/**
 *    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 "mongo/db/diskloc.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/exec/plan_stage.h"
#include "mongo/db/matcher/expression.h"

namespace mongo {

    /**
     * KeepMutationsStage passes all of its child's data through until the child is EOF.
     * It then returns all flagged elements in the WorkingSet that pass the stage's filter.
     *
     * This stage is used to merge results that are invalidated mid-query back into the query
     * results when possible.  The query planner is responsible for determining when it's valid to
     * merge these results.
     */
    class KeepMutationsStage : public PlanStage {
    public:
        KeepMutationsStage(const MatchExpression* filter, WorkingSet* ws, PlanStage* child);
        virtual ~KeepMutationsStage();

        virtual bool isEOF();
        virtual StageState work(WorkingSetID* out);

        virtual void prepareToYield();
        virtual void recoverFromYield();
        virtual void invalidate(const DiskLoc& dl, InvalidationType type);

        virtual PlanStageStats* getStats();

    private:
        // Not owned here.
        WorkingSet* _workingSet;

        scoped_ptr<PlanStage> _child;

        // Not owned here.  Should be the full query expression tree.
        const MatchExpression* _filter;

        // We read from our child...
        bool _doneReadingChild;

        // ...until it's out of results, at which point we put any flagged results back in the query
        // stream.
        bool _doneReturningFlagged;

        // Stats.
        CommonStats _commonStats;

        // Our copy of the working set's flagged results.
        std::vector<WorkingSetID> _flagged;

        // Iterator pointing into _flagged.
        std::vector<WorkingSetID>::const_iterator _flaggedIterator;
    };

}  // namespace mongo
