content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements. See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License. You may obtain a copy of the License at
   *
   *    http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.kafka.raft.internals;
  
  import org.apache.kafka.raft.VoterSet;
  import org.apache.kafka.server.common.KRaftVersion;
  
  import java.util.Optional;
  
  /**
   * KRaftVersionUpgrade is a sum types for coordinating the upgrade of the kraft version.
   *
   * {@code Voters} is used to stored in-memory the latest voter set. {@code Version} is used to
   * store in-memory the upgraded kraft version.
   *
   * This type makes it possible to upgrade the kraft version by only using compare-and-swap and
   * avoid blocking locks.
   */
  public sealed interface KRaftVersionUpgrade {
      public record Empty() implements KRaftVersionUpgrade {
      }
  
      public record Version(KRaftVersion kraftVersion) implements KRaftVersionUpgrade {
      }
  
      public record Voters(VoterSet voters) implements KRaftVersionUpgrade {
      }
  
      public default Optional<Voters> toVoters() {
          if (this instanceof Voters) {
              return Optional.of(((Voters) this));
          } else {
              return Optional.empty();
          }
      }
  
      public default Optional<Version> toVersion() {
          if (this instanceof Version) {
              return Optional.of(((Version) this));
          } else {
              return Optional.empty();
          }
      }
  
      static final KRaftVersionUpgrade EMPTY = new Empty();
  
      public static KRaftVersionUpgrade empty() {
          return EMPTY;
      }
  
  }
  