/*
* 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.commons.net.nntp;
/**
* This is an implementation of a message threading algorithm, as originally devised by Zamie Zawinski.
* See <a href="http://www.jwz.org/doc/threading.html">http://www.jwz.org/doc/threading.html</a> for details.
* For his Java implementation, see <a href="http://lxr.mozilla.org/mozilla/source/grendel/sources/grendel/view/Threader.java">http://lxr.mozilla.org/mozilla/source/grendel/sources/grendel/view/Threader.java</a>
*
* @author rwinston <rwinston@checkfree.com>
*
*/
import java.util.HashMap;
import java.util.Iterator;
public class Threader {
private ThreadContainer root;
private HashMap<String,ThreadContainer> idTable;
private int bogusIdCount = 0;
/**
* The main threader entry point - The client passes in an array of Threadable objects, and
* the Threader constructs a connected 'graph' of messages
* @param messages
* @return
*/
public Threadable thread(Threadable[] messages) {
if (messages == null)
return null;
idTable = new HashMap<String,ThreadContainer>();
// walk through each Threadable element
for (int i = 0; i < messages.length; ++i) {
if (!messages[i].isDummy())
buildContainer(messages[i]);
}
root = findRootSet();
idTable.clear();
idTable = null;
pruneEmptyContainers(root);
root.reverseChildren();
gatherSubjects();
if (root.next != null)
throw new RuntimeException("root node has a next:" + root);
for (ThreadContainer r = root.child; r != null; r = r.next) {
if (r.threadable == null)
r.threadable = r.child.threadable.makeDummy();
}
Threadable result = (root.child == null ? null : root.child.threadable);
root.flush();
root = null;
return result;
}
/**
*
* @param threadable
*/
private void buildContainer(Threadable threadable) {
String id = threadable.messageThreadId();
ThreadContainer container = idTable.get(id);
// A ThreadContainer exists for this id already. This should be a forward reference, but may
// be a duplicate id, in which case we will need to generate a bogus placeholder id
if (container != null) {
if (container.threadable != null) { // oops! duplicate ids...
id = "<Bogus-id:" + (bogusIdCount++) + ">";
container = null;
} else {
// The container just contained a forward reference to this message, so let's
// fill in the threadable field of the container with this message
container.threadable = threadable;
}
}
// No container exists for that message Id. Create one and insert it into the hash table.
if (container == null) {
container = new ThreadContainer();
container.threadable = threadable;
idTable.put(id, container);
}
// Iterate through all of the references and create ThreadContainers for any references that
// don't have them.
ThreadContainer parentRef = null;
{
String[] references = threadable.messageThreadReferences();
for (int i = 0; i < references.length; ++i) {
String refString = references[i];
ThreadContainer ref = idTable.get(refString);
// if this id doesnt have a container, create one
if (ref == null) {
ref = new ThreadContainer();
idTable.put(refString, ref);
}
// Link references together in the order they appear in the References: header,
// IF they dont have a have a parent already &&
// IF it will not cause a circular reference
if ((parentRef != null)
&& (ref.parent == null)
&& (parentRef != ref)
&& !(parentRef.findChild(ref))) {
// Link ref into the parent's child list
ref.parent = parentRef;
ref.next = parentRef.child;
parentRef.child = ref;
}
parentRef = ref;
}
}
// parentRef is now set to the container of the last element in the references field. make that
// be the parent of this container, unless doing so causes a circular reference
if (parentRef != null
&& (parentRef == container || container.findChild(parentRef)))
parentRef = null;
// if it has a parent already, its because we saw this message in a References: field, and presumed
// a parent based on the other entries in that field. Now that we have the actual message, we can
// throw away the old parent and use this new one
if (container.parent != null) {
ThreadContainer rest, prev;
for (prev = null, rest = container.parent.child;
rest != null;
prev = rest, rest = rest.next) {
if (rest == container)
break;
}
if (rest == null) {
throw new RuntimeException(
"Didnt find "
+ container
+ " in parent"
+ container.parent);
}
// Unlink this container from the parent's child list
if (prev == null)
container.parent.child = container.next;
else
prev.next = container.next;
container.next = null;
container.parent = null;
}
// If we have a parent, link container into the parents child list
if (parentRef != null) {
container.parent = parentRef;
container.next = parentRef.child;
parentRef.child = container;
}
}
/**
* Find the root set of all existing ThreadContainers
* @return root the ThreadContainer representing the root node
*/
private ThreadContainer findRootSet() {
ThreadContainer root = new ThreadContainer();
Iterator<String> iter = idTable.keySet().iterator();
while (iter.hasNext()) {
Object key = iter.next();
ThreadContainer c = idTable.get(key);
if (c.parent == null) {
if (c.next != null)
throw new RuntimeException(
"c.next is " + c.next.toString());
c.next = root.child;
root.child = c;
}
}
return root;
}
/**
* Delete any empty or dummy ThreadContainers
* @param parent
*/
private void pruneEmptyContainers(ThreadContainer parent) {
ThreadContainer container, prev, next;
for (prev = null, container = parent.child, next = container.next;
container != null;
prev = container,
container = next,
next = (container == null ? null : container.next)) {
// Is it empty and without any children? If so,delete it
if (container.threadable == null && container.child == null) {
if (prev == null)
parent.child = container.next;
else
prev.next = container.next;
// Set container to prev so that prev keeps its same value the next time through the loop
container = prev;
}
// Else if empty, with kids, and (not at root or only one kid)
else if (
container.threadable == null
&& container.child != null
&& (container.parent != null
|| container.child.next == null)) {
// We have an invalid/expired message with kids. Promote the kids to this level.
ThreadContainer tail;
ThreadContainer kids = container.child;
// Remove this container and replace with 'kids'.
if (prev == null)
parent.child = kids;
else
prev.next = kids;
// Make each child's parent be this level's parent -> i.e. promote the children. Make the last child's next point to this container's next
// i.e. splice kids into the list in place of container
for (tail = kids; tail.next != null; tail = tail.next)
tail.parent = container.parent;
tail.parent = container.parent;
tail.next = container.next;
// next currently points to the item after the inserted items in the chain - reset that so we process the newly
// promoted items next time round
next = kids;
// Set container to prev so that prev keeps its same value the next time through the loop
container = prev;
} else if (container.child != null) {
// A real message , with kids
// Iterate over the children
pruneEmptyContainers(container);
}
}
}
/**
* If any two members of the root set have the same subject, merge them. This is to attempt to accomodate messages without References: headers.
*/
private void gatherSubjects() {
int count = 0;
for (ThreadContainer c = root.child; c != null; c = c.next)
count++;
// TODO verify this will avoid rehashing
HashMap<String, ThreadContainer> subjectTable = new HashMap<String, ThreadContainer>((int) (count * 1.2), (float) 0.9);
count = 0;
for (ThreadContainer c = root.child; c != null; c = c.next) {
Threadable threadable = c.threadable;
// No threadable? If so, it is a dummy node in the root set.
// Only root set members may be dummies, and they alway have at least 2 kids
// Take the first kid as representative of the subject
if (threadable == null)
threadable = c.child.threadable;
String subj = threadable.simplifiedSubject();
if (subj == null || subj == "")
continue;
ThreadContainer old = subjectTable.get(subj);
// Add this container to the table iff:
// - There exists no container with this subject
// - or this is a dummy container and the old one is not - the dummy one is
// more interesting as a root, so put it in the table instead
// - The container in the table has a "Re:" version of this subject, and
// this container has a non-"Re:" version of this subject. The non-"Re:" version
// is the more interesting of the two.
if (old == null
|| (c.threadable == null && old.threadable != null)
|| (old.threadable != null
&& old.threadable.subjectIsReply()
&& c.threadable != null
&& !c.threadable.subjectIsReply())) {
subjectTable.put(subj, c);
count++;
}
}
// If the table is empty, we're done
if (count == 0)
return;
// subjectTable is now populated with one entry for each subject which occurs in the
// root set. Iterate over the root set, and gather together the difference.
ThreadContainer prev, c, rest;
for (prev = null, c = root.child, rest = c.next;
c != null;
prev = c, c = rest, rest = (rest == null ? null : rest.next)) {
Threadable threadable = c.threadable;
// is it a dummy node?
if (threadable == null)
threadable = c.child.threadable;
String subj = threadable.simplifiedSubject();
// Dont thread together all subjectless messages
if (subj == null || subj == "")
continue;
ThreadContainer old = subjectTable.get(subj);
if (old == c) // That's us
continue;
// We have now found another container in the root set with the same subject
// Remove the "second" message from the root set
if (prev == null)
root.child = c.next;
else
prev.next = c.next;
c.next = null;
if (old.threadable == null && c.threadable == null) {
// both dummies - merge them
ThreadContainer tail;
for (tail = old.child;
tail != null && tail.next != null;
tail = tail.next);
tail.next = c.child;
for (tail = c.child; tail != null; tail = tail.next)
tail.parent = old;
c.child = null;
} else if (
old.threadable == null
|| (c.threadable != null
&& c.threadable.subjectIsReply()
&& !old.threadable.subjectIsReply())) {
// Else if old is empty, or c has "Re:" and old does not ==> make this message a child of old
c.parent = old;
c.next = old.child;
old.child = c;
} else {
// else make the old and new messages be children of a new dummy container.
// We create a new container object for old.msg and empty the old container
ThreadContainer newc = new ThreadContainer();
newc.threadable = old.threadable;
newc.child = old.child;
for (ThreadContainer tail = newc.child;
tail != null;
tail = tail.next)
tail.parent = newc;
old.threadable = null;
old.child = null;
c.parent = old;
newc.parent = old;
// Old is now a dummy- give it 2 kids , c and newc
old.child = c;
c.next = newc;
}
// We've done a merge, so keep the same prev
c = prev;
}
subjectTable.clear();
subjectTable = null;
}
}
/**
* A placeholder utility class, used for constructing a tree of Threadables
* Originall implementation by Jamie Zawinski.
* See the Grendel source for more details <a href="http://lxr.mozilla.org/mozilla/source/grendel/sources/grendel/view/Threader.java#511">here</a>
* Threadable objects
* @author Rory Winston <rwinston@checkfree.com>
*/
class ThreadContainer {
Threadable threadable;
ThreadContainer parent;
ThreadContainer prev;
ThreadContainer next;
ThreadContainer child;
/**
*
* @param container
* @return true if child is under self's tree. Detects circular references
*/
boolean findChild(ThreadContainer target) {
if (child == null)
return false;
else if (child == target)
return true;
else
return child.findChild(target);
}
// Copy the ThreadContainer tree structure down into the underlying Threadable objects
// (Make the Threadable tree look like the ThreadContainer tree)
void flush() {
if (parent != null && threadable == null)
throw new RuntimeException("no threadable in " + this.toString());
parent = null;
if (threadable != null)
threadable.setChild(child == null ? null : child.threadable);
if (child != null) {
child.flush();
child = null;
}
if (threadable != null)
threadable.setNext(next == null ? null : next.threadable);
if (next != null) {
next.flush();
next = null;
}
threadable = null;
}
/**
* Reverse the entire set of children
*
*/
void reverseChildren() {
if (child != null) {
ThreadContainer kid, prev, rest;
for (prev = null, kid = child, rest = kid.next;
kid != null;
prev = kid,
kid = rest,
rest = (rest == null ? null : rest.next))
kid.next = prev;
child = prev;
// Do it for the kids
for (kid = child; kid != null; kid = kid.next)
kid.reverseChildren();
}
}
}