/**
 *    Copyright (C) 2013 10gen 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"

namespace mongo {

    /**
     * This stage implements skip functionality.  It drops the first 'toSkip' results from its child
     * then returns the rest verbatim.
     *
     * Preconditions: None.
     */
    class SkipStage : public PlanStage {
    public:
        SkipStage(int toSkip, WorkingSet* ws, PlanStage* child);
        virtual ~SkipStage();

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

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

        virtual std::vector<PlanStage*> getChildren() const;

        virtual StageType stageType() const { return STAGE_SKIP; }

        virtual PlanStageStats* getStats();

        virtual const CommonStats* getCommonStats();

        virtual const SpecificStats* getSpecificStats();

        static const char* kStageType;

    private:
        WorkingSet* _ws;
        scoped_ptr<PlanStage> _child;

        // We drop the first _toSkip results that we would have returned.
        int _toSkip;

        // Stats
        CommonStats _commonStats;
        SkipStats _specificStats;
    };

}  // namespace mongo