text: /**
   *    Copyright (C) 2019-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 <boost/optional.hpp>
  #include <string>
  #include <vector>
  
  #include "mongo/base/string_data.h"
  #include "mongo/db/namespace_string.h"
  #include "mongo/db/pipeline/document_source_merge_modes_gen.h"
  
  namespace mongo {
  class BSONObjBuilder;
  class BSONElement;
  
  // Defines a policy strategy describing what to do when there is a matching document in the target
  // collection. Can hold a value from the MergeWhenMatchedModeEnum, or a custom pipeline definition.
  struct MergeWhenMatchedPolicy {
      MergeWhenMatchedModeEnum mode;
      boost::optional<std::vector<BSONObj>> pipeline;
  };
  
  /**
   * Serialize and deserialize functions for the $merge stage 'into' field which can be a single
   * string value, or an object.
   */
  void mergeTargetNssSerializeToBSON(const NamespaceString& targetNss,
                                     StringData fieldName,
                                     BSONObjBuilder* bob);
  NamespaceString mergeTargetNssParseFromBSON(const BSONElement& elem);
  
  /**
   * Serialize and deserialize functions for the $merge stage 'on' field which can be a single string
   * value, or array of strings.
   */
  void mergeOnFieldsSerializeToBSON(const std::vector<std::string>& fields,
                                    StringData fieldName,
                                    BSONObjBuilder* bob);
  std::vector<std::string> mergeOnFieldsParseFromBSON(const BSONElement& elem);
  
  /**
   * Serialize and deserialize functions for the $merge stage 'whenMatched' field which can be either
   * a string value, or an array of objects defining a custom pipeline.
   */
  void mergeWhenMatchedSerializeToBSON(const MergeWhenMatchedPolicy& policy,
                                       StringData fieldName,
                                       BSONObjBuilder* bob);
  MergeWhenMatchedPolicy mergeWhenMatchedParseFromBSON(const BSONElement& elem);
  }  // namespace mongo
  