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.timeline;
  
  import java.util.Iterator;
  import java.util.Objects;
  
  
  /**
   * This is a mutable reference to an immutable object. It can be snapshotted.
   * <br>
   * This class requires external synchronization.
   */
  public final class TimelineObject<T> implements Revertable {
      static class ObjectContainer<T> implements Delta {
          private T value;
  
          ObjectContainer(T initialValue) {
              this.value = initialValue;
          }
  
          T value() {
              return value;
          }
  
          void setValue(T value) {
              this.value = value;
          }
  
          @Override
          public void mergeFrom(long destinationEpoch, Delta delta) {
              // Nothing to do
          }
      }
  
      private final SnapshotRegistry snapshotRegistry;
      private final T initialValue;
      private T value;
  
      public TimelineObject(SnapshotRegistry snapshotRegistry, T initialValue) {
          Objects.requireNonNull(initialValue);
          this.snapshotRegistry = snapshotRegistry;
          this.initialValue = initialValue;
          this.value = initialValue;
          snapshotRegistry.register(this);
      }
  
      public T get() {
          return value;
      }
  
      public T get(long epoch) {
          if (epoch == SnapshotRegistry.LATEST_EPOCH) return value;
          Iterator<Snapshot> iterator = snapshotRegistry.iterator(epoch);
          while (iterator.hasNext()) {
              Snapshot snapshot = iterator.next();
              ObjectContainer<T> container = snapshot.getDelta(TimelineObject.this);
              if (container != null) return container.value();
          }
          return value;
      }
  
      public void set(T newValue) {
          Objects.requireNonNull(newValue);
          Iterator<Snapshot> iterator = snapshotRegistry.reverseIterator();
          if (iterator.hasNext()) {
              Snapshot snapshot = iterator.next();
              ObjectContainer<T> prevContainer = snapshot.getDelta(TimelineObject.this);
              if (prevContainer == null) {
                  prevContainer = new ObjectContainer<>(initialValue);
                  snapshot.setDelta(TimelineObject.this, prevContainer);
                  prevContainer.setValue(value);
              }
          }
          this.value = newValue;
      }
  
      @SuppressWarnings("unchecked")
      @Override
      public void executeRevert(long targetEpoch, Delta delta) {
          ObjectContainer<T> container = (ObjectContainer<T>) delta;
          this.value = container.value();
      }
  
      @Override
      public void reset() {
          set(initialValue);
      }
  
      @Override
      public int hashCode() {
          return value.hashCode();
      }
  
      @Override
      public boolean equals(Object o) {
          if (!(o instanceof TimelineObject<?> other)) return false;
          return value.equals(other.value);
      }
  
      @Override
      public String toString() {
          return value.toString();
      }
  }
  