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.
   */
  
  // beam-playground:
  //   name: combine-fn
  //   description: Combine-fn example.
  //   multifile: false
  //   context_line: 49
  //   categories:
  //     - Quickstart
  //   complexity: ADVANCED
  //   tags:
  //     - hellobeam
  
  import java.io.Serializable;
  import java.util.Objects;
  import org.apache.beam.learning.katas.util.Log;
  import org.apache.beam.sdk.Pipeline;
  import org.apache.beam.sdk.options.PipelineOptions;
  import org.apache.beam.sdk.options.PipelineOptionsFactory;
  import org.apache.beam.sdk.transforms.Combine;
  import org.apache.beam.sdk.transforms.Combine.CombineFn;
  import org.apache.beam.sdk.transforms.Create;
  import org.apache.beam.sdk.values.PCollection;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  import org.apache.beam.sdk.transforms.DoFn;
  import org.apache.beam.sdk.transforms.ParDo;
  
  public class Task {
  
      private static final Logger LOG = LoggerFactory.getLogger(Task.class);
  
      public static void main(String[] args) {
          PipelineOptions options = PipelineOptionsFactory.fromArgs(args).create();
          Pipeline pipeline = Pipeline.create(options);
  
          PCollection<Integer> input = pipeline.apply(Create.of(10, 20, 50, 70, 90));
  
          PCollection<Double> output = applyTransform(input);
  
          output.apply(ParDo.of(new LogOutput<>()));
  
          pipeline.run();
      }
  
      static PCollection<Double> applyTransform(PCollection<Integer> input) {
          return input.apply(Combine.globally(new AverageFn()));
      }
  
      static class AverageFn extends CombineFn<Integer, AverageFn.Accum, Double> {
  
          class Accum implements Serializable {
              int sum = 0;
              int count = 0;
  
              @Override
              public boolean equals(Object o) {
                  if (this == o) {
                      return true;
                  }
                  if (o == null || getClass() != o.getClass()) {
                      return false;
                  }
                  Accum accum = (Accum) o;
                  return sum == accum.sum &&
                          count == accum.count;
              }
  
              @Override
              public int hashCode() {
                  return Objects.hash(sum, count);
              }
          }
  
          @Override
          public Accum createAccumulator() {
              return new Accum();
          }
  
          @Override
          public Accum addInput(Accum accumulator, Integer input) {
              accumulator.sum += input;
              accumulator.count++;
  
              return accumulator;
          }
  
          @Override
          public Accum mergeAccumulators(Iterable<Accum> accumulators) {
              Accum merged = createAccumulator();
  
              for (Accum accumulator : accumulators) {
                  merged.sum += accumulator.sum;
                  merged.count += accumulator.count;
              }
  
              return merged;
          }
  
          @Override
          public Double extractOutput(Accum accumulator) {
              return ((double) accumulator.sum) / accumulator.count;
          }
  
      }
  
      static class LogOutput<T> extends DoFn<T, T> {
          private String prefix;
  
          LogOutput() {
              this.prefix = "Processing element";
          }
  
          LogOutput(String prefix) {
              this.prefix = prefix;
          }
  
          @ProcessElement
          public void processElement(ProcessContext c) throws Exception {
              LOG.info(prefix + ": {}", c.element());
          }
      }
  
  }