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.twister2.translators.functions;
  
  import edu.iu.dsc.tws.api.tset.fn.SourceFunc;
  import org.apache.beam.sdk.values.WindowedValue;
  import org.apache.beam.sdk.values.WindowedValues;
  
  /** A {@link SourceFunc} which executes the impulse transform contract. */
  public class ImpulseSource implements SourceFunc<WindowedValue<byte[]>> {
    private static final WindowedValue<byte[]> IMPULSE_VALUE =
        WindowedValues.valueInGlobalWindow(new byte[0]);
  
    private boolean impulseEmitted = false;
  
    @Override
    public boolean hasNext() {
      return !impulseEmitted;
    }
  
    @Override
    public WindowedValue<byte[]> next() {
      if (impulseEmitted) {
        throw new IllegalStateException("Impulse has already emitted an element.");
      }
      impulseEmitted = true;
      return IMPULSE_VALUE;
    }
  }
  