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

namespace mongo {

    /**
     * This stage turns a RecordId into a BSONObj.
     *
     * In WorkingSetMember terms, it transitions from LOC_AND_IDX to LOC_AND_UNOWNED_OBJ by reading
     * the record at the provided loc.  Returns verbatim any data that already has an object.
     *
     * Preconditions: Valid RecordId.
     */
    class FetchStage : public PlanStage {
    public:
        FetchStage(OperationContext* txn,
                   WorkingSet* ws,
                   PlanStage* child,
                   const MatchExpression* filter,
                   const Collection* collection);

        virtual ~FetchStage();

        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);

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

        virtual StageType stageType() const { return STAGE_FETCH; }

        PlanStageStats* getStats();

        virtual const CommonStats* getCommonStats();

        virtual const SpecificStats* getSpecificStats();

        static const char* kStageType;

    private:

        /**
         * If the member (with id memberID) passes our filter, set *out to memberID and return that
         * ADVANCED.  Otherwise, free memberID and return NEED_TIME.
         */
        StageState returnIfMatches(WorkingSetMember* member, WorkingSetID memberID,
                                   WorkingSetID* out);

        OperationContext* _txn;

        // Collection which is used by this stage. Used to resolve record ids retrieved by child
        // stages. The lifetime of the collection must supersede that of the stage.
        const Collection* _collection;

        // _ws is not owned by us.
        WorkingSet* _ws;
        scoped_ptr<PlanStage> _child;

        // The filter is not owned by us.
        const MatchExpression* _filter;

        // 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.
        //
        // Some stages which request fetches don't need to use '_idBeingPagedIn' (e.g.,
        // CollectionScan) because they are implemented with an underlying iterator which keeps
        // track of the next WSM to be returned. A FetchStage has no such iterator, but rather
        // streams its results from the child. Therefore, when it requests a yield via NEED_FETCH,
        // the current WSM must be saved so that the fetched result can be returned on the next
        // call to work(). This also requires special invalidation handling not found in stages like
        // CollectionScan for when '_idBeingPagedIn' is invalidated before it can be returned.
        WorkingSetID _idBeingPagedIn;

        // Stats
        CommonStats _commonStats;
        FetchStats _specificStats;
    };

}  // namespace mongo