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/**
 *    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/exec/plan_stage.h"
#include "mongo/db/index/index_access_method.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/matcher/expression.h"
#include "mongo/db/query/index_bounds.h"
#include "mongo/db/record_id.h"
#include "mongo/platform/unordered_set.h"

namespace mongo {

class IndexAccessMethod;
class IndexDescriptor;
class WorkingSet;

struct DistinctParams {
    DistinctParams() : descriptor(NULL), direction(1), fieldNo(0) {}

    // What index are we traversing?
    const IndexDescriptor* descriptor;

    // And in what direction?
    int direction;

    // What are the bounds?
    IndexBounds bounds;

    // What field in the index's key pattern is the one we're distinct-ing over?
    // For example:
    // If we have an index {a:1, b:1} we could use it to distinct over either 'a' or 'b'.
    // If we distinct over 'a' the position is 0.
    // If we distinct over 'b' the position is 1.
    int fieldNo;
};

/**
 * Used by the distinct command.  Executes a mutated index scan over the provided bounds.
 * However, rather than looking at every key in the bounds, it skips to the next value of the
 * _params.fieldNo-th indexed field.  This is because distinct only cares about distinct values
 * for that field, so there is no point in examining all keys with the same value for that
 * field.
 *
 * Only created through the getExecutorDistinct path.  See db/query/get_executor.cpp
 */
class DistinctScan : public PlanStage {
public:
    DistinctScan(OperationContext* txn, const DistinctParams& params, WorkingSet* workingSet);
    virtual ~DistinctScan() {}

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

    virtual PlanStageStats* getStats();

    virtual const CommonStats* getCommonStats() const;

    virtual const SpecificStats* getSpecificStats() const;

    static const char* kStageType;

private:
    // transactional context for read locks. Not owned by us
    OperationContext* _txn;

    // The WorkingSet we annotate with results.  Not owned by us.
    WorkingSet* _workingSet;

    // Index access.
    const IndexDescriptor* _descriptor;  // owned by Collection -> IndexCatalog
    const IndexAccessMethod* _iam;       // owned by Collection -> IndexCatalog

    // The cursor we use to navigate the tree.
    std::unique_ptr<SortedDataInterface::Cursor> _cursor;

    DistinctParams _params;

    // _checker gives us our start key and ensures we stay in bounds.
    IndexBoundsChecker _checker;
    IndexSeekPoint _seekPoint;

    // Stats
    CommonStats _commonStats;
    DistinctScanStats _specificStats;
};

}  // namespace mongo