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 java.util.Optional;
  
  /**
   * An object that tracks values of {@code T} at different offsets.
   */
  public interface LogHistory<T> {
      /**
       * Add a new value at a given offset.
       *
       * The provided {@code offset} must be greater than or equal to 0 and must be greater than the
       * offset of all previous calls to this method.
       *
       * @param offset the offset
       * @param value the value to store
       * @throws IllegalArgumentException if the offset is not greater than all previous offsets
       */
      void addAt(long offset, T value);
  
      /**
       * Returns the value that has the largest offset that is less than or equal to the provided
       * offset.
       *
       * @param offset the offset
       * @return the value if it exists, otherwise {@code Optional.empty()}
       */
      Optional<T> valueAtOrBefore(long offset);
  
      /**
       * Returns the value with the largest offset.
       *
       * @return the value if it exists, otherwise {@code Optional.empty()}
       */
      Optional<Entry<T>> lastEntry();
  
      /**
       * Removes all entries with an offset greater than or equal to {@code endOffset}.
       *
       * @param endOffset the ending offset
       */
      void truncateNewEntries(long endOffset);
  
      /**
       * Removes all entries but the last entry that has an offset that is less than or equal to
       * {@code startOffset}.
       *
       * This operation does not remove the entry with the largest offset that is less than or equal
       * to {@code startOffset}. This is needed so that calls to {@code valueAtOrBefore} and
       * {@code lastEntry} always return a non-empty value if a value was previously added to this
       * object.
       *
       * @param startOffset the starting offset
       */
      void truncateOldEntries(long startOffset);
  
      /**
       * Removes all the values from this object.
       */
      void clear();
  
      record Entry<T>(long offset, T value) { }
  }
  