/*****************************************************************
* 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.
****************************************************************/
/* ====================================================================
*
* Copyright(c) 2003, Andriy Shapochka
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above
* copyright notice, this list of conditions and the following
* disclaimer.
*
* 2. Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials
* provided with the distribution.
*
* 3. Neither the name of the ASHWOOD nor the
* names of its contributors may be used to endorse or
* promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* ====================================================================
*
* This software consists of voluntary contributions made by
* individuals on behalf of the ASHWOOD Project and was originally
* created by Andriy Shapochka.
*
*/
package org.apache.cayenne.ashwood.graph;
import org.apache.commons.collections.ArrayStack;
import org.apache.commons.collections.CollectionUtils;
import org.apache.commons.collections.Predicate;
import org.apache.commons.collections.functors.TruePredicate;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
/**
* @since 3.1
*/
public class StrongConnection<E, V> implements Iterator<Collection<E>> {
private DigraphIteration<E, V> digraph;
private DigraphIteration<E, V> reverseDigraph;
private DigraphIteration<E, V> filteredDigraph;
private DepthFirstStampSearch<E> directDfs;
private DepthFirstSearch<E> reverseDfs;
private Set<E> seen = new HashSet<E>();
private Iterator<E> vertexIterator;
private ArrayStack dfsStack;
private DFSSeenVerticesPredicate reverseDFSFilter;
public StrongConnection(DigraphIteration<E, V> digraph) {
this.dfsStack = new ArrayStack();
this.reverseDFSFilter = new DFSSeenVerticesPredicate();
this.digraph = digraph;
this.filteredDigraph = new FilterIteration<>(digraph, new NotSeenPredicate(), TruePredicate.INSTANCE);
this.reverseDigraph = new FilterIteration<>(new ReversedIteration<>(digraph), reverseDFSFilter,
TruePredicate.INSTANCE);
this.vertexIterator = filteredDigraph.vertexIterator();
runDirectDFS();
}
@Override
public boolean hasNext() {
return !dfsStack.isEmpty();
}
@Override
public Collection<E> next() {
Collection<E> component = buildStronglyConnectedComponent();
if (dfsStack.isEmpty()) {
runDirectDFS();
}
return component;
}
@Override
public void remove() {
throw new UnsupportedOperationException("Method remove() not supported.");
}
public Digraph<Collection<E>, Collection<V>> contract(Digraph<Collection<E>, Collection<V>> contractedDigraph) {
Collection<Collection<E>> components = new ArrayList<>();
CollectionUtils.addAll(components, this);
Map<E, Collection<E>> memberToComponent = new HashMap<>();
for (Collection<E> c : components) {
for (E e : c) {
memberToComponent.put(e, c);
}
}
for (Collection<E> origin : components) {
contractedDigraph.addVertex(origin);
for (E member : origin) {
for (ArcIterator<E, V> k = digraph.outgoingIterator(member); k.hasNext();) {
V arc = k.next();
E dst = k.getDestination();
if (origin.contains(dst))
continue;
Collection<E> destination = memberToComponent.get(dst);
Collection<V> contractedArc = contractedDigraph.getArc(origin, destination);
if (contractedArc == null) {
contractedArc = Collections.singletonList(arc);
contractedDigraph.putArc(origin, destination, contractedArc);
} else {
if (contractedArc.size() == 1) {
Collection<V> tmp = contractedArc;
contractedArc = new ArrayList<>();
contractedArc.addAll(tmp);
contractedDigraph.putArc(origin, destination, contractedArc);
}
contractedArc.add(arc);
}
}
}
}
return contractedDigraph;
}
private E nextDFSRoot() {
return vertexIterator.hasNext() ? vertexIterator.next() : null;
}
private boolean runDirectDFS() {
dfsStack.clear();
reverseDFSFilter.seenVertices.clear();
E root = nextDFSRoot();
if (root == null)
return false;
if (directDfs == null)
directDfs = new DepthFirstStampSearch<>(filteredDigraph, root);
else
directDfs.reset(root);
int stamp;
E vertex;
while (directDfs.hasNext()) {
vertex = directDfs.next();
stamp = directDfs.getStamp();
if (stamp == DepthFirstStampSearch.SHRINK_STAMP || stamp == DepthFirstStampSearch.LEAF_STAMP) {
// if (seen.add(vertex)) {
dfsStack.push(vertex);
reverseDFSFilter.seenVertices.add(vertex);
// }
}
}
seen.addAll(dfsStack);
return true;
}
private Collection<E> buildStronglyConnectedComponent() {
E root = (E) dfsStack.pop();
Collection<E> component = Collections.singletonList(root);
boolean singleton = true;
if (reverseDfs == null)
reverseDfs = new DepthFirstSearch<>(reverseDigraph, root);
else
reverseDfs.reset(root);
while (reverseDfs.hasNext()) {
E vertex = reverseDfs.next();
if (vertex != root) {
if (singleton) {
Collection<E> tmp = component;
component = new ArrayList<>();
component.addAll(tmp);
singleton = false;
}
component.add(vertex);
dfsStack.remove(vertex);
}
}
reverseDFSFilter.seenVertices.removeAll(component);
return component;
}
private class DFSSeenVerticesPredicate implements Predicate {
private Set<E> seenVertices = new HashSet<>();
@Override
public boolean evaluate(Object vertex) {
return seenVertices.contains(vertex);
}
}
private class NotSeenPredicate implements Predicate {
@Override
public boolean evaluate(Object vertex) {
return !seen.contains(vertex);
}
}
}