Add kcore in compute facade

Author: IoannisPanagiotas

algo/src/main/java/org/neo4j/gds/kcore/KCoreDecompositionResult.java

@@ -21,4 +21,7 @@
 
 import org.neo4j.gds.collections.ha.HugeIntArray;
 
-public record KCoreDecompositionResult(HugeIntArray coreValues, int degeneracy){}
+public record KCoreDecompositionResult(HugeIntArray coreValues, int degeneracy){
+
+public static KCoreDecompositionResult EMPTY = new KCoreDecompositionResult(HugeIntArray.newArray(0), 0);
+}

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

@@ -40,6 +40,9 @@
 import org.neo4j.gds.k1coloring.K1Coloring;
 import org.neo4j.gds.k1coloring.K1ColoringParameters;
 import org.neo4j.gds.k1coloring.K1ColoringResult;
+import org.neo4j.gds.kcore.KCoreDecomposition;
+import org.neo4j.gds.kcore.KCoreDecompositionParameters;
+import org.neo4j.gds.kcore.KCoreDecompositionResult;
 import org.neo4j.gds.result.TimedAlgorithmResult;
 import org.neo4j.gds.termination.TerminationFlag;
 
@@ -231,4 +234,35 @@ CompletableFuture<TimedAlgorithmResult<K1ColoringResult>> k1Coloring(
             jobId
         );
     }
+
+    CompletableFuture<TimedAlgorithmResult<KCoreDecompositionResult>> kCore(
+        Graph graph,
+        KCoreDecompositionParameters parameters,
+        JobId jobId,
+        boolean logProgress
+    ) {
+
+        if (graph.isEmpty()) {
+            return CompletableFuture.completedFuture(TimedAlgorithmResult.empty(KCoreDecompositionResult.EMPTY));
+        }
+
+        var progressTracker = progressTrackerFactory.create(
+            tasks.kCore(graph),
+            jobId,
+            parameters.concurrency(),
+            logProgress
+        );
+
+        var algorithm = new KCoreDecomposition(
+            graph,
+            parameters.concurrency(),
+            progressTracker,
+            terminationFlag
+        );
+
+        return algorithmCaller.run(
+            algorithm::compute,
+            jobId
+        );
+    }
 }

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

@@ -38,6 +38,8 @@
 import org.neo4j.gds.hdbscan.Labels;
 import org.neo4j.gds.k1coloring.K1ColoringParameters;
 import org.neo4j.gds.k1coloring.K1ColoringResult;
+import org.neo4j.gds.kcore.KCoreDecompositionParameters;
+import org.neo4j.gds.kcore.KCoreDecompositionResult;
 import org.neo4j.gds.termination.TerminationFlag;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -152,4 +154,21 @@ void k1Coloring(){
         verifyNoInteractions(algorithmCallerMock);
     }
 
+    @Test
+    void kCore(){
+
+        var future = facade.kCore(
+            graph,
+            mock(KCoreDecompositionParameters.class),
+            jobIdMock,
+            false
+        );
+
+        var results = future.join();
+
+        assertThat(results.result()).isEqualTo(KCoreDecompositionResult.EMPTY);
+        verifyNoInteractions(progressTrackerFactoryMock);
+        verifyNoInteractions(algorithmCallerMock);
+    }
+
 }

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

@@ -41,6 +41,7 @@
 import org.neo4j.gds.extension.TestGraph;
 import org.neo4j.gds.hdbscan.HDBScanParameters;
 import org.neo4j.gds.k1coloring.K1ColoringParameters;
+import org.neo4j.gds.kcore.KCoreDecompositionParameters;
 import org.neo4j.gds.logging.Log;
 import org.neo4j.gds.termination.TerminationFlag;
 
@@ -200,4 +201,22 @@ void k1Coloring(){
         assertThat(results.result().ranIterations()).isGreaterThan(0);
         assertThat(results.computeMillis()).isNotNegative();
     }
+
+    @Test
+    void kCore(){
+        var future = facade.kCore(
+            graph,
+            new KCoreDecompositionParameters(
+                new Concurrency(4)
+            ),
+            jobIdMock,
+            false
+        );
+
+        var results = future.join();
+
+        assertThat(results.result().degeneracy()).isGreaterThan(0);
+        assertThat(results.computeMillis()).isNotNegative();
+    }
+
 }