/**
 *    Copyright (C) 2013-2014 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/fts/fts_index_format.h"
#include "mongo/db/fts/fts_matcher.h"
#include "mongo/db/fts/fts_query.h"
#include "mongo/db/fts/fts_spec.h"
#include "mongo/db/fts/fts_util.h"
#include "mongo/db/index/index_descriptor.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/matcher/expression.h"
#include "mongo/db/record_id.h"
#include "mongo/platform/unordered_map.h"

#include <map>
#include <queue>
#include <vector>

namespace mongo {

using fts::FTSIndexFormat;
using fts::FTSMatcher;
using fts::FTSQuery;
using fts::FTSSpec;
using fts::MAX_WEIGHT;

class OperationContext;

struct TextStageParams {
    TextStageParams(const FTSSpec& s) : spec(s) {}

    // Text index descriptor.  IndexCatalog owns this.
    IndexDescriptor* index;

    // Index spec.
    FTSSpec spec;

    // Index keys that precede the "text" index key.
    BSONObj indexPrefix;

    // The text query.
    FTSQuery query;
};

/**
 * Implements a blocking stage that returns text search results.
 *
 * Prerequisites: None; is a leaf node.
 * Output type: LOC_AND_OBJ_UNOWNED.
 *
 * TODO: Should the TextStage ever generate NEED_YIELD requests for fetching MMAP v1 records?
 * Right now this stage could reduce concurrency by failing to request a yield during fetch.
 */
class TextStage : public PlanStage {
public:
    /**
     * The text stage has a few 'states' it transitions between.
     */
    enum State {
        // 1. Initialize the index scans we use to retrieve term/score info.
        INIT_SCANS,

        // 2. Read the terms/scores from the text index.
        READING_TERMS,

        // 3. Return results to our parent.
        RETURNING_RESULTS,

        // 4. Done.
        DONE,
    };

    TextStage(OperationContext* txn,
              const TextStageParams& params,
              WorkingSet* ws,
              const MatchExpression* filter);

    virtual ~TextStage();

    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_TEXT;
    }

    PlanStageStats* getStats();

    virtual const CommonStats* getCommonStats() const;

    virtual const SpecificStats* getSpecificStats() const;

    static const char* kStageType;

private:
    /**
     * Initializes sub-scanners.
     */
    StageState initScans(WorkingSetID* out);

    /**
     * Helper for buffering results array.  Returns NEED_TIME (if any results were produced),
     * IS_EOF, or FAILURE.
     */
    StageState readFromSubScanners(WorkingSetID* out);

    /**
     * Helper called from readFromSubScanners to update aggregate score with a new-found (term,
     * score) pair for this document.  Also rejects documents that don't match this stage's
     * filter.
     */
    StageState addTerm(WorkingSetID wsid, WorkingSetID* out);

    /**
     * Possibly return a result.  FYI, this may perform a fetch directly if it is needed to
     * evaluate all filters.
     */
    StageState returnResults(WorkingSetID* out);

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

    // Parameters of this text stage.
    TextStageParams _params;

    // Text-specific phrase and negated term matcher.
    FTSMatcher _ftsMatcher;

    // Working set. Not owned by us.
    WorkingSet* _ws;

    // Filter. Not owned by us.
    const MatchExpression* _filter;

    // Stats.
    CommonStats _commonStats;
    TextStats _specificStats;

    // What state are we in?  See the State enum above.
    State _internalState;

    // Used in INIT_SCANS and READING_TERMS.  The index scans we're using to retrieve text
    // terms.
    OwnedPointerVector<PlanStage> _scanners;

    // Which _scanners are we currently reading from?
    size_t _currentIndexScanner;

    // If not Null, we use this rather than asking our child what to do next.
    WorkingSetID _idRetrying;

    // Map each buffered record id to this data.
    struct TextRecordData {
        TextRecordData() : wsid(WorkingSet::INVALID_ID), score(0.0) {}
        WorkingSetID wsid;
        double score;
    };

    // Temporary score data filled out by sub-scans.  Used in READING_TERMS and
    // RETURNING_RESULTS.
    // Maps from diskloc -> (aggregate score for doc, wsid).
    typedef unordered_map<RecordId, TextRecordData, RecordId::Hasher> ScoreMap;
    ScoreMap _scores;
    ScoreMap::const_iterator _scoreIterator;

    // Used for fetching records from the collection.
    std::unique_ptr<RecordCursor> _recordCursor;
};

}  // namespace mongo