1 files changed, 119 insertions, 0 deletions

diff --git a/subprojects/store-query/src/main/java/tools/refinery/store/query/literal/RepresentativeElectionLiteral.java b/subprojects/store-query/src/main/java/tools/refinery/store/query/literal/RepresentativeElectionLiteral.java
new file mode 100644
index 00000000..f7323947
--- /dev/null
+++ b/subprojects/store-query/src/main/java/tools/refinery/store/query/literal/RepresentativeElectionLiteral.java
@@ -0,0 +1,119 @@
+/*
+ * SPDX-FileCopyrightText: 2023 The Refinery Authors <https://refinery.tools/>
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package tools.refinery.store.query.literal;
+
+import tools.refinery.store.query.Constraint;
+import tools.refinery.store.query.InvalidQueryException;
+import tools.refinery.store.query.equality.LiteralEqualityHelper;
+import tools.refinery.store.query.equality.LiteralHashCodeHelper;
+import tools.refinery.store.query.substitution.Substitution;
+import tools.refinery.store.query.term.NodeVariable;
+import tools.refinery.store.query.term.ParameterDirection;
+import tools.refinery.store.query.term.Variable;
+
+import java.util.List;
+import java.util.Set;
+
+// {@link Object#equals(Object)} is implemented by {@link AbstractLiteral}.
+@SuppressWarnings("squid:S2160")
+public class RepresentativeElectionLiteral extends AbstractCallLiteral {
+        private final Connectivity connectivity;
+
+        public RepresentativeElectionLiteral(Connectivity connectivity, Constraint target, NodeVariable specific,
+                                                                                 NodeVariable representative) {
+                this(connectivity, target, List.of(specific, representative));
+        }
+
+        private RepresentativeElectionLiteral(Connectivity connectivity, Constraint target, List<Variable> arguments) {
+                super(target, arguments);
+                this.connectivity = connectivity;
+                var parameters = target.getParameters();
+                int arity = target.arity();
+                if (arity != 2) {
+                        throw new InvalidQueryException("SCCs can only take binary relations");
+                }
+                if (parameters.get(0).isDataVariable() || parameters.get(1).isDataVariable()) {
+                        throw new InvalidQueryException("SCCs can only be computed over nodes");
+                }
+                if (parameters.get(0).getDirection() != ParameterDirection.OUT ||
+                                parameters.get(1).getDirection() != ParameterDirection.OUT) {
+                        throw new InvalidQueryException("SCCs cannot take input parameters");
+                }
+        }
+
+        public Connectivity getConnectivity() {
+                return connectivity;
+        }
+
+        @Override
+        protected Literal doSubstitute(Substitution substitution, List<Variable> substitutedArguments) {
+                return new RepresentativeElectionLiteral(connectivity, getTarget(), substitutedArguments);
+        }
+
+        @Override
+        public Set<Variable> getOutputVariables() {
+                return getArgumentsOfDirection(ParameterDirection.OUT);
+        }
+
+        @Override
+        public Set<Variable> getInputVariables(Set<? extends Variable> positiveVariablesInClause) {
+                return Set.of();
+        }
+
+        @Override
+        public Set<Variable> getPrivateVariables(Set<? extends Variable> positiveVariablesInClause) {
+                return Set.of();
+        }
+
+        @Override
+        public Literal reduce() {
+                var reduction = getTarget().getReduction();
+                return switch (reduction) {
+                        case ALWAYS_FALSE -> BooleanLiteral.FALSE;
+                        case ALWAYS_TRUE -> throw new InvalidQueryException(
+                                        "Trying to elect representatives over an infinite set");
+                        case NOT_REDUCIBLE -> this;
+                };
+        }
+
+        @Override
+        public AbstractCallLiteral withArguments(Constraint newTarget, List<Variable> newArguments) {
+                return new RepresentativeElectionLiteral(connectivity, newTarget, newArguments);
+        }
+
+        @Override
+        public boolean equalsWithSubstitution(LiteralEqualityHelper helper, Literal other) {
+                if (!super.equalsWithSubstitution(helper, other)) {
+                        return false;
+                }
+                var otherRepresentativeElectionLiteral = (RepresentativeElectionLiteral) other;
+                return connectivity.equals(otherRepresentativeElectionLiteral.connectivity);
+        }
+
+        @Override
+        public int hashCodeWithSubstitution(LiteralHashCodeHelper helper) {
+                return super.hashCodeWithSubstitution(helper) * 31 + connectivity.hashCode();
+        }
+
+        @Override
+        public String toString() {
+                var builder = new StringBuilder();
+                builder.append("@Representative(\"");
+                builder.append(connectivity);
+                builder.append("\") ");
+                builder.append(getTarget().toReferenceString());
+                builder.append("(");
+                var argumentIterator = getArguments().iterator();
+                if (argumentIterator.hasNext()) {
+                        builder.append(argumentIterator.next());
+                        while (argumentIterator.hasNext()) {
+                                builder.append(", ").append(argumentIterator.next());
+                        }
+                }
+                builder.append(")");
+                return builder.toString();
+        }
+}