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   * 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.flink.translation.functions;
  
  import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
  import org.apache.beam.sdk.transforms.windowing.WindowFn;
  import org.apache.beam.sdk.values.WindowedValue;
  import org.apache.beam.sdk.values.WindowedValues;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Iterables;
  import org.joda.time.Instant;
  
  /** {@link org.apache.beam.sdk.transforms.windowing.WindowFn.AssignContext} for Flink functions. */
  @SuppressWarnings({"keyfor", "nullness"}) // TODO(https://github.com/apache/beam/issues/20497)
  class FlinkAssignContext<InputT, W extends BoundedWindow>
      extends WindowFn<InputT, W>.AssignContext {
    private final WindowedValue<InputT> value;
  
    FlinkAssignContext(WindowFn<InputT, W> fn, WindowedValue<InputT> value) {
      fn.super();
      if (Iterables.size(value.getWindows()) != 1) {
        throw new IllegalArgumentException(
            String.format(
                "%s passed to window assignment must be in a single window, but it was in %s: %s",
                WindowedValues.class.getSimpleName(),
                Iterables.size(value.getWindows()),
                value.getWindows()));
      }
      this.value = value;
    }
  
    @Override
    public InputT element() {
      return value.getValue();
    }
  
    @Override
    public Instant timestamp() {
      return value.getTimestamp();
    }
  
    @Override
    public BoundedWindow window() {
      return Iterables.getOnlyElement(value.getWindows());
    }
  }
  