Add `count` value to rest output of `geo_centroid` (#24387)

Currently we don't write the count value to the geo_centroid aggregation rest response,
but it is provided via the java api and the count() method in the GeoCentroid interface. 
We should add this parameter to the rest output and also provide it via the getProperty()
method.

core/src/main/java/org/elasticsearch/search/aggregations/metrics/geocentroid/InternalGeoCentroid.java

@@ -20,6 +20,7 @@
 package org.elasticsearch.search.aggregations.metrics.geocentroid;
 
 import org.apache.lucene.geo.GeoEncodingUtils;
+import org.elasticsearch.common.ParseField;
 import org.elasticsearch.common.geo.GeoPoint;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
@@ -36,8 +37,8 @@ import java.util.Objects;
  * Serialization and merge logic for {@link GeoCentroidAggregator}.
  */
 public class InternalGeoCentroid extends InternalAggregation implements GeoCentroid {
-    protected final GeoPoint centroid;
-    protected final long count;
+    private final GeoPoint centroid;
+    private final long count;
 
     public static long encodeLatLon(double lat, double lon) {
         return (Integer.toUnsignedLong(GeoEncodingUtils.encodeLatitude(lat)) << 32) | Integer.toUnsignedLong(GeoEncodingUtils.encodeLongitude(lon));
@@ -136,6 +137,8 @@ public class InternalGeoCentroid extends InternalAggregation implements GeoCentr
                     return centroid.lat();
                 case "lon":
                     return centroid.lon();
+                case "count":
+                    return count;
                 default:
                     throw new IllegalArgumentException("Found unknown path element [" + coordinate + "] in [" + getName() + "]");
             }
@@ -145,14 +148,27 @@ public class InternalGeoCentroid extends InternalAggregation implements GeoCentr
     }
 
     static class Fields {
-        static final String CENTROID = "location";
+        static final ParseField CENTROID = new ParseField("location");
+        static final ParseField CENTROID_LAT = new ParseField("lat");
+        static final ParseField CENTROID_LON = new ParseField("lon");
+        static final ParseField COUNT = new ParseField("count");
     }
 
     @Override
     public XContentBuilder doXContentBody(XContentBuilder builder, Params params) throws IOException {
+        return renderXContent(builder, params, centroid, count);
+    }
+
+    static XContentBuilder renderXContent(XContentBuilder builder, Params params, GeoPoint centroid, long count) throws IOException {
         if (centroid != null) {
-            builder.startObject(Fields.CENTROID).field("lat", centroid.lat()).field("lon", centroid.lon()).endObject();
+            builder.startObject(Fields.CENTROID.getPreferredName());
+            {
+                builder.field(Fields.CENTROID_LAT.getPreferredName(), centroid.lat());
+                builder.field(Fields.CENTROID_LON.getPreferredName(), centroid.lon());
+            }
+            builder.endObject();
         }
+        builder.field(Fields.COUNT.getPreferredName(), count);
         return builder;
     }
 

core/src/test/java/org/elasticsearch/search/aggregations/metrics/GeoCentroidIT.java

@@ -59,6 +59,7 @@ public class GeoCentroidIT extends AbstractGeoTestCase {
         assertThat(geoCentroid.getName(), equalTo(aggName));
         GeoPoint centroid = geoCentroid.centroid();
         assertThat(centroid, equalTo(null));
+        assertEquals(0, geoCentroid.count());
     }
 
     public void testUnmapped() throws Exception {
@@ -72,6 +73,7 @@ public class GeoCentroidIT extends AbstractGeoTestCase {
         assertThat(geoCentroid.getName(), equalTo(aggName));
         GeoPoint centroid = geoCentroid.centroid();
         assertThat(centroid, equalTo(null));
+        assertEquals(0, geoCentroid.count());
     }
 
     public void testPartiallyUnmapped() throws Exception {
@@ -86,6 +88,7 @@ public class GeoCentroidIT extends AbstractGeoTestCase {
         GeoPoint centroid = geoCentroid.centroid();
         assertThat(centroid.lat(), closeTo(singleCentroid.lat(), GEOHASH_TOLERANCE));
         assertThat(centroid.lon(), closeTo(singleCentroid.lon(), GEOHASH_TOLERANCE));
+        assertEquals(numDocs, geoCentroid.count());
     }
 
     public void testSingleValuedField() throws Exception {
@@ -101,6 +104,7 @@ public class GeoCentroidIT extends AbstractGeoTestCase {
         GeoPoint centroid = geoCentroid.centroid();
         assertThat(centroid.lat(), closeTo(singleCentroid.lat(), GEOHASH_TOLERANCE));
         assertThat(centroid.lon(), closeTo(singleCentroid.lon(), GEOHASH_TOLERANCE));
+        assertEquals(numDocs, geoCentroid.count());
     }
 
     public void testSingleValueFieldGetProperty() throws Exception {
@@ -130,6 +134,7 @@ public class GeoCentroidIT extends AbstractGeoTestCase {
                 closeTo(singleCentroid.lon(), GEOHASH_TOLERANCE));
         assertThat((double) ((InternalAggregation)global).getProperty(aggName + ".lat"), closeTo(singleCentroid.lat(), GEOHASH_TOLERANCE));
         assertThat((double) ((InternalAggregation)global).getProperty(aggName + ".lon"), closeTo(singleCentroid.lon(), GEOHASH_TOLERANCE));
+        assertEquals(numDocs, (long) ((InternalAggregation) global).getProperty(aggName + ".count"));
     }
 
     public void testMultiValuedField() throws Exception {
@@ -145,6 +150,7 @@ public class GeoCentroidIT extends AbstractGeoTestCase {
         GeoPoint centroid = geoCentroid.centroid();
         assertThat(centroid.lat(), closeTo(multiCentroid.lat(), GEOHASH_TOLERANCE));
         assertThat(centroid.lon(), closeTo(multiCentroid.lon(), GEOHASH_TOLERANCE));
+        assertEquals(2 * numDocs, geoCentroid.count());
     }
 
     public void testSingleValueFieldAsSubAggToGeohashGrid() throws Exception {

core/src/test/java/org/elasticsearch/search/aggregations/metrics/geocentroid/InternalGeoCentroidTests.java

@@ -42,8 +42,11 @@ public class InternalGeoCentroidTests extends InternalAggregationTestCase<Intern
         centroid.resetLon(GeoEncodingUtils.decodeLongitude(encodedLon));
         int encodedLat = GeoEncodingUtils.encodeLatitude(centroid.lat());
         centroid.resetLat(GeoEncodingUtils.decodeLatitude(encodedLat));
-
-        return new InternalGeoCentroid("_name", centroid, 1, Collections.emptyList(), Collections.emptyMap());
+        long count = randomIntBetween(0, 1000);
+        if (count == 0) {
+            centroid = null;
+        }
+        return new InternalGeoCentroid("_name", centroid, count, Collections.emptyList(), Collections.emptyMap());
     }
 
     @Override
@@ -53,14 +56,18 @@ public class InternalGeoCentroidTests extends InternalAggregationTestCase<Intern
 
     @Override
     protected void assertReduced(InternalGeoCentroid reduced, List<InternalGeoCentroid> inputs) {
-        GeoPoint expected = new GeoPoint(0, 0);
-        int i = 0;
+        double lonSum = 0;
+        double latSum = 0;
+        int totalCount = 0;
         for (InternalGeoCentroid input : inputs) {
-            expected.reset(expected.lat() + (input.centroid().lat() - expected.lat()) / (i+1),
-                    expected.lon() + (input.centroid().lon() - expected.lon()) / (i+1));
-            i++;
+            if (input.count() > 0) {
+                lonSum += (input.count() * input.centroid().getLon());
+                latSum += (input.count() * input.centroid().getLat());
+            }
+            totalCount += input.count();
         }
-        assertEquals(expected.getLat(), reduced.centroid().getLat(), 1E-5D);
-        assertEquals(expected.getLon(), reduced.centroid().getLon(), 1E-5D);
+        assertEquals(latSum/totalCount, reduced.centroid().getLat(), 1E-5D);
+        assertEquals(lonSum/totalCount, reduced.centroid().getLon(), 1E-5D);
+        assertEquals(totalCount, reduced.count());
     }
 }

docs/reference/aggregations/metrics/geocentroid-aggregation.asciidoc

@@ -62,7 +62,8 @@ The response for the above aggregation:
             "location": {
                 "lat": 51.00982963107526,
                 "lon": 3.9662130922079086
-            }
+            },
+            "count": 6
         }
     }
 }
@@ -114,7 +115,8 @@ The response for the above aggregation:
                       "location": {
                          "lat": 52.371655656024814,
                          "lon": 4.909563297405839
-                      }
+                      },
+                      "count": 3
                    }
                },
                {
@@ -124,7 +126,8 @@ The response for the above aggregation:
                       "location": {
                          "lat": 48.86055548675358,
                          "lon": 2.3316944623366
-                      }
+                      },
+                      "count": 2
                    }
                 },
                 {
@@ -134,7 +137,8 @@ The response for the above aggregation:
                        "location": {
                           "lat": 51.22289997059852,
                           "lon": 4.40519998781383
-                       }
+                       },
+                       "count": 1
                     }
                  }
             ]