1 files changed, 107 insertions, 0 deletions

diff --git a/subprojects/logic/src/main/java/tools/refinery/logic/literal/AbstractCountLiteral.java b/subprojects/logic/src/main/java/tools/refinery/logic/literal/AbstractCountLiteral.java
new file mode 100644
index 00000000..ee932598
--- /dev/null
+++ b/subprojects/logic/src/main/java/tools/refinery/logic/literal/AbstractCountLiteral.java
@@ -0,0 +1,107 @@
+/*
+ * SPDX-FileCopyrightText: 2023 The Refinery Authors <https://refinery.tools/>
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package tools.refinery.logic.literal;
+
+import tools.refinery.logic.Constraint;
+import tools.refinery.logic.InvalidQueryException;
+import tools.refinery.logic.equality.LiteralEqualityHelper;
+import tools.refinery.logic.equality.LiteralHashCodeHelper;
+import tools.refinery.logic.term.ConstantTerm;
+import tools.refinery.logic.term.DataVariable;
+import tools.refinery.logic.term.Variable;
+
+import java.util.List;
+import java.util.Objects;
+import java.util.Set;
+
+// {@link Object#equals(Object)} is implemented by {@link AbstractLiteral}.
+@SuppressWarnings("squid:S2160")
+public abstract class AbstractCountLiteral<T> extends AbstractCallLiteral {
+        private final Class<T> resultType;
+        private final DataVariable<T> resultVariable;
+
+        protected AbstractCountLiteral(Class<T> resultType, DataVariable<T> resultVariable, Constraint target,
+                                                                   List<Variable> arguments) {
+                super(target, arguments);
+                if (!resultVariable.getType().equals(resultType)) {
+                        throw new InvalidQueryException("Count result variable %s must be of type %s, got %s instead".formatted(
+                                        resultVariable, resultType, resultVariable.getType().getName()));
+                }
+                if (arguments.contains(resultVariable)) {
+                        throw new InvalidQueryException("Count result variable %s must not appear in the argument list"
+                                        .formatted(resultVariable));
+                }
+                this.resultType = resultType;
+                this.resultVariable = resultVariable;
+        }
+
+        public Class<T> getResultType() {
+                return resultType;
+        }
+
+        public DataVariable<T> getResultVariable() {
+                return resultVariable;
+        }
+
+        @Override
+        public Set<Variable> getOutputVariables() {
+                return Set.of(resultVariable);
+        }
+
+        protected abstract T zero();
+
+        protected abstract T one();
+
+        @Override
+        public Literal reduce() {
+                var reduction = getTarget().getReduction();
+                return switch (reduction) {
+                        case ALWAYS_FALSE -> getResultVariable().assign(new ConstantTerm<>(resultType, zero()));
+                        // The only way a constant {@code true} predicate can be called in a negative position is to have all of
+                        // its arguments bound as input variables. Thus, there will only be a single match.
+                        case ALWAYS_TRUE -> getResultVariable().assign(new ConstantTerm<>(resultType, one()));
+                        case NOT_REDUCIBLE -> this;
+                };
+        }
+
+        @Override
+        public boolean equalsWithSubstitution(LiteralEqualityHelper helper, Literal other) {
+                if (!super.equalsWithSubstitution(helper, other)) {
+                        return false;
+                }
+                var otherCountLiteral = (AbstractCountLiteral<?>) other;
+                return Objects.equals(resultType, otherCountLiteral.resultType) &&
+                                helper.variableEqual(resultVariable, otherCountLiteral.resultVariable);
+        }
+
+        @Override
+        public int hashCodeWithSubstitution(LiteralHashCodeHelper helper) {
+                return Objects.hash(super.hashCodeWithSubstitution(helper), resultType,
+                                helper.getVariableHashCode(resultVariable));
+        }
+
+        protected abstract String operatorName();
+
+        @Override
+        public String toString() {
+                var builder = new StringBuilder();
+                builder.append(resultVariable);
+                builder.append(" is ");
+                builder.append(operatorName());
+                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();
+        }
+}