/**
 *    Copyright (C) 2020-present MongoDB, Inc.
 *
 *    This program is free software: you can redistribute it and/or modify
 *    it under the terms of the Server Side Public License, version 1,
 *    as published by MongoDB, Inc.
 *
 *    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
 *    Server Side Public License for more details.
 *
 *    You should have received a copy of the Server Side Public License
 *    along with this program. If not, see
 *    <http://www.mongodb.com/licensing/server-side-public-license>.
 *
 *    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 Server Side 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/sbe/stages/stages.h"

namespace mongo::sbe {
/**
 * This stage deduplicates by a given key. Unlike a HashAgg, this stage is not blocking and rows are
 * returned in the same order as they appear in the input stream.
 *
 * TODO: It is possible to optimize this stage in the case where the input is sorted by key X, we
 * are "uniquing" by key Y, and we are guaranteed that all identical values of Y appear are
 * associated with the same key X. In this case the hash table of seen elements can be cleared each
 * time a new key X is encountered.
 *
 * For example, this optimization is possible when the UniqueStage is uniquing by record ID and
 * below it there are non-multikey index scans merged via a SortMerge stage. Each duplicate record
 * ID will be associated with the same sort key.
 *
 * Debug string representation:
 *
 *   unique [<keys>] childStage
 */
class UniqueStage final : public PlanStage {
public:
    UniqueStage(std::unique_ptr<PlanStage> input,
                value::SlotVector keys,
                PlanNodeId planNodeId,
                bool participateInTrialRunTracking = true);

    std::unique_ptr<PlanStage> clone() const final;

    void prepare(CompileCtx& ctx) final;
    value::SlotAccessor* getAccessor(CompileCtx& ctx, value::SlotId slot) final;
    void open(bool reOpen) final;
    PlanState getNext() final;
    void close() final;

    std::unique_ptr<PlanStageStats> getStats(bool includeDebugInfo) const final;
    const SpecificStats* getSpecificStats() const final;
    std::vector<DebugPrinter::Block> debugPrint() const final;
    size_t estimateCompileTimeSize() const final;

private:
    const value::SlotVector _keySlots;

    std::vector<value::SlotAccessor*> _inKeyAccessors;

    // Table of keys that have been seen.
    stdx::unordered_set<value::MaterializedRow,
                        value::MaterializedRowHasher,
                        value::MaterializedRowEq>
        _seen;
    UniqueStats _specificStats;
};
}  // namespace mongo::sbe