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.beam.runners.samza.runtime;
  
  import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkState;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.concurrent.CompletableFuture;
  import java.util.concurrent.CompletionStage;
  import java.util.concurrent.atomic.AtomicBoolean;
  import org.apache.beam.runners.samza.util.FutureUtils;
  import org.apache.beam.sdk.values.WindowedValue;
  
  class FutureCollectorImpl<OutT> implements FutureCollector<OutT> {
    private final AtomicBoolean collectorSealed;
    private CompletionStage<Collection<WindowedValue<OutT>>> outputFuture;
  
    FutureCollectorImpl() {
      outputFuture = CompletableFuture.completedFuture(new ArrayList<>());
      collectorSealed = new AtomicBoolean(true);
    }
  
    @Override
    public void add(CompletionStage<WindowedValue<OutT>> element) {
      checkState(
          !collectorSealed.get(),
          "Cannot add element to an unprepared collector. Make sure prepare() is invoked before adding elements.");
  
      // We need synchronize guard against scenarios when watermark/finish bundle trigger outputs.
      synchronized (this) {
        outputFuture =
            outputFuture.thenCombine(
                element,
                (collection, event) -> {
                  collection.add(event);
                  return collection;
                });
      }
    }
  
    @Override
    public void addAll(CompletionStage<Collection<WindowedValue<OutT>>> elements) {
      checkState(
          !collectorSealed.get(),
          "Cannot add elements to an unprepared collector. Make sure prepare() is invoked before adding elements.");
  
      synchronized (this) {
        outputFuture = FutureUtils.combineFutures(outputFuture, elements);
      }
    }
  
    @Override
    public void discard() {
      collectorSealed.compareAndSet(false, true);
  
      synchronized (this) {
        outputFuture = CompletableFuture.completedFuture(new ArrayList<>());
      }
    }
  
    @Override
    public CompletionStage<Collection<WindowedValue<OutT>>> finish() {
      /*
       * We can ignore the results here because its okay to call finish without invoking prepare. It will be a no-op
       * and an empty collection will be returned.
       */
      collectorSealed.compareAndSet(false, true);
  
      synchronized (this) {
        final CompletionStage<Collection<WindowedValue<OutT>>> sealedOutputFuture = outputFuture;
        outputFuture = CompletableFuture.completedFuture(new ArrayList<>());
        return sealedOutputFuture;
      }
    }
  
    @Override
    public void prepare() {
      boolean isCollectorSealed = collectorSealed.compareAndSet(true, false);
      checkState(
          isCollectorSealed,
          "Failed to prepare the collector. Collector needs to be sealed before prepare() is invoked.");
    }
  }
  