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.learning.katas.coretransforms.combine.combinefn;
  
  // beam-playground:
  //   name: CombineFn
  //   description: Task from katas averaging.
  //   multifile: false
  //   context_line: 48
  //   categories:
  //     - Combiners
  //     - Core Transforms
  //   complexity: BASIC
  //   tags:
  //     - count
  //     - transforms
  //     - numbers
  
  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;
  
  public class Task {
  
    public static void main(String[] args) {
      PipelineOptions options = PipelineOptionsFactory.fromArgs(args).create();
      Pipeline pipeline = Pipeline.create(options);
  
      PCollection<Integer> numbers = pipeline.apply(Create.of(10, 20, 50, 70, 90));
  
      PCollection<Double> output = applyTransform(numbers);
  
      output.apply(Log.ofElements());
  
      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;
      }
  
    }
  
  }