Query: Adds hybrid search query pipeline stage

Microsoft.Azure.Cosmos/src/Query/Core/Pipeline/Aggregate/Aggregators/SingleGroupAggregator.cs

@@ -341,7 +341,8 @@ public static TryCatch<AggregateValue> TryCreate(
                             tryCreateAggregator = AverageAggregator.TryCreate(continuationToken);
                             break;
 
-                        case AggregateOperator.Count:
+                        case AggregateOperator.Count:
+                        case AggregateOperator.CountIf:
                             tryCreateAggregator = CountAggregator.TryCreate(continuationToken);
                             break;
 

Microsoft.Azure.Cosmos/src/Query/Core/Pipeline/CrossPartition/HybridSearch/FullTextStatistics.cs

@@ -0,0 +1,64 @@
+// ------------------------------------------------------------
+// Copyright (c) Microsoft Corporation.  All rights reserved.
+// ------------------------------------------------------------
+
+namespace Microsoft.Azure.Cosmos.Query.Core.Pipeline.CrossPartition.HybridSearch
+{
+    using System;
+    using System.Collections.Generic;
+    using Microsoft.Azure.Cosmos.CosmosElements;
+
+    internal sealed class FullTextStatistics
+    {
+        private readonly long[] hitCounts;
+
+        public long TotalWordCount { get; }
+
+        public ReadOnlyMemory<long> HitCounts => this.hitCounts;
+
+        public FullTextStatistics(long totalWordCount, long[] hitCounts)
+        {
+            this.TotalWordCount = totalWordCount;
+            this.hitCounts = hitCounts;
+        }
+
+        public FullTextStatistics(CosmosObject cosmosObject)
+        {
+            if (cosmosObject == null)
+            {
+                throw new System.ArgumentNullException($"{nameof(cosmosObject)} must not be null.");
+            }
+
+            if (!cosmosObject.TryGetValue(FieldNames.TotalWordCount, out CosmosNumber totalWordCount))
+            {
+                throw new System.ArgumentException($"{FieldNames.TotalWordCount} must exist and be a number");
+            }
+
+            if (!cosmosObject.TryGetValue(FieldNames.HitCounts, out CosmosArray hitCountsArray))
+            {
+                throw new System.ArgumentException($"{FieldNames.HitCounts} must exist and be an array");
+            }
+
+            long[] hitCounts = new long[hitCountsArray.Count];
+            for (int index = 0; index < hitCountsArray.Count; ++index)
+            {
+                if (!(hitCountsArray[index] is CosmosNumber cosmosNumber))
+                {
+                    throw new System.ArgumentException($"{FieldNames.HitCounts} must be an array of numbers");
+                }
+
+                hitCounts[index] = Number64.ToLong(cosmosNumber.Value);
+            }
+
+            this.TotalWordCount = Number64.ToLong(totalWordCount.Value);
+            this.hitCounts = hitCounts;
+        }
+
+        private static class FieldNames
+        {
+            public const string TotalWordCount = "totalWordCount";
+
+            public const string HitCounts = "hitCounts";
+        }
+    }
+}

Microsoft.Azure.Cosmos/src/Query/Core/Pipeline/CrossPartition/HybridSearch/GlobalFullTextSearchStatistics.cs

@@ -0,0 +1,67 @@
+// ------------------------------------------------------------
+// Copyright (c) Microsoft Corporation.  All rights reserved.
+// ------------------------------------------------------------
+
+namespace Microsoft.Azure.Cosmos.Query.Core.Pipeline.CrossPartition.HybridSearch
+{
+    using System.Collections.Generic;
+    using Microsoft.Azure.Cosmos.CosmosElements;
+
+    internal sealed class GlobalFullTextSearchStatistics
+    {
+        public long DocumentCount { get; }
+
+        public IReadOnlyList<FullTextStatistics> FullTextStatistics { get; }
+
+        public GlobalFullTextSearchStatistics(long documentCount, IReadOnlyList<FullTextStatistics> fullTextStatistics)
+        {
+            this.DocumentCount = documentCount;
+            this.FullTextStatistics = fullTextStatistics ?? throw new System.ArgumentNullException($"{nameof(fullTextStatistics)} must not be null.");
+        }
+
+        public GlobalFullTextSearchStatistics(CosmosElement cosmosElement)
+        {
+            if (cosmosElement == null)
+            {
+                throw new System.ArgumentNullException($"{nameof(cosmosElement)} must not be null.");
+            }
+
+            if (!(cosmosElement is CosmosObject cosmosObject))
+            {
+                throw new System.ArgumentException($"{nameof(cosmosElement)} must be an object.");
+            }
+
+            if (!cosmosObject.TryGetValue(FieldNames.DocumentCount, out CosmosNumber cosmosNumber))
+            {
+                throw new System.ArgumentException($"{FieldNames.DocumentCount} must exist and be a number");
+            }
+
+            if (!cosmosObject.TryGetValue(FieldNames.Statistics, out CosmosArray statisticsArray))
+            {
+                throw new System.ArgumentException($"{FieldNames.Statistics} must exist and be an array");
+            }
+
+            List<FullTextStatistics> fullTextStatisticsList = new List<FullTextStatistics>(statisticsArray.Count);
+            foreach (CosmosElement statisticsElement in statisticsArray)
+            {
+                if (!(statisticsElement is CosmosObject))
+                {
+                    throw new System.ArgumentException($"{FieldNames.Statistics} must be an array of objects");
+                }
+
+                FullTextStatistics fullTextStatistics = new FullTextStatistics(statisticsElement as CosmosObject);
+                fullTextStatisticsList.Add(fullTextStatistics);
+            }
+
+            this.DocumentCount = Number64.ToLong(cosmosNumber.Value);
+            this.FullTextStatistics = fullTextStatisticsList;
+        }
+
+        private static class FieldNames
+        {
+            public const string DocumentCount = "documentCount";
+
+            public const string Statistics = "fullTextStatistics";
+        }
+    }
+}