refactor: use Cursor in query result sets

6 files changed, 94 insertions, 17 deletions

diff --git a/subprojects/store-query-viatra/src/main/java/tools/refinery/store/query/viatra/internal/pquery/RawPatternMatcher.java b/subprojects/store-query-viatra/src/main/java/tools/refinery/store/query/viatra/internal/pquery/RawPatternMatcher.java
index 8f56586e..5924ff15 100644
--- a/subprojects/store-query-viatra/src/main/java/tools/refinery/store/query/viatra/internal/pquery/RawPatternMatcher.java
+++ b/subprojects/store-query-viatra/src/main/java/tools/refinery/store/query/viatra/internal/pquery/RawPatternMatcher.java
@@ -9,13 +9,13 @@ import org.eclipse.viatra.query.runtime.matchers.tuple.TupleMask;
 import org.eclipse.viatra.query.runtime.matchers.tuple.Tuples;
 import org.eclipse.viatra.query.runtime.rete.index.Indexer;
 import org.eclipse.viatra.query.runtime.rete.matcher.RetePatternMatcher;
+import tools.refinery.store.map.Cursor;
+import tools.refinery.store.map.Cursors;
 import tools.refinery.store.query.ResultSet;
 import tools.refinery.store.query.viatra.ViatraTupleLike;
 import tools.refinery.store.tuple.Tuple;
 import tools.refinery.store.tuple.TupleLike;
 
-import java.util.stream.Stream;
-
 /**
  * Directly access the tuples inside a VIATRA pattern matcher.<p>
  * This class neglects calling
@@ -64,12 +64,12 @@ public class RawPatternMatcher extends GenericPatternMatcher implements ResultSe
     }
 
     @Override
-    public Stream<TupleLike> allResults() {
+    public Cursor<TupleLike, Boolean> allResults() {
         if (emptyMaskIndexer == null) {
-            return backend.getAllMatches(empty).map(ViatraTupleLike::new);
+            return new ResultSetCursor(backend.getAllMatches(empty).iterator());
         }
         var matches = emptyMaskIndexer.get(Tuples.staticArityFlatTupleOf());
-        return matches == null ? Stream.of() : matches.stream().map(ViatraTupleLike::new);
+        return matches == null ? Cursors.empty() : new ResultSetCursor(matches.stream().iterator());
     }
 
     @Override
diff --git a/subprojects/store-query-viatra/src/main/java/tools/refinery/store/query/viatra/internal/pquery/ResultSetCursor.java b/subprojects/store-query-viatra/src/main/java/tools/refinery/store/query/viatra/internal/pquery/ResultSetCursor.java
new file mode 100644
index 00000000..5e6d1970
--- /dev/null
+++ b/subprojects/store-query-viatra/src/main/java/tools/refinery/store/query/viatra/internal/pquery/ResultSetCursor.java
@@ -0,0 +1,43 @@
+package tools.refinery.store.query.viatra.internal.pquery;
+
+import org.eclipse.viatra.query.runtime.matchers.tuple.ITuple;
+import tools.refinery.store.map.Cursor;
+import tools.refinery.store.query.viatra.ViatraTupleLike;
+import tools.refinery.store.tuple.TupleLike;
+
+import java.util.Iterator;
+
+class ResultSetCursor implements Cursor<TupleLike, Boolean> {
+    private final Iterator<? extends ITuple> tuplesIterator;
+    private boolean terminated;
+    private TupleLike key;
+
+    public ResultSetCursor(Iterator<? extends ITuple> tuplesIterator) {
+        this.tuplesIterator = tuplesIterator;
+    }
+
+    @Override
+    public TupleLike getKey() {
+        return key;
+    }
+
+    @Override
+    public Boolean getValue() {
+        return true;
+    }
+
+    @Override
+    public boolean isTerminated() {
+        return terminated;
+    }
+
+    @Override
+    public boolean move() {
+        if (!terminated && tuplesIterator.hasNext()) {
+            key = new ViatraTupleLike(tuplesIterator.next());
+            return true;
+        }
+        terminated = true;
+        return false;
+    }
+}
diff --git a/subprojects/store-query-viatra/src/test/java/tools/refinery/store/query/viatra/QueryTest.java b/subprojects/store-query-viatra/src/test/java/tools/refinery/store/query/viatra/QueryTest.java
index 3dd517c4..8b25419d 100644
--- a/subprojects/store-query-viatra/src/test/java/tools/refinery/store/query/viatra/QueryTest.java
+++ b/subprojects/store-query-viatra/src/test/java/tools/refinery/store/query/viatra/QueryTest.java
@@ -1,6 +1,7 @@
 package tools.refinery.store.query.viatra;
 
 import org.junit.jupiter.api.Test;
+import tools.refinery.store.map.Cursor;
 import tools.refinery.store.model.ModelStore;
 import tools.refinery.store.query.Dnf;
 import tools.refinery.store.query.ModelQuery;
@@ -14,7 +15,6 @@ import tools.refinery.store.tuple.TupleLike;
 
 import java.util.HashSet;
 import java.util.Set;
-import java.util.stream.Stream;
 
 import static org.junit.jupiter.api.Assertions.*;
 import static tools.refinery.store.query.literal.Literals.not;
@@ -712,11 +712,10 @@ class QueryTest {
                 assertThrows(IllegalArgumentException.class, () -> queryBuilder.queries(predicate));
         }
 
-        static void compareMatchSets(Stream<TupleLike> matchSet, Set<Tuple> expected) {
+        private static void compareMatchSets(Cursor<TupleLike, Boolean> cursor, Set<Tuple> expected) {
                 Set<Tuple> translatedMatchSet = new HashSet<>();
-                var iterator = matchSet.iterator();
-                while (iterator.hasNext()) {
-                        var element = iterator.next();
+                while (cursor.move()) {
+                        var element = cursor.getKey();
                         translatedMatchSet.add(element.toTuple());
                 }
                 assertEquals(expected, translatedMatchSet);
diff --git a/subprojects/store-query/src/main/java/tools/refinery/store/query/EmptyResultSet.java b/subprojects/store-query/src/main/java/tools/refinery/store/query/EmptyResultSet.java
index 0c2e07d6..9ff6df26 100644
--- a/subprojects/store-query/src/main/java/tools/refinery/store/query/EmptyResultSet.java
+++ b/subprojects/store-query/src/main/java/tools/refinery/store/query/EmptyResultSet.java
@@ -1,9 +1,9 @@
 package tools.refinery.store.query;
 
+import tools.refinery.store.map.Cursor;
+import tools.refinery.store.map.Cursors;
 import tools.refinery.store.tuple.TupleLike;
 
-import java.util.stream.Stream;
-
 public class EmptyResultSet implements ResultSet {
         @Override
         public boolean hasResult(TupleLike parameters) {
@@ -11,8 +11,8 @@ public class EmptyResultSet implements ResultSet {
         }
 
         @Override
-        public Stream<TupleLike> allResults() {
-                return Stream.of();
+        public Cursor<TupleLike, Boolean> allResults() {
+                return Cursors.empty();
         }
 
         @Override
diff --git a/subprojects/store-query/src/main/java/tools/refinery/store/query/ResultSet.java b/subprojects/store-query/src/main/java/tools/refinery/store/query/ResultSet.java
index 407cf075..d2b8c9dd 100644
--- a/subprojects/store-query/src/main/java/tools/refinery/store/query/ResultSet.java
+++ b/subprojects/store-query/src/main/java/tools/refinery/store/query/ResultSet.java
@@ -1,9 +1,8 @@
 package tools.refinery.store.query;
 
+import tools.refinery.store.map.Cursor;
 import tools.refinery.store.tuple.TupleLike;
 
-import java.util.stream.Stream;
-
 public interface ResultSet {
         default boolean hasResult() {
                 return countResults() > 0;
@@ -11,7 +10,7 @@ public interface ResultSet {
 
         boolean hasResult(TupleLike parameters);
 
-        Stream<TupleLike> allResults();
+        Cursor<TupleLike, Boolean> allResults();
 
         int countResults();
 }
diff --git a/subprojects/store/src/main/java/tools/refinery/store/map/Cursors.java b/subprojects/store/src/main/java/tools/refinery/store/map/Cursors.java
new file mode 100644
index 00000000..fc8e628b
--- /dev/null
+++ b/subprojects/store/src/main/java/tools/refinery/store/map/Cursors.java
@@ -0,0 +1,36 @@
+package tools.refinery.store.map;
+
+public final class Cursors {
+    private Cursors() {
+        throw new IllegalStateException("This is a static utility class and should not be instantiated directly");
+    }
+
+    public static <K, V> Cursor<K, V> empty() {
+        return new Empty<>();
+    }
+
+    private static class Empty<K, V> implements Cursor<K, V> {
+        private boolean terminated = false;
+
+        @Override
+        public K getKey() {
+            return null;
+        }
+
+        @Override
+        public V getValue() {
+            return null;
+        }
+
+        @Override
+        public boolean isTerminated() {
+            return terminated;
+        }
+
+        @Override
+        public boolean move() {
+            terminated = true;
+            return false;
+        }
+    }
+}