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Implemented: Add a generic directed graph utilitary class

(OFBIZ-11275)
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Samuel Trégouët authored and mthl committed Oct 30, 2019
1 parent 1317703 commit 7044af8a6fe9261f4fc5806fd6fefd9e537ee5be
@@ -207,6 +207,8 @@ dependencies {
testImplementation 'org.hamcrest:hamcrest:2.1'
testImplementation 'org.hamcrest:hamcrest-library:2.1' // Enable junit4 to not depend on hamcrest-1.3
testImplementation 'org.mockito:mockito-core:3.1.0'
testImplementation 'com.pholser:junit-quickcheck-core:0.9'
testImplementation 'com.pholser:junit-quickcheck-generators:0.9'
runtimeOnly 'javax.xml.soap:javax.xml.soap-api:1.4.0'
runtimeOnly 'de.odysseus.juel:juel-spi:2.2.7'
runtimeOnly 'net.sf.barcode4j:barcode4j-fop-ext:2.1'
@@ -109,7 +109,10 @@ under the License.
<module name="SimplifyBooleanReturn"/>

<!-- Checks for class design -->
<module name="DesignForExtension"/>
<module name="DesignForExtension">
<property name="ignoredAnnotations"
value="After, AfterClass, Before, BeforeClass, Test, Property"/>
</module>
<module name="FinalClass"/>
<module name="HideUtilityClassConstructor"/>
<module name="InterfaceIsType"/>
@@ -0,0 +1,118 @@
/*
* 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.ofbiz.base.util;

import static java.util.stream.Collectors.toSet;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

/**
* A basic directed graph utilitary.
* <p>
* A directed graph is a data structure consisting of nodes and arrows connecting those nodes
* which are called <em>edges</em>. In a directed graph edges are ordered pairs of respectively
* source and target nodes.
* <p>
* This implementation is adapted to small in-memory graphs.
*
* @param <T> the type of the nodes
* @see <a href="https://www.wikipedia.org/wiki/Directed_graph">Directed graph</a>
*/
public class Digraph<T> {
/** The map associating source nodes to their adjacent target nodes. */
private final Map<T, Collection<T>> edges;
/** The set of nodes */
private final Set<T> nodes;

/**
* Constructs a directed graph from a specification Map.
*
* @param spec the map defining a set of source nodes (keys) that are linked to a collection
* of adjacent target nodes (values). Both keys and values must not be {@code null}.
* @throws IllegalArgumentException when a target node is not present in the sources nodes.
*/
public Digraph(Map<T, Collection<T>> spec) throws IllegalArgumentException {
this.edges = spec;
this.nodes = spec.keySet();
// Check that all adjacent nodes are present as keys in the map.
Set<T> undeclaredNodes = spec.values().stream()
.flatMap(Collection::stream)
.filter(child -> !nodes.contains(child))
.collect(toSet());
if (!undeclaredNodes.isEmpty()) {
String msg = String.format("%s nodes are not present in the graph", undeclaredNodes);
throw new IllegalArgumentException(msg);
}
}

/**
* Sort nodes in a topological ordering assuming that this graph is acyclic.
* <p>
* A graph without cycles is often called a <em>Directed Acyclic Graph</em> (DAG).
*
* @return a linear ordering of nodes such for every edge in the graph its target node
* is present before its source node.
* @throws IllegalStateException when this graph contains a cycle.
* @see <a href="https://www.wikipedia.org/wiki/Topological_sorting">topological sorting</a>
* @see <a href="https://www.wikipedia.org/wiki/Directed_acyclic_graph">DAG</a>
*/
public List<T> sort() throws IllegalStateException {
Set<T> permanents = new HashSet<>();
Set<T> temporaries = new HashSet<>();
List<T> result = new ArrayList<>();
for (T node : nodes) {
if (!permanents.contains(node)) {
visit(result, node, permanents, temporaries);
}
}
return result;
}

/**
* Traverses the graph using <em>Depth First Search</em> (DFS) to construct a topological ordering.
*
* @param res the ordered list that we are building
* @param root the current node we are visiting
* @param permanents the nodes that have been successfully been visited
* @param temporaries the nodes that we have started to visit but might contain cycles.
* @throws IllegalStateException when a cycle is found.
* @see #sort
* @see <a href="https://www.wikipedia.org/wiki/Depth-first_search">Depth Dirst Search</a>
*/
private void visit(List<T> res, T root, Set<T> permanents, Set<T> temporaries) throws IllegalStateException {
if (permanents.contains(root)) {
return;
} else if (temporaries.contains(root)) {
throw new IllegalStateException("A cycle has been found");
} else {
temporaries.add(root);
for (T next : edges.get(root)) {
visit(res, next, permanents, temporaries);
}
temporaries.remove(root);
permanents.add(root);
res.add(root);
}
}
}
@@ -0,0 +1,93 @@
/*
* 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.ofbiz.base.util;

import static java.util.Arrays.asList;
import static java.util.Collections.emptyList;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.in;
import static org.hamcrest.Matchers.is;
import static org.junit.Assume.assumeNoException;

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Map;

import org.junit.Test;
import org.junit.runner.RunWith;

import com.pholser.junit.quickcheck.Property;
import com.pholser.junit.quickcheck.runner.JUnitQuickcheck;

@RunWith(JUnitQuickcheck.class)
public class DiGraphTest {

@Test
public void testAcyclic() {
checkTopologicalOrder(UtilMisc.toMap(
"a", asList("b"),
"b", asList("c", "d"),
"c", emptyList(),
"d", emptyList(),
"z", emptyList(),
"f", emptyList(),
"e", asList("z", "b")));
}

@Test(expected = IllegalStateException.class)
public void testWithCycle() {
Map<String, Collection<String>> g = UtilMisc.toMap(
"a", asList("b"),
"b", asList("c"),
"c", asList("a"));
Digraph<String> dg = new Digraph<>(g);
dg.sort();
}

@Test
public void testMultipleParents() {
checkTopologicalOrder(UtilMisc.toMap(
"a", asList("b"),
"b", emptyList(),
"c", asList("b")));
}

@Property
public <T> void topologicalOrderProperty(Map<T, Collection<T>> graphspec) {
try {
checkTopologicalOrder(graphspec);
} catch (IllegalArgumentException e) {
assumeNoException("Invalid Graph", e);
} catch (IllegalStateException e) {
assumeNoException("Not a directed acyclic graph", e);
}
}

private static <T> void checkTopologicalOrder(Map<T, Collection<T>> graphspec) {
Digraph<T> g = new Digraph<>(graphspec);
List<T> seen = new ArrayList<>();
for (T node : g.sort()) {
for (T adjacent : graphspec.get(node)) {
assertThat("child nodes are before their parents", adjacent, is(in(seen)));
}
seen.add(node);
}
}
}

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