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.extensions.sql.impl.udaf;
  
  import java.util.ArrayList;
  import java.util.List;
  import org.apache.beam.sdk.transforms.Combine;
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  public class ArrayAgg {
  
    public static class ArrayAggArray<T> extends Combine.CombineFn<T, List<T>, @Nullable List<T>> {
      @Override
      public List<T> createAccumulator() {
        return new ArrayList<>();
      }
  
      @Override
      public List<T> addInput(List<T> accum, T input) {
        accum.add(input);
        return accum;
      }
  
      @Override
      public List<T> mergeAccumulators(Iterable<List<T>> accums) {
        List<T> merged = new ArrayList<>();
        for (List<T> accum : accums) {
          for (T o : accum) {
            merged.add(o);
          }
        }
        return merged;
      }
  
      @Override
      public @Nullable List<T> extractOutput(List<T> accumulator) {
        if (accumulator.isEmpty()) {
          return null;
        }
        return accumulator;
      }
    }
  }
  