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;
  
  import java.lang.reflect.ParameterizedType;
  import java.lang.reflect.TypeVariable;
  import java.util.Optional;
  import javax.annotation.Nonnull;
  import javax.annotation.Nullable;
  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;
  import org.apache.beam.sdk.transforms.display.DisplayData;
  import org.apache.beam.sdk.util.Preconditions;
  import org.apache.beam.sdk.values.TypeDescriptor;
  
  /**
   * A {@link Combine.CombineFn} delegating all relevant calls to given delegate. This is used to
   * create a type anonymous class for cases where the CombineFn is a generic class. The anonymous
   * class can then be used in a UDAF as
   *
   * <pre>
   *   .registerUdaf("UDAF", new TypedCombineFnDelegate<>(genericCombineFn) {})
   * </pre>
   *
   * @param <InputT> the type of input
   * @param <AccumT> the type of accumulator
   * @param <OutputT> the type of output
   */
  public class TypedCombineFnDelegate<InputT, AccumT, OutputT>
      extends Combine.CombineFn<InputT, AccumT, OutputT> {
  
    private final Combine.CombineFn<InputT, AccumT, OutputT> delegate;
  
    protected TypedCombineFnDelegate(Combine.CombineFn<InputT, AccumT, OutputT> delegate) {
      this.delegate = delegate;
    }
  
    @Override
    public TypeDescriptor<OutputT> getOutputType() {
      return Optional.<TypeDescriptor<OutputT>>ofNullable(getGenericSuperTypeAtIndex(2))
          .orElse(delegate.getOutputType());
    }
  
    @Override
    public TypeDescriptor<InputT> getInputType() {
      return Optional.<TypeDescriptor<InputT>>ofNullable(getGenericSuperTypeAtIndex(0))
          .orElse(delegate.getInputType());
    }
  
    @Override
    public AccumT createAccumulator() {
      return delegate.createAccumulator();
    }
  
    @Override
    public AccumT addInput(AccumT mutableAccumulator, InputT input) {
      return delegate.addInput(mutableAccumulator, input);
    }
  
    @Override
    public AccumT mergeAccumulators(Iterable<AccumT> accumulators) {
      return delegate.mergeAccumulators(accumulators);
    }
  
    @Override
    public OutputT extractOutput(AccumT accumulator) {
      return delegate.extractOutput(accumulator);
    }
  
    @Override
    public AccumT compact(AccumT accumulator) {
      return delegate.compact(accumulator);
    }
  
    @Override
    public OutputT apply(Iterable<? extends InputT> inputs) {
      return delegate.apply(inputs);
    }
  
    @Override
    public OutputT defaultValue() {
      return delegate.defaultValue();
    }
  
    @Override
    public Coder<AccumT> getAccumulatorCoder(CoderRegistry registry, Coder<InputT> inputCoder)
        throws CannotProvideCoderException {
      return delegate.getAccumulatorCoder(registry, inputCoder);
    }
  
    @Override
    public Coder<OutputT> getDefaultOutputCoder(CoderRegistry registry, Coder<InputT> inputCoder)
        throws CannotProvideCoderException {
      return delegate.getDefaultOutputCoder(registry, inputCoder);
    }
  
    @Override
    public String getIncompatibleGlobalWindowErrorMessage() {
      return delegate.getIncompatibleGlobalWindowErrorMessage();
    }
  
    @Override
    public TypeVariable<?> getInputTVariable() {
      return delegate.getInputTVariable();
    }
  
    @Override
    public TypeVariable<?> getAccumTVariable() {
      return delegate.getAccumTVariable();
    }
  
    @Override
    public TypeVariable<?> getOutputTVariable() {
      return delegate.getOutputTVariable();
    }
  
    @Override
    public void populateDisplayData(DisplayData.Builder builder) {
      delegate.populateDisplayData(builder);
    }
  
    @SuppressWarnings("unchecked")
    @Nullable
    private <T> TypeDescriptor<T> getGenericSuperTypeAtIndex(int index) {
      Class<?> cls = Preconditions.checkArgumentNotNull(getClass());
      do {
        Class<?> superClass = cls.getSuperclass();
        if (superClass == null) {
          break;
        }
        if (superClass.equals(TypedCombineFnDelegate.class)) {
          @Nonnull
          ParameterizedType superType =
              (ParameterizedType) Preconditions.checkArgumentNotNull(cls.getGenericSuperclass());
          TypeDescriptor<T> candidate =
              (TypeDescriptor<T>) TypeDescriptor.of(superType.getActualTypeArguments()[index]);
          if (!(candidate instanceof TypeVariable)) {
            return candidate;
          }
        }
        cls = superClass;
      } while (true);
      return null;
    }
  }
  