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.core;
  
  import java.util.Collections;
  import java.util.Set;
  import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
  import org.apache.beam.sdk.values.PCollectionView;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Sets;
  
  /**
   * A {@link SideInputReader} representing a well-defined set of views, but not storing any values
   * for them. Used to check if a side input is present when the data itself comes from elsewhere.
   */
  public class NullSideInputReader implements SideInputReader {
  
    /** The default empty instance. */
    private static final NullSideInputReader EMPTY_INSTANCE = of(Collections.emptySet());
  
    private Set<PCollectionView<?>> views;
  
    public static NullSideInputReader empty() {
      return EMPTY_INSTANCE;
    }
  
    public static NullSideInputReader of(Iterable<? extends PCollectionView<?>> views) {
      return new NullSideInputReader(views);
    }
  
    private NullSideInputReader(Iterable<? extends PCollectionView<?>> views) {
      this.views = Sets.newHashSet(views);
    }
  
    @Override
    public <T> T get(PCollectionView<T> view, BoundedWindow window) {
      throw new IllegalArgumentException("cannot call NullSideInputReader.get()");
    }
  
    @Override
    public boolean isEmpty() {
      return views.isEmpty();
    }
  
    @Override
    public <T> boolean contains(PCollectionView<T> view) {
      return views.contains(view);
    }
  }
  