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.transforms.windowing;
  
  import java.util.Arrays;
  import java.util.Collection;
  import org.joda.time.Instant;
  
  /**
   * A {@link WindowFn} that places each value into exactly one window based on its timestamp and
   * never merges windows.
   *
   * @param <T> type of elements being windowed
   * @param <W> window type
   */
  public abstract class PartitioningWindowFn<T, W extends BoundedWindow>
      extends NonMergingWindowFn<T, W> {
    /** Returns the single window to which elements with this timestamp belong. */
    public abstract W assignWindow(Instant timestamp);
  
    @Override
    public final Collection<W> assignWindows(AssignContext c) {
      return Arrays.asList(assignWindow(c.timestamp()));
    }
  
    @Override
    public WindowMappingFn<W> getDefaultWindowMappingFn() {
      return new WindowMappingFn<W>() {
        @Override
        public W getSideInputWindow(BoundedWindow mainWindow) {
          if (mainWindow instanceof GlobalWindow) {
            throw new IllegalArgumentException(
                "Attempted to get side input window for GlobalWindow from non-global WindowFn");
          }
          return assignWindow(mainWindow.maxTimestamp());
        }
      };
    }
  
    @Override
    public final boolean assignsToOneWindow() {
      return true;
    }
  }
  