text: /**
   *    Copyright (C) 2013-2014 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 "mongo/db/catalog/collection.h"
  #include "mongo/db/exec/plan_stage.h"
  #include "mongo/db/query/canonical_query.h"
  #include "mongo/db/record_id.h"
  
  namespace mongo {
  
      /**
       * A standalone stage implementing the fast path for key-value retrievals
       * via the _id index.
       */
      class IDHackStage : public PlanStage {
      public:
          /** Takes ownership of all the arguments -collection. */
          IDHackStage(OperationContext* txn, const Collection* collection,
                      CanonicalQuery* query, WorkingSet* ws);
  
          IDHackStage(OperationContext* txn, Collection* collection,
                      const BSONObj& key, WorkingSet* ws);
  
          virtual ~IDHackStage();
  
          virtual bool isEOF();
          virtual StageState work(WorkingSetID* out);
  
          virtual void saveState();
          virtual void restoreState(OperationContext* opCtx);
          virtual void invalidate(OperationContext* txn, const RecordId& dl, InvalidationType type);
  
          /**
           * ID Hack has a very strict criteria for the queries it supports.
           */
          static bool supportsQuery(const CanonicalQuery& query);
  
          virtual std::vector<PlanStage*> getChildren() const;
  
          virtual StageType stageType() const { return STAGE_IDHACK; }
  
          PlanStageStats* getStats();
  
          virtual const CommonStats* getCommonStats() const;
  
          virtual const SpecificStats* getSpecificStats() const;
  
          static const char* kStageType;
  
      private:
          /**
           * Marks this stage as done, optionally adds key metadata, and returns PlanStage::ADVANCED.
           *
           * Called whenever we have a WSM containing the matching obj.
           */
          StageState advance(WorkingSetID id, WorkingSetMember* member, WorkingSetID* out);
  
          // transactional context for read locks. Not owned by us
          OperationContext* _txn;
  
          // Not owned here.
          const Collection* _collection;
  
          // The WorkingSet we annotate with results.  Not owned by us.
          WorkingSet* _workingSet;
  
          // The value to match against the _id field.
          BSONObj _key;
  
          // Have we returned our one document?
          bool _done;
  
          // Do we need to add index key metadata for $returnKey?
          bool _addKeyMetadata;
  
          // If we want to return a RecordId and it points to something that's not in memory,
          // we return a "please page this in" result. We add a RecordFetcher given back to us by the
          // storage engine to the WSM. The RecordFetcher is used by the PlanExecutor when it handles
          // the fetch request.
          WorkingSetID _idBeingPagedIn;
  
          CommonStats _commonStats;
          IDHackStats _specificStats;
      };
  
  }  // namespace mongo
  