Common interfaces for diff computation

Signed-off-by: Bukhtawar Khan <bukhtawa@amazon.com>

server/src/main/java/org/opensearch/cluster/routing/RoutingTable.java

@@ -407,7 +407,7 @@ public void writeTo(StreamOutput out) throws IOException {
         }
     }
 
-    private static class RoutingTableDiff implements Diff<RoutingTable> {
+    private static class RoutingTableDiff implements Diff<RoutingTable>, StringKeyDiffProvider<IndexRoutingTable> {
 
         private final long version;
 
@@ -436,6 +436,11 @@ public void writeTo(StreamOutput out) throws IOException {
             out.writeLong(version);
             indicesRouting.writeTo(out);
         }
+
+        @Override
+        public DiffableUtils.MapDiff<String, IndexRoutingTable, Map<String, IndexRoutingTable>> provideDiff() {
+            return (DiffableUtils.MapDiff<String, IndexRoutingTable, Map<String, IndexRoutingTable>>) indicesRouting;
+        }
     }
 
     public static Builder builder() {

server/src/main/java/org/opensearch/cluster/routing/RoutingTableIncrementalDiff.java

@@ -15,16 +15,16 @@
 import org.opensearch.core.index.Index;
 
 import java.io.IOException;
-import java.util.Collections;
-import java.util.HashMap;
 import java.util.Map;
 
+import static org.opensearch.cluster.DiffableUtils.MapDiff;
+
 /**
  * Represents a difference between {@link RoutingTable} objects that can be serialized and deserialized.
  */
-public class RoutingTableIncrementalDiff implements Diff<RoutingTable> {
+public class RoutingTableIncrementalDiff implements Diff<RoutingTable>, StringKeyDiffProvider<IndexRoutingTable> {
 
-    private DiffableUtils.MapDiff<String, IndexRoutingTable, Map<String, IndexRoutingTable>> indicesRouting;
+    private final Diff<Map<String, IndexRoutingTable>> indicesRouting;
 
     private final long version;
 
@@ -77,8 +77,9 @@ public void writeTo(StreamOutput out) throws IOException {
         indicesRouting.writeTo(out);
     }
 
-    public DiffableUtils.MapDiff<String, IndexRoutingTable, Map<String, IndexRoutingTable>> getIndicesRouting() {
-        return indicesRouting;
+    @Override
+    public MapDiff<String, IndexRoutingTable, Map<String, IndexRoutingTable>> provideDiff() {
+        return (MapDiff<String, IndexRoutingTable, Map<String, IndexRoutingTable>>) indicesRouting;
     }
 
     /**

server/src/main/java/org/opensearch/cluster/routing/remote/InternalRemoteRoutingTableService.java

@@ -17,6 +17,7 @@
 import org.opensearch.cluster.routing.IndexRoutingTable;
 import org.opensearch.cluster.routing.RoutingTable;
 import org.opensearch.cluster.routing.RoutingTableIncrementalDiff;
+import org.opensearch.cluster.routing.StringKeyDiffProvider;
 import org.opensearch.common.blobstore.BlobPath;
 import org.opensearch.common.lifecycle.AbstractLifecycleComponent;
 import org.opensearch.common.remote.RemoteWritableEntityStore;
@@ -97,11 +98,12 @@ public List<IndexRoutingTable> getIndicesRouting(RoutingTable routingTable) {
      * @param after  current routing table
      * @return incremental diff of the previous and current routing table
      */
-    public DiffableUtils.MapDiff<String, IndexRoutingTable, Map<String, IndexRoutingTable>> getIndicesRoutingMapDiff(
+    @Override
+    public StringKeyDiffProvider<IndexRoutingTable> getIndicesRoutingMapDiff(
         RoutingTable before,
         RoutingTable after
     ) {
-        return new RoutingTableIncrementalDiff(before, after).getIndicesRouting();
+        return new RoutingTableIncrementalDiff(before, after);
     }
 
     /**

server/src/main/java/org/opensearch/cluster/routing/remote/NoopRemoteRoutingTableService.java

@@ -10,16 +10,15 @@
 
 import org.opensearch.action.LatchedActionListener;
 import org.opensearch.cluster.Diff;
-import org.opensearch.cluster.DiffableUtils;
 import org.opensearch.cluster.routing.IndexRoutingTable;
 import org.opensearch.cluster.routing.RoutingTable;
 import org.opensearch.cluster.routing.RoutingTableIncrementalDiff;
+import org.opensearch.cluster.routing.StringKeyDiffProvider;
 import org.opensearch.common.lifecycle.AbstractLifecycleComponent;
 import org.opensearch.gateway.remote.ClusterMetadataManifest;
 
 import java.io.IOException;
 import java.util.List;
-import java.util.Map;
 
 /**
  * Noop impl for RemoteRoutingTableService.
@@ -32,11 +31,11 @@ public List<IndexRoutingTable> getIndicesRouting(RoutingTable routingTable) {
     }
 
     @Override
-    public DiffableUtils.MapDiff<String, IndexRoutingTable, Map<String, IndexRoutingTable>> getIndicesRoutingMapDiff(
+    public StringKeyDiffProvider<IndexRoutingTable> getIndicesRoutingMapDiff(
         RoutingTable before,
         RoutingTable after
     ) {
-        return new RoutingTableIncrementalDiff(before, after).getIndicesRouting();
+        return new RoutingTableIncrementalDiff(before, after);
     }
 
     @Override

server/src/main/java/org/opensearch/cluster/routing/remote/RemoteRoutingTableService.java

@@ -13,6 +13,7 @@
 import org.opensearch.cluster.DiffableUtils;
 import org.opensearch.cluster.routing.IndexRoutingTable;
 import org.opensearch.cluster.routing.RoutingTable;
+import org.opensearch.cluster.routing.StringKeyDiffProvider;
 import org.opensearch.common.lifecycle.LifecycleComponent;
 
 import org.opensearch.gateway.remote.ClusterMetadataManifest;
@@ -47,7 +48,7 @@ List<ClusterMetadataManifest.UploadedIndexMetadata> getUpdatedIndexRoutingTableM
         List<ClusterMetadataManifest.UploadedIndexMetadata> allIndicesRouting
     );
 
-    DiffableUtils.MapDiff<String, IndexRoutingTable, Map<String, IndexRoutingTable>> getIndicesRoutingMapDiff(
+    StringKeyDiffProvider<IndexRoutingTable> getIndicesRoutingMapDiff(
         RoutingTable before,
         RoutingTable after
     );

server/src/main/java/org/opensearch/gateway/remote/RemoteClusterStateService.java

@@ -27,7 +27,6 @@
 import org.opensearch.cluster.node.DiscoveryNodes.Builder;
 import org.opensearch.cluster.routing.IndexRoutingTable;
 import org.opensearch.cluster.routing.RoutingTable;
-import org.opensearch.cluster.routing.RoutingTableIncrementalDiff;
 import org.opensearch.cluster.routing.remote.RemoteRoutingTableService;
 import org.opensearch.cluster.routing.remote.RemoteRoutingTableServiceFactory;
 import org.opensearch.cluster.service.ClusterService;
@@ -343,7 +342,7 @@ public RemoteClusterStateManifestInfo writeIncrementalMetadata(
 
         final List<IndexRoutingTable> indicesRoutingToUpload = new ArrayList<>();
         final DiffableUtils.MapDiff<String, IndexRoutingTable, Map<String, IndexRoutingTable>> routingTableIncrementalDiff =
-            remoteRoutingTableService.getIndicesRoutingMapDiff(previousClusterState.getRoutingTable(), clusterState.getRoutingTable());
+            remoteRoutingTableService.getIndicesRoutingMapDiff(previousClusterState.getRoutingTable(), clusterState.getRoutingTable()).provideDiff();
 
         routingTableIncrementalDiff.getDiffs().forEach((k, v) -> indicesRoutingToUpload.add(clusterState.getRoutingTable().index(k)));
         routingTableIncrementalDiff.getUpserts().forEach((k, v) -> indicesRoutingToUpload.add(v));

server/src/main/java/org/opensearch/gateway/remote/routingtable/RemoteRoutingTableDiff.java

@@ -33,7 +33,7 @@ public class RemoteRoutingTableDiff extends AbstractRemoteWritableBlobEntity<Dif
 
     private final Diff<RoutingTable> routingTableDiff;
 
-    protected ChecksumWritableBlobStoreFormat<Diff<RoutingTable>> writeableBlobFormat;
+    private final ChecksumWritableBlobStoreFormat<Diff<RoutingTable>> writeableBlobFormat;
 
     private long term;
     private long version;
@@ -71,19 +71,6 @@ public RemoteRoutingTableDiff(
         this.writeableBlobFormat = writeableBlobFormat;
     }
 
-    /**
-     * Constructs a new RemoteRoutingTableDiff with the given differences.
-     *
-     * @param routingTableDiff a RoutingTableIncrementalDiff object containing the differences of {@link IndexRoutingTable}.
-     * @param clusterUUID the cluster UUID.
-     * @param compressor the compressor to be used.
-     */
-    public RemoteRoutingTableDiff(Diff<RoutingTable> routingTableDiff, ChecksumWritableBlobStoreFormat<Diff<RoutingTable>> writeableBlobFormat, String clusterUUID, Compressor compressor) {
-        super(clusterUUID, compressor);
-        this.routingTableDiff = routingTableDiff;
-        this.writeableBlobFormat = writeableBlobFormat;
-    }
-
     /**
      * Constructs a new RemoteIndexRoutingTableDiff with the given blob name, cluster UUID, and compressor.
      *
@@ -94,6 +81,7 @@ public RemoteRoutingTableDiff(Diff<RoutingTable> routingTableDiff, ChecksumWrita
     public RemoteRoutingTableDiff(String blobName, String clusterUUID, Compressor compressor) {
         super(clusterUUID, compressor);
         this.routingTableDiff = null;
+        this.writeableBlobFormat = null;
         this.blobName = blobName;
     }
 

server/src/test/java/org/opensearch/gateway/remote/model/ClusterStateDiffManifestTests.java

@@ -165,7 +165,7 @@ private ClusterStateDiffManifest verifyRoutingTableDiffManifest(ClusterState pre
         // Create initial and updated IndexRoutingTable maps
         DiffableUtils.MapDiff<String, IndexRoutingTable, Map<String, IndexRoutingTable>> routingTableIncrementalDiff = new RoutingTableIncrementalDiff(
             previousState.getRoutingTable(),
-            currentState.getRoutingTable()).getIndicesRouting();
+            currentState.getRoutingTable()).provideDiff();
         ClusterStateDiffManifest manifest = new ClusterStateDiffManifest(
             currentState,
             previousState,