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.bookkeeper.metadata.etcd.helpers;
  
  import static java.nio.charset.StandardCharsets.UTF_8;
  
  import com.google.common.primitives.UnsignedBytes;
  import io.etcd.jetcd.ByteSequence;
  import io.etcd.jetcd.KV;
  import io.etcd.jetcd.KeyValue;
  import io.etcd.jetcd.options.GetOption;
  import java.util.Collections;
  import java.util.List;
  import java.util.concurrent.CompletableFuture;
  import java.util.function.Function;
  import java.util.stream.Collectors;
  import lombok.extern.slf4j.Slf4j;
  import org.apache.bookkeeper.common.concurrent.FutureUtils;
  
  /**
   * Read a range of key/value pairs in a streaming way.
   */
  @Slf4j
  public class KeyStream<T> {
  
      private final KV kvClient;
      private final ByteSequence startKey;
      private final ByteSequence endKey;
      private final Function<ByteSequence, T> encoder;
      private final int batchSize;
      private ByteSequence nextKey;
      private ByteSequence lastKey = null;
      private boolean hasMore = true;
  
      public KeyStream(KV kvClient,
                       ByteSequence startKey,
                       ByteSequence endKey,
                       Function<ByteSequence, T> encoder) {
          this(kvClient, startKey, endKey, encoder, 100);
      }
  
      public KeyStream(KV kvClient,
                       ByteSequence startKey,
                       ByteSequence endKey,
                       Function<ByteSequence, T> encoder,
                       int batchSize) {
          this.kvClient = kvClient;
          this.startKey = startKey;
          this.endKey = endKey;
          this.nextKey = startKey;
          this.encoder = encoder;
          this.batchSize = batchSize;
      }
  
      public CompletableFuture<List<T>> readNext() {
          ByteSequence beginKey;
          int batchSize = this.batchSize;
          synchronized (this) {
              if (!hasMore) {
                  return FutureUtils.value(Collections.emptyList());
              }
  
              beginKey = nextKey;
              if (null != lastKey) {
                  // read one more in since we are including last key.
                  batchSize += 1;
              }
          }
          if (log.isTraceEnabled()) {
              log.trace("Read keys between {} and {}", beginKey.toString(UTF_8), endKey.toString(UTF_8));
          }
          return kvClient.get(
              beginKey,
              GetOption.newBuilder()
                  .withRange(endKey)
                  .withKeysOnly(true)
                  .withLimit(batchSize)
                  .withSortField(GetOption.SortTarget.KEY)
                  .withSortOrder(GetOption.SortOrder.ASCEND)
                  .build()
          ).thenApply(getResp -> {
              List<KeyValue> kvs = getResp.getKvs();
              ByteSequence lkey;
              synchronized (KeyStream.this) {
                  hasMore = getResp.isMore();
                  lkey = lastKey;
                  if (kvs.size() > 0) {
                      lastKey = nextKey = kvs.get(kvs.size() - 1).getKey();
                  }
              }
              if (null != lkey
                  && kvs.size() > 0
                  && UnsignedBytes.lexicographicalComparator().compare(
                      lkey.getBytes(),
                      kvs.get(0).getKey().getBytes()) == 0) {
                  kvs.remove(0);
              }
              return kvs.stream()
                  .map(kv -> encoder.apply(kv.getKey()))
                  .collect(Collectors.toList());
          });
      }
  
  }
  