/**
 *    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 <queue>

#include "mongo/db/exec/plan_stage.h"
#include "mongo/db/exec/working_set.h"

namespace mongo {

    class RecordId;

    /**
     * QueuedDataStage is a data-producing stage.  Unlike the other two leaf stages (CollectionScan
     * and IndexScan) QueuedDataStage does not require any underlying storage layer.
     *
     * A QueuedDataStage is "programmed" by pushing return values from work() onto its internal
     * queue.  Calls to QueuedDataStage::work() pop values off that queue and return them in FIFO
     * order, annotating the working set with data when appropriate.
     */
    class QueuedDataStage : public PlanStage {
    public:
        QueuedDataStage(WorkingSet* ws);
        virtual ~QueuedDataStage() { }

        virtual StageState work(WorkingSetID* out);

        virtual bool isEOF();

        // These don't really mean anything here.
        // Some day we could count the # of calls to the yield functions to check that other stages
        // have correct yielding behavior.
        virtual void saveState();
        virtual void restoreState(OperationContext* opCtx);
        virtual void invalidate(OperationContext* txn, const RecordId& dl, InvalidationType type);

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

        virtual StageType stageType() const { return STAGE_QUEUED_DATA; }

        //
        // Exec stats
        //

        virtual PlanStageStats* getStats();

        virtual const CommonStats* getCommonStats() const;

        virtual const SpecificStats* getSpecificStats() const;

        /**
         * Add a result to the back of the queue.
         *
         * Note: do not add PlanStage::ADVANCED with this method, ADVANCED can
         * only be added with a data member.
         *
         * Work() goes through the queue.
         * Either no data is returned (just a state), or...
         */
        void pushBack(const PlanStage::StageState state);

        /**
         * ...data is returned (and we ADVANCED)
         *
         * Allocates a new member and copies 'member' into it.
         * Does not take ownership of anything in 'member'.
         */
        void pushBack(const WorkingSetMember& member);

        static const char* kStageType;

    private:
        // We don't own this.
        WorkingSet* _ws;

        // The data we return.
        std::queue<PlanStage::StageState> _results;
        std::queue<WorkingSetID> _members;

        // Stats
        CommonStats _commonStats;
        MockStats _specificStats;
    };

}  // namespace mongo