/**
 * Copyright (C) 2017 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/pipeline/document_source.h"
#include "mongo/db/pipeline/document_source_single_document_transformation.h"
#include "mongo/db/pipeline/document_sources_gen.h"

namespace mongo {

/**
 * The $changeStream stage is an alias for a cursor on oplog followed by a $match stage and a
 * transform stage on mongod.
 */
class DocumentSourceChangeStream final {
public:
    class LiteParsed final : public LiteParsedDocumentSource {
    public:
        static std::unique_ptr<LiteParsed> parse(const AggregationRequest& request,
                                                 const BSONElement& spec) {
            return stdx::make_unique<LiteParsed>();
        }

        bool isChangeStream() const final {
            return true;
        }

        stdx::unordered_set<NamespaceString> getInvolvedNamespaces() const final {
            // TODO SERVER-29138: we need to communicate that this stage will need to look up
            // documents from different collections.
            return stdx::unordered_set<NamespaceString>();
        }

        // TODO SERVER-29138: Add required privileges.
        PrivilegeVector requiredPrivileges(bool isMongos) const final {
            return {};
        }

        bool allowedToForwardFromMongos() const final {
            return false;
        }
    };

    class Transformation : public DocumentSourceSingleDocumentTransformation::TransformerInterface {
    public:
        Transformation(BSONObj changeStreamSpec) : _changeStreamSpec(changeStreamSpec.getOwned()) {}
        ~Transformation() = default;
        Document applyTransformation(const Document& input) final;
        TransformerType getType() const final {
            return TransformerType::kChangeStreamTransformation;
        };
        void optimize() final{};
        Document serializeStageOptions(
            boost::optional<ExplainOptions::Verbosity> explain) const final;
        DocumentSource::GetDepsReturn addDependencies(DepsTracker* deps) const final;
        DocumentSource::GetModPathsReturn getModifiedPaths() const final;

    private:
        BSONObj _changeStreamSpec;
    };

    // The name of the field where the document key (_id and shard key, if present) will be found
    // after the transformation.
    static constexpr StringData kDocumentKeyField = "documentKey"_sd;

    // The name of the field where the full document will be found after the transformation. The
    // full document is only present for certain types of operations, such as an insert.
    static constexpr StringData kFullDocumentField = "fullDocument"_sd;

    // The name of the field where the change identifier will be located after the transformation.
    static constexpr StringData kIdField = "_id"_sd;

    // The name of the field where the namespace of the change will be located after the
    // transformation.
    static constexpr StringData kNamespaceField = "ns"_sd;

    // The name of the field where the type of the operation will be located after the
    // transformation.
    static constexpr StringData kOperationTypeField = "operationType"_sd;

    // The name of this stage.
    static constexpr StringData kStageName = "$changeStream"_sd;

    // The name of the field where the clusterTime of the change will be located after the
    // transformation. The cluster time will be located inside the change identifier, so the full
    // path to the cluster time will be kIdField + "." + kClusterTimeField.
    static constexpr StringData kClusterTimeField = "clusterTime"_sd;

    // The name of the field where the timestamp of the change will be located after the
    // transformation. The timestamp will be located inside the cluster time, so the full path
    // to the timestamp will be kIdField + "." + kClusterTimeField + "." + kTimestampField.
    static constexpr StringData kTimestampField = "ts"_sd;

    // The different types of operations we can use for the operation type.
    static constexpr StringData kUpdateOpType = "update"_sd;
    static constexpr StringData kDeleteOpType = "delete"_sd;
    static constexpr StringData kReplaceOpType = "replace"_sd;
    static constexpr StringData kInsertOpType = "insert"_sd;
    static constexpr StringData kInvalidateOpType = "invalidate"_sd;

    /**
     * Produce the BSON object representing the filter for the $match stage to filter oplog entries
     * to only those relevant for this $changeStream stage.
     */
    static BSONObj buildMatchFilter(const NamespaceString& nss, Timestamp startFrom, bool isResume);

    /**
     * Parses a $changeStream stage from 'elem' and produces the $match and transformation
     * stages required.
     */
    static std::list<boost::intrusive_ptr<DocumentSource>> createFromBson(
        BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& expCtx);

    static boost::intrusive_ptr<DocumentSource> createTransformationStage(
        BSONObj changeStreamSpec, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);

private:
    // It is illegal to construct a DocumentSourceChangeStream directly, use createFromBson()
    // instead.
    DocumentSourceChangeStream() = default;
};

}  // namespace mongo