/**
 *    Copyright (C) 2022-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 "mongo/db/pipeline/document_source.h"

namespace mongo {


class DocumentSourceSetVariableFromSubPipeline final : public DocumentSource {
public:
    static constexpr StringData kStageName = "$setVariableFromSubPipeline"_sd;

    static boost::intrusive_ptr<DocumentSource> createFromBson(
        BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& expCtx);

    static boost::intrusive_ptr<DocumentSourceSetVariableFromSubPipeline> create(
        const boost::intrusive_ptr<ExpressionContext>& expCtx,
        std::unique_ptr<Pipeline, PipelineDeleter> subpipeline,
        Variables::Id varID);

    ~DocumentSourceSetVariableFromSubPipeline() = default;

    boost::optional<DistributedPlanLogic> distributedPlanLogic() final {
        // {shardsStage, mergingStage, sortPattern}
        return DistributedPlanLogic{nullptr, this, boost::none};
    }
    const char* getSourceName() const final {
        return kStageName.rawData();
    }
    StageConstraints constraints(Pipeline::SplitState) const final {
        StageConstraints setVariableConstraints(StreamType::kStreaming,
                                                PositionRequirement::kNone,
                                                // Set variable can run anywhere as long as it is
                                                // in the merging half of the pipeline.
                                                HostTypeRequirement::kNone,
                                                DiskUseRequirement::kNoDiskUse,
                                                FacetRequirement::kNotAllowed,
                                                TransactionRequirement::kNotAllowed,
                                                LookupRequirement::kAllowed,
                                                UnionRequirement::kAllowed);

        // The constraints of the sub-pipeline determine the constraints of the
        // $setVariableFromSubPipeline. We want to forward the strictest requirements of the stages
        // in the sub-pipeline.
        if (_subPipeline) {
            setVariableConstraints = StageConstraints::getStrictestConstraints(
                _subPipeline->getSources(), setVariableConstraints);
        }
        // This stage doesn't modify documents.
        setVariableConstraints.preservesOrderAndMetadata = true;
        return setVariableConstraints;
    }

    std::list<boost::intrusive_ptr<mongo::DocumentSource>>* getSubPipeline() const override {
        return &_subPipeline->getSources();
    }

    auto variableId() const {
        return _variableID;
    }

    DepsTracker::State getDependencies(DepsTracker* deps) const final;

    /**
     * Set the sub-pipeline's initial source. Similar to Pipeline's addInitialSource().
     * Should be used to add a cursor/document generating stage to the pipeline.
     */
    void addSubPipelineInitialSource(boost::intrusive_ptr<DocumentSource> source);

protected:
    DocumentSourceSetVariableFromSubPipeline(const boost::intrusive_ptr<ExpressionContext>& expCtx,
                                             std::unique_ptr<Pipeline, PipelineDeleter> subpipeline,
                                             Variables::Id varID)
        : DocumentSource(kStageName, expCtx),
          _subPipeline(std::move(subpipeline)),
          _variableID(varID) {}


private:
    GetNextResult doGetNext() final;
    Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
    std::unique_ptr<Pipeline, PipelineDeleter> _subPipeline;
    Variables::Id _variableID;
    // $setVariableFromSubPipeline sets the value of $$SEARCH_META only on the first call to
    // doGetNext().
    bool _firstCallForInput = true;
};
}  // namespace mongo