text: /**
   *    Copyright (C) 2014 MongoDB Inc.
   *
   *    This program is free software: you can redistribute it and/or  modify
   *    it under the terms of the GNU Affero General Public License, version 3,
   *    as published by the Free Software Foundation.
   *
   *    This program is distributed in the hope that it will be useful,
   *    but WITHOUT ANY WARRANTY; without even the implied warranty of
   *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   *    GNU Affero General Public License for more details.
   *
   *    You should have received a copy of the GNU Affero General Public License
   *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
   *
   *    As a special exception, the copyright holders give permission to link the
   *    code of portions of this program with the OpenSSL library under certain
   *    conditions as described in each individual source file and distribute
   *    linked combinations including the program with the OpenSSL library. You
   *    must comply with the GNU Affero General Public License in all respects for
   *    all of the code used other than as permitted herein. If you modify file(s)
   *    with this exception, you may extend this exception to your version of the
   *    file(s), but you are not obligated to do so. If you do not wish to do so,
   *    delete this exception statement from your version. If you delete this
   *    exception statement from all source files in the program, then also delete
   *    it in the license file.
   */
  
  #pragma once
  
  #include <boost/optional/optional.hpp>
  #include <boost/intrusive_ptr.hpp>
  
  #include "mongol/db/catalog/collection.h"
  #include "mongol/db/exec/plan_stage.h"
  #include "mongol/db/exec/plan_stats.h"
  #include "mongol/db/pipeline/pipeline.h"
  #include "mongol/db/record_id.h"
  
  namespace mongol {
  
  /**
   * Stage for pulling results out from an aggregation pipeline.
   */
  class PipelineProxyStage final : public PlanStage {
  public:
      PipelineProxyStage(OperationContext* opCtx,
                         boost::intrusive_ptr<Pipeline> pipeline,
                         const std::shared_ptr<PlanExecutor>& child,
                         WorkingSet* ws);
  
      PlanStage::StageState work(WorkingSetID* out) final;
  
      bool isEOF() final;
  
      void doInvalidate(OperationContext* txn, const RecordId& dl, InvalidationType type) final;
  
      //
      // Manage our OperationContext.
      //
      void doDetachFromOperationContext() final;
      void doReattachToOperationContext() final;
  
      /**
       * Return a shared pointer to the PlanExecutor that feeds the pipeline. The returned
       * pointer may be NULL.
       */
      std::shared_ptr<PlanExecutor> getChildExecutor();
  
      // Returns empty PlanStageStats object
      std::unique_ptr<PlanStageStats> getStats() final;
  
  
      // Not used.
      SpecificStats* getSpecificStats() const final {
          return NULL;
      }
  
      // Not used.
      StageType stageType() const final {
          return STAGE_PIPELINE_PROXY;
      }
  
      static const char* kStageType;
  
  private:
      boost::optional<BSONObj> getNextBson();
  
      // Things in the _stash should be returned before pulling items from _pipeline.
      const boost::intrusive_ptr<Pipeline> _pipeline;
      std::vector<BSONObj> _stash;
      const bool _includeMetaData;
      std::weak_ptr<PlanExecutor> _childExec;
  
      // Not owned by us.
      WorkingSet* _ws;
  };
  
  }  // namespace mongol
  