Add modularity in compute facade

Author: IoannisPanagiotas

algo/src/main/java/org/neo4j/gds/modularity/ModularityResult.java

@@ -27,4 +27,13 @@ public record ModularityResult(
         double totalModularity,
         long communityCount,
         HugeObjectArray<CommunityModularity> modularityScores
-    ) { }
+    ) {
+
+    public static  ModularityResult EMPTY  = new ModularityResult(
+        0,
+        0,
+        0,
+        0,
+        HugeObjectArray.newArray(CommunityModularity.class,0)
+    );
+}

algorithms-compute-facade/src/main/java/org/neo4j/gds/community/CommunityComputeFacade.java

@@ -57,6 +57,9 @@
 import org.neo4j.gds.louvain.Louvain;
 import org.neo4j.gds.louvain.LouvainParameters;
 import org.neo4j.gds.louvain.LouvainResult;
+import org.neo4j.gds.modularity.ModularityCalculator;
+import org.neo4j.gds.modularity.ModularityParameters;
+import org.neo4j.gds.modularity.ModularityResult;
 import org.neo4j.gds.result.TimedAlgorithmResult;
 import org.neo4j.gds.termination.TerminationFlag;
 import org.neo4j.gds.triangle.LocalClusteringCoefficient;
@@ -448,4 +451,26 @@ CompletableFuture<TimedAlgorithmResult<LouvainResult>> louvain(
         );
     }
 
+    CompletableFuture<TimedAlgorithmResult<ModularityResult>> modularity(
+        Graph graph,
+        ModularityParameters parameters,
+        JobId jobId
+    ) {
+
+        if (graph.isEmpty()) {
+            return CompletableFuture.completedFuture(TimedAlgorithmResult.empty(ModularityResult.EMPTY));
+        }
+
+        var algorithm = ModularityCalculator.create(
+            graph,
+            graph.nodeProperties(parameters.communityProperty())::longValue,
+            parameters.concurrency()
+        );
+
+        return algorithmCaller.run(
+            algorithm::compute,
+            jobId
+        );
+    }
+
 }

algorithms-compute-facade/src/test/java/org/neo4j/gds/community/CommunityComputeFacadeEmptyGraphTest.java

@@ -47,6 +47,8 @@
 import org.neo4j.gds.leiden.LeidenResult;
 import org.neo4j.gds.louvain.LouvainParameters;
 import org.neo4j.gds.louvain.LouvainResult;
+import org.neo4j.gds.modularity.ModularityParameters;
+import org.neo4j.gds.modularity.ModularityResult;
 import org.neo4j.gds.termination.TerminationFlag;
 import org.neo4j.gds.triangle.LocalClusteringCoefficientParameters;
 import org.neo4j.gds.triangle.LocalClusteringCoefficientResult;
@@ -268,4 +270,20 @@ void louvain(){
         verifyNoInteractions(progressTrackerFactoryMock);
         verifyNoInteractions(algorithmCallerMock);
     }
+
+    @Test
+    void modularity(){
+
+        var future = facade.modularity(
+            graph,
+            mock(ModularityParameters.class),
+            jobIdMock
+        );
+
+        var results = future.join();
+
+        assertThat(results.result()).isEqualTo(ModularityResult.EMPTY);
+        verifyNoInteractions(progressTrackerFactoryMock);
+        verifyNoInteractions(algorithmCallerMock);
+    }
 }

algorithms-compute-facade/src/test/java/org/neo4j/gds/community/CommunityComputeFacadeTest.java

@@ -48,6 +48,7 @@
 import org.neo4j.gds.leiden.LeidenParameters;
 import org.neo4j.gds.logging.Log;
 import org.neo4j.gds.louvain.LouvainParameters;
+import org.neo4j.gds.modularity.ModularityParameters;
 import org.neo4j.gds.termination.TerminationFlag;
 import org.neo4j.gds.triangle.LocalClusteringCoefficientParameters;
 
@@ -336,4 +337,21 @@ void louvain(){
         assertThat(results.computeMillis()).isNotNegative();
     }
 
+    @Test
+    void modularity(){
+        var future = facade.modularity(
+            graph,
+            new ModularityParameters(
+               "prop",
+                new Concurrency(4)
+            ),
+            jobIdMock
+        );
+
+        var results = future.join();
+
+        assertThat(results.result().nodeCount()).isEqualTo(3);
+        assertThat(results.computeMillis()).isNotNegative();
+    }
+
 }