Fixed issues in reduce

Signed-off-by: Vinay Krishna Pudyodu <vinkrish.neo@gmail.com>

Author: vinaykpud

server/src/main/java/org/opensearch/search/aggregations/bucket/terms/InternalTerms.java

@@ -459,9 +459,9 @@ For backward compatibility, we disable the merge sort and use ({@link InternalTe
         final B[] list;
         if (reduceContext.isFinalReduce() || reduceContext.isSliceLevel()) {
             final int size = Math.min(localBucketCountThresholds.getRequiredSize(), reducedBuckets.size());
-
-            Comparator<MultiBucketsAggregation.Bucket> cmp = order.comparator();
-            int countOfBucketsAboveMinCount = 0;
+            final Comparator<MultiBucketsAggregation.Bucket> cmp = order.comparator();
+            int validBucketCount = 0;
+            // Process buckets and update doc count errors and count valid buckets
             for (B bucket : reducedBuckets) {
                 if (sumDocCountError == -1) {
                     bucket.setDocCountError(-1);
@@ -473,36 +473,38 @@ For backward compatibility, we disable the merge sort and use ({@link InternalTe
                 if (bucket.getDocCount() < localBucketCountThresholds.getMinDocCount()) {
                     reduceContext.consumeBucketsAndMaybeBreak(-countInnerBucket(bucket));
                 } else {
-                    countOfBucketsAboveMinCount++;
+                    validBucketCount++;
                 }
             }
-
-            B[] reducedBucketsFinal = createBucketsArray(countOfBucketsAboveMinCount);
-            int reducedBucketsFinalCount = 0;
+            // Create array and populate with valid buckets
+            B[] validBuckets = createBucketsArray(validBucketCount);
+            int arrayIndex = 0;
             for (B bucket : reducedBuckets) {
                 if (bucket.getDocCount() >= localBucketCountThresholds.getMinDocCount()) {
-                    reducedBucketsFinal[reducedBucketsFinalCount++] = bucket;
+                    validBuckets[arrayIndex++] = bucket;
                 }
             }
-
-            if (size < reducedBucketsFinalCount) {
-                ArrayUtil.select(reducedBucketsFinal, 0, reducedBucketsFinalCount, size, cmp);
+            // Select top buckets if needed
+            if (size < validBuckets.length) {
+                ArrayUtil.select(validBuckets, 0, validBuckets.length, size, cmp);
             }
-
-            int selectSize = 0;
-            for (B bucket : reducedBucketsFinal) {
-                B removed = ((selectSize == size) ? bucket : null);
-                if (removed != null) {
-                    otherDocCount += removed.getDocCount();
-                    reduceContext.consumeBucketsAndMaybeBreak(-countInnerBucket(removed));
-                } else {
-                    selectSize++;
+            // Process selected buckets and calculate otherDocCount
+            int finalSize = Math.min(size, validBuckets.length);
+            for (int i = 0; i < validBuckets.length; i++) {
+                B bucket = validBuckets[i];
+                if (i < finalSize) {
                     reduceContext.consumeBucketsAndMaybeBreak(1);
+                } else {
+                    otherDocCount += bucket.getDocCount();
+                    reduceContext.consumeBucketsAndMaybeBreak(-countInnerBucket(bucket));
                 }
             }
-
-            list = createBucketsArray(selectSize);
-            if (selectSize >= 0) System.arraycopy(reducedBucketsFinal, 0, list, 0, selectSize);
+            if (finalSize != validBuckets.length) {
+                list = createBucketsArray(finalSize);
+                System.arraycopy(validBuckets, 0, list, 0, finalSize);
+            } else {
+                list = validBuckets;
+            }
             Arrays.sort(list, cmp);
         } else {
             // we can prune the list on partial reduce if the aggregation is ordered by key