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 java.io.Serializable;
  import java.lang.reflect.Type;
  import java.lang.reflect.TypeVariable;
  import org.apache.beam.sdk.annotations.Internal;
  import org.apache.beam.sdk.coders.CannotProvideCoderException;
  import org.apache.beam.sdk.coders.Coder;
  import org.apache.beam.sdk.coders.CoderRegistry;
  import org.apache.beam.sdk.transforms.Combine.CombineFn;
  import org.apache.beam.sdk.transforms.CombineWithContext.CombineFnWithContext;
  import org.apache.beam.sdk.transforms.display.DisplayData;
  import org.apache.beam.sdk.transforms.display.HasDisplayData;
  import org.apache.beam.sdk.values.TypeDescriptor;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.ImmutableMap;
  
  /**
   * <b><i>For internal use only; no backwards-compatibility guarantees.</i></b>
   *
   * <p>This class contains the shared interfaces and abstract classes for different types of combine
   * functions.
   *
   * <p>Users should not implement or extend them directly.
   */
  @Internal
  public class CombineFnBase {
    /**
     * <b><i>For internal use only; no backwards-compatibility guarantees.</i></b>
     *
     * <p>A {@code GloballyCombineFn<InputT, AccumT, OutputT>} specifies how to combine a collection
     * of input values of type {@code InputT} into a single output value of type {@code OutputT}. It
     * does this via one or more intermediate mutable accumulator values of type {@code AccumT}.
     *
     * <p>Do not implement this interface directly. Extends {@link CombineFn} and {@link
     * CombineFnWithContext} instead.
     *
     * @param <InputT> type of input values
     * @param <AccumT> type of mutable accumulator values
     * @param <OutputT> type of output values
     */
    @Internal
    public interface GlobalCombineFn<InputT, AccumT, OutputT> extends Serializable, HasDisplayData {
  
      /**
       * Returns the {@code Coder} to use for accumulator {@code AccumT} values, or null if it is not
       * able to be inferred.
       *
       * <p>By default, uses the knowledge of the {@code Coder} being used for {@code InputT} values
       * and the enclosing {@code Pipeline}'s {@code CoderRegistry} to try to infer the Coder for
       * {@code AccumT} values.
       *
       * <p>This is the Coder used to send data through a communication-intensive shuffle step, so a
       * compact and efficient representation may have significant performance benefits.
       */
      Coder<AccumT> getAccumulatorCoder(CoderRegistry registry, Coder<InputT> inputCoder)
          throws CannotProvideCoderException;
  
      /**
       * Returns the {@code Coder} to use by default for output {@code OutputT} values, or null if it
       * is not able to be inferred.
       *
       * <p>By default, uses the knowledge of the {@code Coder} being used for input {@code InputT}
       * values and the enclosing {@code Pipeline}'s {@code CoderRegistry} to try to infer the Coder
       * for {@code OutputT} values.
       */
      Coder<OutputT> getDefaultOutputCoder(CoderRegistry registry, Coder<InputT> inputCoder)
          throws CannotProvideCoderException;
  
      /** Returns the error message for not supported default values in Combine.globally(). */
      String getIncompatibleGlobalWindowErrorMessage();
  
      /** Returns the default value when there are no values added to the accumulator. */
      OutputT defaultValue();
    }
  
    /**
     * <b><i>For internal use only; no backwards-compatibility guarantees.</i></b>
     *
     * <p>An abstract {@link GlobalCombineFn} base class shared by {@link CombineFn} and {@link
     * CombineFnWithContext}.
     *
     * <p>Do not extend this class directly. Extends {@link CombineFn} and {@link
     * CombineFnWithContext} instead.
     *
     * @param <InputT> type of input values
     * @param <AccumT> type of mutable accumulator values
     * @param <OutputT> type of output values
     */
    @Internal
    abstract static class AbstractGlobalCombineFn<InputT, AccumT, OutputT>
        implements GlobalCombineFn<InputT, AccumT, OutputT>, Serializable {
      private static final String INCOMPATIBLE_GLOBAL_WINDOW_ERROR_MESSAGE =
          "Default values are not supported in Combine.globally() if the input "
              + "PCollection is not windowed by GlobalWindows. Instead, use "
              + "Combine.globally().withoutDefaults() to output an empty PCollection if the input "
              + "PCollection is empty, or Combine.globally().asSingletonView() to get the default "
              + "output of the CombineFn if the input PCollection is empty.";
  
      @Override
      public Coder<AccumT> getAccumulatorCoder(CoderRegistry registry, Coder<InputT> inputCoder)
          throws CannotProvideCoderException {
        return registry.getCoder(
            getClass(),
            AbstractGlobalCombineFn.class,
            ImmutableMap.<Type, Coder<?>>of(getInputTVariable(), inputCoder),
            getAccumTVariable());
      }
  
      @Override
      public Coder<OutputT> getDefaultOutputCoder(CoderRegistry registry, Coder<InputT> inputCoder)
          throws CannotProvideCoderException {
        return registry.getCoder(
            getClass(),
            AbstractGlobalCombineFn.class,
            ImmutableMap.<Type, Coder<?>>of(
                getInputTVariable(),
                inputCoder,
                getAccumTVariable(),
                this.getAccumulatorCoder(registry, inputCoder)),
            getOutputTVariable());
      }
  
      @Override
      public String getIncompatibleGlobalWindowErrorMessage() {
        return INCOMPATIBLE_GLOBAL_WINDOW_ERROR_MESSAGE;
      }
  
      /** Returns the {@link TypeVariable} of {@code InputT}. */
      public TypeVariable<?> getInputTVariable() {
        return (TypeVariable<?>)
            new TypeDescriptor<InputT>(AbstractGlobalCombineFn.class) {}.getType();
      }
  
      /** Returns the {@link TypeVariable} of {@code AccumT}. */
      public TypeVariable<?> getAccumTVariable() {
        return (TypeVariable<?>)
            new TypeDescriptor<AccumT>(AbstractGlobalCombineFn.class) {}.getType();
      }
  
      /** Returns the {@link TypeVariable} of {@code OutputT}. */
      public TypeVariable<?> getOutputTVariable() {
        return (TypeVariable<?>)
            new TypeDescriptor<OutputT>(AbstractGlobalCombineFn.class) {}.getType();
      }
  
      /**
       * {@inheritDoc}
       *
       * <p>By default, does not register any display data. Implementors may override this method to
       * provide their own display data.
       */
      @Override
      public void populateDisplayData(DisplayData.Builder builder) {}
    }
  }
  