1 files changed, 48 insertions, 0 deletions

diff --git a/subprojects/store-query-viatra/src/main/java/tools/refinery/store/query/viatra/internal/matcher/IndexerUtils.java b/subprojects/store-query-viatra/src/main/java/tools/refinery/store/query/viatra/internal/matcher/IndexerUtils.java
new file mode 100644
index 00000000..55eb8c44
--- /dev/null
+++ b/subprojects/store-query-viatra/src/main/java/tools/refinery/store/query/viatra/internal/matcher/IndexerUtils.java
@@ -0,0 +1,48 @@
+package tools.refinery.store.query.viatra.internal.matcher;
+
+import org.eclipse.viatra.query.runtime.matchers.tuple.TupleMask;
+import org.eclipse.viatra.query.runtime.rete.index.Indexer;
+import org.eclipse.viatra.query.runtime.rete.matcher.ReteEngine;
+import org.eclipse.viatra.query.runtime.rete.matcher.RetePatternMatcher;
+import org.eclipse.viatra.query.runtime.rete.traceability.RecipeTraceInfo;
+
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
+
+final class IndexerUtils {
+    private static final MethodHandle GET_ENGINE_HANDLE;
+    private static final MethodHandle GET_PRODUCTION_NODE_TRACE_HANDLE;
+    private static final MethodHandle ACCESS_PROJECTION_HANDLE;
+
+    static {
+        try {
+            var lookup = MethodHandles.privateLookupIn(RetePatternMatcher.class, MethodHandles.lookup());
+            GET_ENGINE_HANDLE = lookup.findGetter(RetePatternMatcher.class, "engine", ReteEngine.class);
+            GET_PRODUCTION_NODE_TRACE_HANDLE = lookup.findGetter(RetePatternMatcher.class, "productionNodeTrace",
+                    RecipeTraceInfo.class);
+            ACCESS_PROJECTION_HANDLE = lookup.findVirtual(ReteEngine.class, "accessProjection",
+                    MethodType.methodType(Indexer.class, RecipeTraceInfo.class, TupleMask.class));
+        } catch (IllegalAccessException | NoSuchFieldException | NoSuchMethodException e) {
+            throw new IllegalStateException("Cannot access private members of %s"
+                    .formatted(RetePatternMatcher.class.getPackageName()), e);
+        }
+    }
+
+    private IndexerUtils() {
+        throw new IllegalStateException("This is a static utility class and should not be instantiated directly");
+    }
+
+    public static Indexer getIndexer(RetePatternMatcher backend, TupleMask mask) {
+        try {
+            var engine = (ReteEngine) GET_ENGINE_HANDLE.invokeExact(backend);
+            var trace = (RecipeTraceInfo) GET_PRODUCTION_NODE_TRACE_HANDLE.invokeExact(backend);
+            return (Indexer) ACCESS_PROJECTION_HANDLE.invokeExact(engine, trace, mask);
+        } catch (Error e) {
+            // Fatal JVM errors should not be wrapped.
+            throw e;
+        } catch (Throwable e) {
+            throw new IllegalStateException("Cannot access matcher for mask " + mask, e);
+        }
+    }
+}