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.distributedlog.logsegment;
  
  import com.google.common.annotations.Beta;
  import java.util.List;
  import java.util.concurrent.CompletableFuture;
  import org.apache.distributedlog.Entry;
  import org.apache.distributedlog.LogSegmentMetadata;
  import org.apache.distributedlog.io.AsyncCloseable;
  
  /**
   * An interface class to read the enveloped entry (serialized bytes of
   * {@link org.apache.distributedlog.Entry}) from a log segment.
   */
  @Beta
  public interface LogSegmentEntryReader extends AsyncCloseable {
      /**
       * An interface Listener for StateChange.
       */
      interface StateChangeListener {
  
          /**
           * Notify when caught up on inprogress.
           */
          void onCaughtupOnInprogress();
  
      }
  
      /**
       * Start the reader. The method to signal the implementation
       * to start preparing the data for consumption {@link #readNext(int)}
       */
      void start();
  
      /**
       * Register the state change listener.
       *
       * @param listener register the state change listener
       * @return entry reader
       */
      LogSegmentEntryReader registerListener(StateChangeListener listener);
  
      /**
       * Unregister the state change listener.
       *
       * @param listener register the state change listener
       * @return entry reader
       */
      LogSegmentEntryReader unregisterListener(StateChangeListener listener);
  
      /**
       * Return the log segment metadata for this reader.
       *
       * @return the log segment metadata
       */
      LogSegmentMetadata getSegment();
  
      /**
       * Update the log segment each time when the metadata has changed.
       *
       * @param segment new metadata of the log segment.
       */
      void onLogSegmentMetadataUpdated(LogSegmentMetadata segment);
  
      /**
       * Read next <i>numEntries</i> entries from current log segment.
       *
       *  <p><i>numEntries</i> will be best-effort.
       *
       * @param numEntries num entries to read from current log segment
       * @return A promise that when satisfied will contain a non-empty list of entries with their content.
       * @throw {@link org.apache.distributedlog.exceptions.EndOfLogSegmentException} when
       *          read entries beyond the end of a <i>closed</i> log segment.
       */
      CompletableFuture<List<Entry.Reader>> readNext(int numEntries);
  
      /**
       * Return the last add confirmed entry id (LAC).
       *
       * @return the last add confirmed entry id.
       */
      long getLastAddConfirmed();
  
      /**
       * Is the reader reading beyond last add confirmed.
       *
       * @return true if the reader is reading beyond last add confirmed
       */
      boolean isBeyondLastAddConfirmed();
  
      /**
       * Has the log segment reader caught up with the inprogress log segment.
       *
       * @return true only if the log segment is inprogress and it is caught up, otherwise return false.
       */
      boolean hasCaughtUpOnInprogress();
  
  }
  