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.calcite.rel.metadata;
  
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.util.Util;
  
  import com.google.common.collect.ImmutableList;
  import com.google.common.collect.ImmutableMultimap;
  import com.google.common.collect.Multimap;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.lang.reflect.InvocationHandler;
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;
  import java.lang.reflect.Proxy;
  import java.util.ArrayList;
  import java.util.List;
  
  /**
   * Implementation of the {@link RelMetadataProvider}
   * interface via the
   * {@link org.apache.calcite.util.Glossary#CHAIN_OF_RESPONSIBILITY_PATTERN}.
   *
   * <p>When a consumer calls the {@link #apply} method to ask for a provider
   * for a particular type of {@link RelNode} and {@link Metadata}, scans the list
   * of underlying providers.
   */
  public class ChainedRelMetadataProvider implements RelMetadataProvider {
    //~ Instance fields --------------------------------------------------------
  
    private final ImmutableList<RelMetadataProvider> providers;
  
    //~ Constructors -----------------------------------------------------------
  
    /**
     * Creates a chain.
     */
    @SuppressWarnings("argument.type.incompatible")
    protected ChainedRelMetadataProvider(
        ImmutableList<RelMetadataProvider> providers) {
      this.providers = providers;
      assert !providers.contains(this);
    }
  
    //~ Methods ----------------------------------------------------------------
  
    @Override public boolean equals(@Nullable Object obj) {
      return obj == this
          || obj instanceof ChainedRelMetadataProvider
          && providers.equals(((ChainedRelMetadataProvider) obj).providers);
    }
  
    @Override public int hashCode() {
      return providers.hashCode();
    }
  
    @Deprecated // to be removed before 2.0
    @Override public <@Nullable M extends @Nullable Metadata> @Nullable UnboundMetadata<M> apply(
        Class<? extends RelNode> relClass,
        final Class<? extends M> metadataClass) {
      final List<UnboundMetadata<M>> functions = new ArrayList<>();
      for (RelMetadataProvider provider : providers) {
        final UnboundMetadata<M> function =
            provider.apply(relClass, metadataClass);
        if (function == null) {
          continue;
        }
        functions.add(function);
      }
      switch (functions.size()) {
      case 0:
        return null;
      case 1:
        return functions.get(0);
      default:
        return (rel, mq) -> {
          final List<Metadata> metadataList = new ArrayList<>();
          for (UnboundMetadata<M> function : functions) {
            final Metadata metadata = function.bind(rel, mq);
            if (metadata != null) {
              metadataList.add(metadata);
            }
          }
          return metadataClass.cast(
              Proxy.newProxyInstance(metadataClass.getClassLoader(),
                  new Class[]{metadataClass},
                  new ChainedInvocationHandler(metadataList)));
        };
      }
    }
  
    @Deprecated // to be removed before 2.0
    @Override public <M extends Metadata> Multimap<Method, MetadataHandler<M>> handlers(
        MetadataDef<M> def) {
      final ImmutableMultimap.Builder<Method, MetadataHandler<M>> builder =
          ImmutableMultimap.builder();
      for (RelMetadataProvider provider : providers.reverse()) {
        builder.putAll(provider.handlers(def));
      }
      return builder.build();
    }
  
    @Override public List<MetadataHandler<?>> handlers(
        Class<? extends MetadataHandler<?>> handlerClass) {
      final ImmutableList.Builder<MetadataHandler<?>> builder =
          ImmutableList.builder();
      for (RelMetadataProvider provider : providers) {
        builder.addAll(provider.handlers(handlerClass));
      }
      return builder.build();
    }
  
    /** Creates a chain. */
    public static RelMetadataProvider of(List<RelMetadataProvider> list) {
      return new ChainedRelMetadataProvider(ImmutableList.copyOf(list));
    }
  
    /** Invocation handler that calls a list of {@link Metadata} objects,
     * returning the first non-null value. */
    private static class ChainedInvocationHandler implements InvocationHandler {
      private final List<Metadata> metadataList;
  
      ChainedInvocationHandler(List<Metadata> metadataList) {
        this.metadataList = ImmutableList.copyOf(metadataList);
      }
  
      @Override public @Nullable Object invoke(Object proxy, Method method, @Nullable Object[] args)
          throws Throwable {
        for (Metadata metadata : metadataList) {
          try {
            final Object o = method.invoke(metadata, args);
            if (o != null) {
              return o;
            }
          } catch (InvocationTargetException e) {
            throw Util.throwAsRuntime(Util.causeOrSelf(e));
          }
        }
        return null;
      }
    }
  }
  