1 files changed, 140 insertions, 0 deletions

diff --git a/subprojects/viatra-runtime-base-itc/src/main/java/tools/refinery/viatra/runtime/base/itc/alg/representative/RepresentativeElectionAlgorithm.java b/subprojects/viatra-runtime-base-itc/src/main/java/tools/refinery/viatra/runtime/base/itc/alg/representative/RepresentativeElectionAlgorithm.java
new file mode 100644
index 00000000..51015404
--- /dev/null
+++ b/subprojects/viatra-runtime-base-itc/src/main/java/tools/refinery/viatra/runtime/base/itc/alg/representative/RepresentativeElectionAlgorithm.java
@@ -0,0 +1,140 @@
+/*
+ * SPDX-FileCopyrightText: 2023 The Refinery Authors <https://refinery.tools/>
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package tools.refinery.viatra.runtime.base.itc.alg.representative;
+
+import tools.refinery.viatra.runtime.base.itc.graphimpl.Graph;
+import tools.refinery.viatra.runtime.base.itc.igraph.IGraphObserver;
+import tools.refinery.viatra.runtime.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(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);
+        }
+}