/*
* 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 org.apache.sling.mailarchiveserver.impl;
import static java.lang.Character.isLetterOrDigit;
import static org.apache.sling.mailarchiveserver.impl.MessageStoreImpl.makeJcrFriendly;
import static org.apache.sling.mailarchiveserver.impl.MessageStoreImpl.removeRe;
import org.apache.felix.scr.annotations.Component;
import org.apache.felix.scr.annotations.Service;
import org.apache.james.mime4j.dom.Message;
import org.apache.sling.mailarchiveserver.api.ThreadKeyGenerator;
@Component
@Service(ThreadKeyGenerator.class)
public class ThreadKeyGeneratorImpl implements ThreadKeyGenerator {
/**
* These constants are gotten by sampling around 1500 messages
* from some open source projects using SubjectLettersEntropy class.
*
* Entropy of each letter position of the subject was calculated. And two letter positions
* with biggest entropy and occurrence in at least 90% of the messages were chosen.
*
* In order to {@link #getThreadKey(Message)} works correctly, following invariant should hold: LETTER_POS_WITH_BIGGEST_ENTROPY < LETTER_POS_WITH_2ND_BIGGEST_ENTROPY
*/
private static final int LETTER_POS_WITH_BIGGEST_ENTROPY = 9;
private static final int LETTER_POS_WITH_2ND_BIGGEST_ENTROPY = 40;
private static final String UNADDRESSABLE_SUBJECT = "unaddressable subject";
public String getThreadKey(String subject) {
String wordCharsSubj;
String noReSubj;
if (subject != null) {
noReSubj = removeRe(subject);
wordCharsSubj = noReSubj.replaceAll("\\W", "_");
if (!isAddressable(wordCharsSubj)) {
noReSubj = wordCharsSubj = UNADDRESSABLE_SUBJECT;
}
} else {
noReSubj = wordCharsSubj = UNADDRESSABLE_SUBJECT;
}
char prefix1;
char prefix2;
prefix1 = assignPrefix(wordCharsSubj, LETTER_POS_WITH_BIGGEST_ENTROPY);
prefix2 = assignPrefix(wordCharsSubj, LETTER_POS_WITH_2ND_BIGGEST_ENTROPY);
return ""+prefix1+"/"+prefix1+prefix2+"/"+ makeJcrFriendly(noReSubj);
}
private static boolean isAddressable(String subject) {
for (char c : subject.toCharArray()) {
if (isLetterOrDigit(c)) {
return true;
}
}
return false;
}
private static char assignPrefix(String subject, int length) {
char prefix;
if (subject.length() > length) {
int i = length;
while (i > -1 && !isLetterOrDigit(subject.charAt(i)))
i--;
if (i > -1)
prefix = subject.charAt(i);
else {
i = length;
while (i<subject.length() && !isLetterOrDigit(subject.charAt(i)))
i++;
if (i<subject.length())
prefix = subject.charAt(i);
else
throw new IllegalArgumentException();
}
} else {
int i = subject.length()-1;
while (i > -1 && !isLetterOrDigit(subject.charAt(i)))
i--;
if (i > -1)
prefix = subject.charAt(i);
else
throw new IllegalArgumentException();
}
return prefix;
}
}