/**
 *    Copyright (C) 2018-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/collection_index_usage_tracker.h"
#include "mongo/db/pipeline/document_source.h"

namespace mongo {

/**
 * Provides a document source interface to retrieve index statistics for a given namespace.
 * Each document returned represents a single index and mongod instance.
 */
class DocumentSourceIndexStats final : public DocumentSource {
public:
    static constexpr StringData kStageName = "$indexStats"_sd;

    class LiteParsed final : public LiteParsedDocumentSource {
    public:
        static std::unique_ptr<LiteParsed> parse(const AggregationRequest& request,
                                                 const BSONElement& spec) {
            return std::make_unique<LiteParsed>(request.getNamespaceString());
        }

        explicit LiteParsed(NamespaceString nss) : _nss(std::move(nss)) {}

        stdx::unordered_set<NamespaceString> getInvolvedNamespaces() const final {
            return stdx::unordered_set<NamespaceString>();
        }

        PrivilegeVector requiredPrivileges(bool isMongos) const final {
            return {Privilege(ResourcePattern::forExactNamespace(_nss), ActionType::indexStats)};
        }

        bool isInitialSource() const final {
            return true;
        }

    private:
        const NamespaceString _nss;
    };

    // virtuals from DocumentSource
    const char* getSourceName() const final;
    Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;

    StageConstraints constraints(Pipeline::SplitState pipeState) const final {
        StageConstraints constraints(StreamType::kStreaming,
                                     PositionRequirement::kFirst,
                                     HostTypeRequirement::kAnyShard,
                                     DiskUseRequirement::kNoDiskUse,
                                     FacetRequirement::kNotAllowed,
                                     TransactionRequirement::kNotAllowed,
                                     LookupRequirement::kAllowed);

        constraints.requiresInputDocSource = false;
        return constraints;
    }

    boost::optional<DistributedPlanLogic> distributedPlanLogic() final {
        return boost::none;
    }

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

private:
    DocumentSourceIndexStats(const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
    GetNextResult doGetNext() final;

    CollectionIndexUsageMap _indexStatsMap;
    CollectionIndexUsageMap::const_iterator _indexStatsIter;
    std::string _processName;
};

}  // namespace mongo