/**
 *    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 <vector>

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

namespace mongo {

/**
 * Reads from N children, each of which must have a valid RecordId.  Uses a hash table to
 * intersect the outputs of the N children, and outputs the intersection.
 *
 * Preconditions: Valid RecordId.  More than one child.
 *
 * Any RecordId that we keep a reference to that is invalidated before we are able to return it
 * is fetched and added to the WorkingSet as "flagged for further review."  Because this stage
 * operates with RecordIds, we are unable to evaluate the AND for the invalidated RecordId, and it
 * must be fully matched later.
 */
class AndHashStage : public PlanStage {
public:
    AndHashStage(WorkingSet* ws, const Collection* collection);

    /**
     * For testing only. Allows tests to set memory usage threshold.
     */
    AndHashStage(WorkingSet* ws, const Collection* collection, size_t maxMemUsage);

    virtual ~AndHashStage();

    void addChild(PlanStage* child);

    /**
     * Returns memory usage.
     * For testing only.
     */
    size_t getMemUsage() const;

    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_AND_HASH;
    }

    virtual PlanStageStats* getStats();

    virtual const CommonStats* getCommonStats() const;

    virtual const SpecificStats* getSpecificStats() const;

    static const char* kStageType;

private:
    static const size_t kLookAheadWorks;

    StageState readFirstChild(WorkingSetID* out);
    StageState hashOtherChildren(WorkingSetID* out);
    StageState workChild(size_t childNo, WorkingSetID* out);

    // Not owned by us.
    const Collection* _collection;

    // Not owned by us.
    WorkingSet* _ws;

    // The stages we read from.  Owned by us.
    std::vector<PlanStage*> _children;

    // We want to see if any of our children are EOF immediately.  This requires working them a
    // few times to see if they hit EOF or if they produce a result.  If they produce a result,
    // we place that result here.
    std::vector<WorkingSetID> _lookAheadResults;

    // _dataMap is filled out by the first child and probed by subsequent children.  This is the
    // hash table that we create by intersecting _children and probe with the last child.
    typedef unordered_map<RecordId, WorkingSetID, RecordId::Hasher> DataMap;
    DataMap _dataMap;

    // Keeps track of what elements from _dataMap subsequent children have seen.
    // Only used while _hashingChildren.
    typedef unordered_set<RecordId, RecordId::Hasher> SeenMap;
    SeenMap _seenMap;

    // True if we're still intersecting _children[0..._children.size()-1].
    bool _hashingChildren;

    // Which child are we currently working on?
    size_t _currentChild;

    // Stats
    CommonStats _commonStats;
    AndHashStats _specificStats;

    // The usage in bytes of all buffered data that we're holding.
    // Memory usage is calculated from keys held in _dataMap only.
    // For simplicity, results in _lookAheadResults do not count towards the limit.
    size_t _memUsage;

    // Upper limit for buffered data memory usage.
    // Defaults to 32 MB (See kMaxBytes in and_hash.cpp).
    size_t _maxMemUsage;
};

}  // namespace mongo