text: /**
   *    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 <boost/optional.hpp>
  #include <map>
  #include <vector>
  
  #include "mongo/bson/bsonobj.h"
  #include "mongo/db/logical_session_id.h"
  #include "mongo/db/repl/oplog_entry.h"
  #include "mongo/util/uuid.h"
  
  namespace mongo {
  namespace repl {
  
  /**
   * Keeps tracks of oplog operations that would require changes to the config.transactions and
   * provides functions to create oplog entries that would contain the writes to update
   * config.transactions.
   *
   * Assumption: it is not allowed to do transactions/retryable writes against config.transactions.
   */
  class SessionUpdateTracker {
  public:
      /**
       * Converts all stored transaction infos to oplog writes to config.transactions.
       * Can return an empty vector if there is nothing to flush.
       */
      std::vector<OplogEntry> flushAll();
  
      /**
       * If 'entry' is part of a transaction, then return an update to the transaction table
       * corresponding to the operation. Otherwise, inspect the entry to determine whether to buffer
       * or flush the stored transaction information as part of retryable writes.
       */
      boost::optional<std::vector<OplogEntry>> updateSession(const OplogEntry& entry);
  
      /**
       * Returns true if the oplog entry represents an operation in a transaction and false otherwise.
       * No-ops representing migrated transactions are considered transaction operations.
       */
      static bool isTransactionEntry(const OplogEntry& entry);
  
  private:
      /**
       * Analyzes the given oplog entry and determines which transactions stored so far needs to be
       * converted to oplog writes.
       *
       * Note: should only be called when oplog entry's ns target config.transactions or config.$cmd.
       */
      std::vector<OplogEntry> _flush(const OplogEntry& entry);
  
      /**
       * Converts stored transaction infos that has a matching transcation id with the given
       * query predicate. Can return an empty vector if there is nothing to flush.
       */
      std::vector<OplogEntry> _flushForQueryPredicate(const BSONObj& queryPredicate);
  
      /**
       * Extract transaction information from the oplog if any and records them internally. Returns
       * a list of 'config.transactions' table updates to be flushed if 'entry' has a 'txnNumber'
       * greater than the currently stored session information.
       */
      boost::optional<std::vector<OplogEntry>> _updateSessionInfo(const OplogEntry& entry);
  
      /**
       * Inspects the oplog entry and determines whether this needs to update the session info or
       * flush stored transaction information to oplog writes.
       */
      boost::optional<std::vector<OplogEntry>> _updateOrFlush(const OplogEntry& entry);
  
      /**
       * Returns an update to the transaction table generated by a transaction operation. This returns
       * boost::none if the operation is a partialTxn operation that is not the first of the
       * transaction.
       */
      boost::optional<OplogEntry> _createTransactionTableUpdateFromTransactionOp(
          const repl::OplogEntry& entry);
  
      LogicalSessionIdMap<OplogEntry> _sessionsToUpdate;
  };
  
  }  // namespace repl
  }  // namespace mongo
  