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;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /**
   * {@code PTransform}s for computing the sum of the elements in a {@code PCollection}, or the sum of
   * the values associated with each key in a {@code PCollection} of {@code KV}s.
   *
   * <p>Example 1: get the sum of a {@code PCollection} of {@code Double}s.
   *
   * <pre>{@code
   * PCollection<Double> input = ...;
   * PCollection<Double> sum = input.apply(Sum.doublesGlobally());
   * }</pre>
   *
   * <p>Example 2: calculate the sum of the {@code Integer}s associated with each unique key (which is
   * of type {@code String}).
   *
   * <pre>{@code
   * PCollection<KV<String, Integer>> input = ...;
   * PCollection<KV<String, Integer>> sumPerKey = input
   *     .apply(Sum.<String>integersPerKey());
   * }</pre>
   */
  public class Sum {
  
    private Sum() {
      // do not instantiate
    }
  
    /**
     * Returns a {@code PTransform} that takes an input {@code PCollection<Integer>} and returns a
     * {@code PCollection<Integer>} whose contents is the sum of the input {@code PCollection}'s
     * elements, or {@code 0} if there are no elements.
     */
    public static Combine.Globally<Integer, Integer> integersGlobally() {
      return Combine.globally(Sum.ofIntegers());
    }
  
    /**
     * Returns a {@code PTransform} that takes an input {@code PCollection<KV<K, Integer>>} and
     * returns a {@code PCollection<KV<K, Integer>>} that contains an output element mapping each
     * distinct key in the input {@code PCollection} to the sum of the values associated with that key
     * in the input {@code PCollection}.
     */
    public static <K> Combine.PerKey<K, Integer, Integer> integersPerKey() {
      return Combine.perKey(Sum.ofIntegers());
    }
  
    /**
     * Returns a {@code PTransform} that takes an input {@code PCollection<Long>} and returns a {@code
     * PCollection<Long>} whose contents is the sum of the input {@code PCollection}'s elements, or
     * {@code 0} if there are no elements.
     */
    public static Combine.Globally<Long, Long> longsGlobally() {
      return Combine.globally(Sum.ofLongs());
    }
  
    /**
     * Returns a {@code PTransform} that takes an input {@code PCollection<KV<K, Long>>} and returns a
     * {@code PCollection<KV<K, Long>>} that contains an output element mapping each distinct key in
     * the input {@code PCollection} to the sum of the values associated with that key in the input
     * {@code PCollection}.
     */
    public static <K> Combine.PerKey<K, Long, Long> longsPerKey() {
      return Combine.perKey(Sum.ofLongs());
    }
  
    /**
     * Returns a {@code PTransform} that takes an input {@code PCollection<Double>} and returns a
     * {@code PCollection<Double>} whose contents is the sum of the input {@code PCollection}'s
     * elements, or {@code 0} if there are no elements.
     */
    public static Combine.Globally<Double, Double> doublesGlobally() {
      return Combine.globally(Sum.ofDoubles());
    }
  
    /**
     * Returns a {@code PTransform} that takes an input {@code PCollection<KV<K, Double>>} and returns
     * a {@code PCollection<KV<K, Double>>} that contains an output element mapping each distinct key
     * in the input {@code PCollection} to the sum of the values associated with that key in the input
     * {@code PCollection}.
     */
    public static <K> Combine.PerKey<K, Double, Double> doublesPerKey() {
      return Combine.perKey(Sum.ofDoubles());
    }
  
    /**
     * A {@code SerializableFunction} that computes the sum of an {@code Iterable} of {@code
     * Integer}s, useful as an argument to {@link Combine#globally} or {@link Combine#perKey}.
     */
    public static Combine.BinaryCombineIntegerFn ofIntegers() {
      return new SumIntegerFn();
    }
  
    /**
     * A {@code SerializableFunction} that computes the sum of an {@code Iterable} of {@code Double}s,
     * useful as an argument to {@link Combine#globally} or {@link Combine#perKey}.
     */
    public static Combine.BinaryCombineDoubleFn ofDoubles() {
      return new SumDoubleFn();
    }
  
    /**
     * A {@code SerializableFunction} that computes the sum of an {@code Iterable} of {@code Long}s,
     * useful as an argument to {@link Combine#globally} or {@link Combine#perKey}.
     */
    public static Combine.BinaryCombineLongFn ofLongs() {
      return new SumLongFn();
    }
  
    /////////////////////////////////////////////////////////////////////////////
  
    private static class SumIntegerFn extends Combine.BinaryCombineIntegerFn {
  
      @Override
      public int apply(int a, int b) {
        return a + b;
      }
  
      @Override
      public int identity() {
        return 0;
      }
  
      @Override
      public boolean equals(@Nullable Object other) {
        return other != null && other.getClass().equals(this.getClass());
      }
  
      @Override
      public int hashCode() {
        return getClass().hashCode();
      }
    }
  
    private static class SumLongFn extends Combine.BinaryCombineLongFn {
  
      @Override
      public long apply(long a, long b) {
        return a + b;
      }
  
      @Override
      public long identity() {
        return 0;
      }
  
      @Override
      public boolean equals(@Nullable Object other) {
        return other != null && other.getClass().equals(this.getClass());
      }
  
      @Override
      public int hashCode() {
        return getClass().hashCode();
      }
    }
  
    private static class SumDoubleFn extends Combine.BinaryCombineDoubleFn {
  
      @Override
      public double apply(double a, double b) {
        return a + b;
      }
  
      @Override
      public double identity() {
        return 0;
      }
  
      @Override
      public boolean equals(@Nullable Object other) {
        return other != null && other.getClass().equals(this.getClass());
      }
  
      @Override
      public int hashCode() {
        return getClass().hashCode();
      }
    }
  }
  