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/*
* SPDX-FileCopyrightText: 2023 The Refinery Authors <https://refinery.tools/>
*
* SPDX-License-Identifier: EPL-2.0
*/
package tools.refinery.interpreter.rete.itc.alg.representative;
import tools.refinery.interpreter.rete.itc.graphimpl.Graph;
import tools.refinery.interpreter.rete.itc.igraph.IGraphObserver;
import tools.refinery.interpreter.matchers.util.Direction;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
public abstract class RepresentativeElectionAlgorithm implements IGraphObserver<Object> {
protected final Graph<Object> graph;
protected final Map<Object, Object> representatives = new HashMap<>();
protected final Map<Object, Set<Object>> components = new HashMap<>();
private RepresentativeObserver observer;
protected RepresentativeElectionAlgorithm(Graph<Object> graph) {
this.graph = graph;
initializeComponents();
graph.attachObserver(this);
}
protected abstract void initializeComponents();
protected void initializeSet(Set<Object> set) {
var iterator = set.iterator();
if (!iterator.hasNext()) {
// Set is empty.
return;
}
var representative = iterator.next();
for (var node : set) {
var oldRepresentative = representatives.put(node, representative);
if (oldRepresentative != null && !representative.equals(oldRepresentative)) {
throw new IllegalStateException("Node %s is already in a set represented by %s, cannot add it to %s"
.formatted(node, oldRepresentative, set));
}
}
components.put(representative, set);
}
protected void merge(Set<Object> toMerge) {
if (toMerge.isEmpty()) {
return;
}
var representativesToMerge = new HashSet<>();
Object bestRepresentative = null;
Set<Object> bestSet = null;
for (var object : toMerge) {
var representative = getRepresentative(object);
if (representativesToMerge.add(representative)) {
var component = getComponent(representative);
if (bestSet == null || bestSet.size() < component.size()) {
bestRepresentative = representative;
bestSet = component;
}
}
}
if (bestRepresentative == null) {
throw new AssertionError("Could not determine best representative");
}
for (var representative : representativesToMerge) {
if (!bestRepresentative.equals(representative)) {
components.remove(representative);
}
}
components.put(bestRepresentative, toMerge);
for (var object : toMerge) {
var previousRepresentative = representatives.put(object, bestRepresentative);
if (!bestSet.contains(object)) {
notifyToObservers(object, previousRepresentative, bestRepresentative);
}
}
}
protected void merge(Object leftRepresentative, Object rightRepresentative) {
if (leftRepresentative.equals(rightRepresentative)) {
return;
}
var leftSet = getComponent(leftRepresentative);
var rightSet = getComponent(rightRepresentative);
if (leftSet.size() < rightSet.size()) {
merge(rightRepresentative, rightSet, leftRepresentative, leftSet);
} else {
merge(leftRepresentative, leftSet, rightRepresentative, rightSet);
}
}
private void merge(Object preservedRepresentative, Set<Object> preservedSet, Object removedRepresentative,
Set<Object> removedSet) {
components.remove(removedRepresentative);
for (var node : removedSet) {
representatives.put(node, preservedRepresentative);
preservedSet.add(node);
notifyToObservers(node, removedRepresentative, preservedRepresentative);
}
}
protected void assignNewRepresentative(Object oldRepresentative, Set<Object> set) {
var iterator = set.iterator();
if (!iterator.hasNext()) {
return;
}
var newRepresentative = iterator.next();
components.put(newRepresentative, set);
for (var node : set) {
var oldRepresentativeOfNode = representatives.put(node, newRepresentative);
if (!oldRepresentative.equals(oldRepresentativeOfNode)) {
throw new IllegalArgumentException("Node %s was not represented by %s but by %s"
.formatted(node, oldRepresentative, oldRepresentativeOfNode));
}
notifyToObservers(node, oldRepresentative, newRepresentative);
}
}
public void setObserver(RepresentativeObserver observer) {
this.observer = observer;
}
public Map<Object, Set<Object>> getComponents() {
return components;
}
public Object getRepresentative(Object node) {
return representatives.get(node);
}
public Set<Object> getComponent(Object representative) {
return components.get(representative);
}
public void dispose() {
graph.detachObserver(this);
}
@Override
public void nodeInserted(Object n) {
var component = new HashSet<>(1);
component.add(n);
initializeSet(component);
notifyToObservers(n, n, Direction.INSERT);
}
@Override
public void nodeDeleted(Object n) {
var representative = representatives.remove(n);
if (!representative.equals(n)) {
throw new IllegalStateException("Trying to delete node with dangling edges");
}
components.remove(representative);
notifyToObservers(n, representative, Direction.DELETE);
}
protected void notifyToObservers(Object node, Object oldRepresentative, Object newRepresentative) {
notifyToObservers(node, oldRepresentative, Direction.DELETE);
notifyToObservers(node, newRepresentative, Direction.INSERT);
}
protected void notifyToObservers(Object node, Object representative, Direction direction) {
if (observer != null) {
observer.tupleChanged(node, representative, direction);
}
}
public interface Factory {
RepresentativeElectionAlgorithm create(Graph<Object> graph);
}
}
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