Move check to util class

Signed-off-by: Vijayan Balasubramanian <[email protected]>

src/main/java/org/opensearch/knn/index/mapper/KNNVectorFieldMapper.java

@@ -58,6 +58,7 @@
 import static org.opensearch.knn.index.mapper.KNNVectorFieldMapperUtil.createKNNMethodContextFromLegacy;
 import static org.opensearch.knn.index.mapper.KNNVectorFieldMapperUtil.createStoredFieldForByteVector;
 import static org.opensearch.knn.index.mapper.KNNVectorFieldMapperUtil.createStoredFieldForFloatVector;
+import static org.opensearch.knn.index.mapper.KNNVectorFieldMapperUtil.useKNNMethodContextFromLegacy;
 import static org.opensearch.knn.index.mapper.KNNVectorFieldMapperUtil.validateIfCircuitBreakerIsNotTriggered;
 import static org.opensearch.knn.index.mapper.KNNVectorFieldMapperUtil.validateIfKNNPluginEnabled;
 import static org.opensearch.knn.index.mapper.ModelFieldMapper.UNSET_MODEL_DIMENSION_IDENTIFIER;
@@ -500,7 +501,7 @@ private void resolveKNNMethodComponents(
                     .build()
             );
 
-            if (useKNNMethodContextFromLegacy(builder, parserContext)) {
+            if (useKNNMethodContextFromLegacy(builder.originalParameters, parserContext)) {
                 // Then create KNNMethodContext to be used from the legacy index settings
                 builder.originalParameters.setResolvedKnnMethodContext(
                     createKNNMethodContextFromLegacy(parserContext.getSettings(), parserContext.indexVersionCreated(), resolvedSpaceType)
@@ -549,12 +550,6 @@ private void setEngine(final KNNMethodContext knnMethodContext, KNNEngine knnEng
         }
     }
 
-    static boolean useKNNMethodContextFromLegacy(Builder builder, Mapper.TypeParser.ParserContext parserContext) {
-        // If the original parameters are from legacy, and it is created on or before 2_17_2 since default is changed to
-        // FAISS starting 2_18, which doesn't support accepting algo params from index settings
-        return parserContext.indexVersionCreated().onOrBefore(Version.V_2_17_2) && builder.originalParameters.isLegacyMapping();
-    }
-
     // We store the version of the index with the mapper as different version of Opensearch has different default
     // values of KNN engine Algorithms hyperparameters.
     protected Version indexCreatedVersion;

src/main/java/org/opensearch/knn/index/mapper/KNNVectorFieldMapperUtil.java

@@ -20,6 +20,7 @@
 import org.apache.lucene.util.BytesRef;
 import org.opensearch.Version;
 import org.opensearch.common.settings.Settings;
+import org.opensearch.index.mapper.Mapper;
 import org.opensearch.knn.index.KNNSettings;
 import org.opensearch.knn.index.KnnCircuitBreakerException;
 import org.opensearch.knn.index.SpaceType;
@@ -193,6 +194,15 @@ private static int getEfConstruction(Settings indexSettings, Version indexVersio
         return Integer.parseInt(efConstruction);
     }
 
+    static boolean useKNNMethodContextFromLegacy(
+        OriginalMappingParameters originalMappingParameters,
+        Mapper.TypeParser.ParserContext parserContext
+    ) {
+        // If the original parameters are from legacy, and it is created on or before 2_17_2 since default is changed to
+        // FAISS starting 2_18, which doesn't support accepting algo params from index settings
+        return parserContext.indexVersionCreated().onOrBefore(Version.V_2_17_2) && originalMappingParameters.isLegacyMapping();
+    }
+
     static KNNMethodContext createKNNMethodContextFromLegacy(
         Settings indexSettings,
         Version indexCreatedVersion,

src/test/java/org/opensearch/knn/index/mapper/KNNVectorFieldMapperTests.java

@@ -286,8 +286,13 @@ public void testTypeParser_withDifferentSpaceTypeCombinations_thenSuccess() thro
         assertTrue(knnVectorFieldMapper.fieldType().getKnnMappingConfig().getModelId().isEmpty());
 
         // mock useKNNMethodContextFromLegacy to simulate index ix created before 2_18
-        try (MockedStatic<KNNVectorFieldMapper> utilMockedStatic = Mockito.mockStatic(KNNVectorFieldMapper.class)) {
-            utilMockedStatic.when(() -> KNNVectorFieldMapper.useKNNMethodContextFromLegacy(any(), any())).thenReturn(true);
+        try (
+            MockedStatic<KNNVectorFieldMapperUtil> utilMockedStatic = Mockito.mockStatic(
+                KNNVectorFieldMapperUtil.class,
+                Mockito.CALLS_REAL_METHODS
+            )
+        ) {
+            utilMockedStatic.when(() -> KNNVectorFieldMapperUtil.useKNNMethodContextFromLegacy(any(), any())).thenReturn(true);
             // if space type is provided and legacy mappings is hit
             xContentBuilder = XContentFactory.jsonBuilder()
                 .startObject()