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.Pair;
  import org.apache.calcite.util.Util;
  
  import com.google.common.cache.CacheBuilder;
  import com.google.common.cache.CacheLoader;
  import com.google.common.cache.LoadingCache;
  import com.google.common.util.concurrent.UncheckedExecutionException;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.concurrent.ExecutionException;
  
  /**
   * Implementation of {@link MetadataFactory} that gets providers from a
   * {@link RelMetadataProvider} and stores them in a cache.
   *
   * <p>The cache does not store metadata. It remembers which providers can
   * provide which kinds of metadata, for which kinds of relational
   * expressions.
   *
   * @deprecated Use {@link RelMetadataQuery}.
   */
  @Deprecated // to be removed before 2.0
  public class MetadataFactoryImpl implements MetadataFactory {
    @SuppressWarnings("unchecked")
    public static final UnboundMetadata<@Nullable Metadata> DUMMY = (rel, mq) -> null;
  
    private final LoadingCache<
        Pair<Class<RelNode>, Class<Metadata>>,
        UnboundMetadata<@Nullable Metadata>> cache;
  
    public MetadataFactoryImpl(RelMetadataProvider provider) {
      this.cache = CacheBuilder.newBuilder().build(loader(provider));
    }
  
    private static CacheLoader<Pair<Class<RelNode>, Class<Metadata>>,
        UnboundMetadata<@Nullable Metadata>> loader(final RelMetadataProvider provider) {
      //noinspection RedundantTypeArguments
      return CacheLoader.<Pair<Class<RelNode>, Class<Metadata>>,
          UnboundMetadata<@Nullable Metadata>>from(key -> {
            final UnboundMetadata<@Nullable Metadata> function =
                provider.apply(key.left, key.right);
            // Return DUMMY, not null, so the cache knows to not ask again.
            return function != null ? function : DUMMY;
          });
    }
  
    @Override public <@Nullable M extends @Nullable Metadata> M query(
        RelNode rel, RelMetadataQuery mq,
        Class<M> metadataClazz) {
      try {
        //noinspection unchecked
        final Pair<Class<RelNode>, Class<Metadata>> key =
            Pair.of((Class<RelNode>) rel.getClass(), (Class<Metadata>) metadataClazz);
        final Metadata apply = cache.get(key).bind(rel, mq);
        return metadataClazz.cast(apply);
      } catch (UncheckedExecutionException | ExecutionException e) {
        throw Util.throwAsRuntime(Util.causeOrSelf(e));
      }
    }
  }
  