From 8e5680998271781fe04d9f3c87ca5e09fd2dae86 Mon Sep 17 00:00:00 2001
From: Ridhwaan Anayetullah <ridhwaan.any@gmail.com>
Date: Mon, 14 Jun 2021 12:38:47 +0000
Subject: SERVER-57332 Create skeleton InternalDocumentSourceDensify

---
 src/mongo/db/pipeline/document_source_densify.cpp |  4 ++
 src/mongo/db/pipeline/document_source_densify.h   | 45 ++++++++++++++++++++++-
 2 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/src/mongo/db/pipeline/document_source_densify.cpp b/src/mongo/db/pipeline/document_source_densify.cpp
index 7f537a6a9b6..c7d8b122c31 100644
--- a/src/mongo/db/pipeline/document_source_densify.cpp
+++ b/src/mongo/db/pipeline/document_source_densify.cpp
@@ -141,4 +141,8 @@ bool DocumentSourceInternalDensify::DocGenerator::done() const {
     return _state == GeneratorState::kDone;
 }
 
+DocumentSource::GetNextResult DocumentSourceInternalDensify::doGetNext() {
+    return pSource->getNext();
+}
+
 }  // namespace mongo
diff --git a/src/mongo/db/pipeline/document_source_densify.h b/src/mongo/db/pipeline/document_source_densify.h
index b25c482f9fe..ffc921d4714 100644
--- a/src/mongo/db/pipeline/document_source_densify.h
+++ b/src/mongo/db/pipeline/document_source_densify.h
@@ -31,6 +31,7 @@
 
 #include "mongo/db/exec/document_value/document.h"
 #include "mongo/db/exec/document_value/value.h"
+#include "mongo/db/pipeline/document_source.h"
 #include "mongo/db/pipeline/field_path.h"
 #include "mongo/db/query/datetime/date_time_support.h"
 #include "mongo/util/time_support.h"
@@ -42,14 +43,17 @@ namespace document_source_densify {
 }
 
 // TODO SERVER-57332 This should inherit from DocumentSource.
-class DocumentSourceInternalDensify {
+class DocumentSourceInternalDensify final : public DocumentSource {
 public:
+    static constexpr StringData kStageName = "$_internalDensify"_sd;
+
     using DensifyValueType = stdx::variant<double, Date_t>;
     struct StepSpec {
         double step;
         boost::optional<TimeUnit> unit;
         boost::optional<TimeZone> tz;
     };
+
     class DocGenerator {
     public:
         DocGenerator(DensifyValueType min,
@@ -85,5 +89,42 @@ public:
 
         GeneratorState _state = GeneratorState::kGeneratingDocuments;
     };
+
+    static boost::intrusive_ptr<DocumentSourceInternalDensify> create(const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
+
+    static boost::intrusive_ptr<DocumentSource> createFromBson(
+        BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
+
+    StageConstraints constraints(Pipeline::SplitState pipeState) const final {
+        return {StreamType::kStreaming,
+                PositionRequirement::kNone,
+                HostTypeRequirement::kNone,
+                DiskUseRequirement::kNoDiskUse,
+                FacetRequirement::kAllowed,
+                TransactionRequirement::kAllowed,
+                LookupRequirement::kAllowed,
+                UnionRequirement::kAllowed};
+    }
+
+    const char* getSourceName() const final {
+        return kStageName.rawData();
+    }
+    Pipeline::SourceContainer::iterator doOptimizeAt(Pipeline::SourceContainer::iterator itr,
+                                                     Pipeline::SourceContainer* container) final;
+    Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
+
+    DepsTracker::State getDependencies(DepsTracker* deps) const final {
+        return DepsTracker::State::SEE_NEXT;  // This doesn't affect needed fields
+    }
+
+    boost::optional<DistributedPlanLogic> distributedPlanLogic() final {
+        // Running this stage on the shards is an optimization, but is not strictly necessary in
+        // order to produce correct pipeline output.
+        // {shardsStage, mergingStage, sortPattern}
+        return DistributedPlanLogic{nullptr, this, boost::none};
+    }
+
+    DocumentSourceInternalDensify(const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
+    GetNextResult doGetNext() final;
 };
-}  // namespace mongo
+};  
-- 
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