }
068    
069    
070        /*
071         * (non-Javadoc)
072         * 
073         * @see org.apache.asn1.codec.stateful.DecoderCallback#decodeOccurred(
074         *      org.apache.asn1.codec.stateful.StatefulDecoder, java.lang.Object)
075         */
076        public void decodeOccurred( StatefulDecoder decoder, Object decoded )
077        {
078            if ( length > 0 )
079            {
080                while ( history.size() >= length )
081                {
082                    history.removeLast();
083                }
084            }
085    
086            history.addFirst( decoded );
087        }
088    
089    
090        /**
091         * Callback to deliver a fully encoded object.
092         * 
093         * @param encoder
094         *            the stateful encoder driving the callback
095         * @param encoded
096         *            the object that was encoded
097         */
098        public void encodeOccurred( StatefulEncoder encoder, Object encoded )
099        {
100            if ( length > 0 )
101            {
102                while ( history.size() >= length )
103                {
104                    history.removeLast();
105                }
106            }
107    
108            history.addFirst( encoded );
109        }
110    
111    
112        /**
113         * Gets the most recent decoded object if one exists.
114         * 
115         * @return the most recent decoded object
116         * @throws java.util.NoSuchElementException
117         *             if the history is empty
118         */
119        public Object getMostRecent()
120        {
121            return history.getFirst();
122        }
123    
124    
125        /**
126         * Gets the oldest decoded object if one exists.
127         * 
128         * @return the oldest decoded object
129         * @throws java.util.NoSuchElementException
130         *             if the history is empty
131         */
132        public Object getOldest()
133        {
134            return history.getLast();
135        }
136    
137    
138        /**
139         * Tests to see if the history is empty.
140         * 
141         * @return true if the history is empty, false otherwise
142         */
143        public boolean isEmpty()
144        {
145            return history.isEmpty();
146        }
147    
148    
149        /**
150         * Clears the history of decoded items.
151         */
152        public void clear()
153        {
154            history.clear();
155        }
156    
157    
158        /**
159         * Gets the number of decoded items in the callback history.
160         * 
161         * @return the number of decoded items in the callback history
162         */
163        public int size()
164        {
165            return history.size();
166        }
167    }