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.sdk.state;
  
  import org.apache.beam.sdk.annotations.Internal;
  import org.apache.beam.sdk.options.PipelineOptions;
  import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
  import org.apache.beam.sdk.values.PCollectionView;
  
  /** <b><i>For internal use only; no backwards-compatibility guarantees.</i></b> */
  @Internal
  public class StateContexts {
    private static final StateContext<BoundedWindow> NULL_CONTEXT =
        new StateContext<BoundedWindow>() {
          @Override
          public PipelineOptions getPipelineOptions() {
            throw new IllegalArgumentException("cannot call getPipelineOptions() in a null context");
          }
  
          @Override
          public <T> T sideInput(PCollectionView<T> view) {
            throw new IllegalArgumentException("cannot call sideInput() in a null context");
          }
  
          @Override
          public BoundedWindow window() {
            throw new IllegalArgumentException("cannot call window() in a null context");
          }
        };
  
    /** Returns a fake {@link StateContext}. */
    @SuppressWarnings("unchecked")
    public static <W extends BoundedWindow> StateContext<W> nullContext() {
      return (StateContext<W>) NULL_CONTEXT;
    }
  
    public static <W extends BoundedWindow> StateContext<W> windowOnlyContext(W window) {
      return new WindowOnlyContext<>(window);
    }
  
    private static class WindowOnlyContext<W extends BoundedWindow> implements StateContext<W> {
      private final W window;
  
      private WindowOnlyContext(W window) {
        this.window = window;
      }
  
      @Override
      public PipelineOptions getPipelineOptions() {
        throw new IllegalArgumentException(
            "cannot call getPipelineOptions() in a window-only context");
      }
  
      @Override
      public <T> T sideInput(PCollectionView<T> view) {
        throw new IllegalArgumentException("cannot call sideInput() in a window-only context");
      }
  
      @Override
      public W window() {
        return window;
      }
    }
  }
  