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.schema.lookup;
  
  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.time.Duration;
  import java.util.Set;
  import java.util.concurrent.ExecutionException;
  import java.util.concurrent.TimeUnit;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * This class is using a {@code LoadingCache} to speed up lookups,
   * delegated to another {@link Lookup} instance.
   *
   * <p>This class is thread safe. All entries are evicted after one minute.
   * Negative matches are never cached. If a new entry
   * becomes available in the associated {@code Lookup}, it's immediately
   * visible outside. If an entry is deleted in the associated {@code Lookup},
   * it takes one minute until it disappears if it was cached in the last minute.
   * Otherwise, it disappears immediately.
   *
   * @param <T> Element Type
   */
  public class LoadingCacheLookup<T> implements Lookup<T> {
    private final Lookup<T> delegate;
  
    private final LoadingCache<String, T> cache;
    private final LoadingCache<String, Named<T>> cacheIgnoreCase;
  
    /**
     * Creates a {@code Lookup} object with a `LoadingCache`inside.
     *
     * @param delegate The {@code Lookup} object, which should be cached
     * @param expiration The duration after which the entries are evicted from
     *                   the loading cache.
     */
    public LoadingCacheLookup(Lookup<T> delegate, Duration expiration) {
      this.delegate = delegate;
      this.cache = CacheBuilder.newBuilder()
          .expireAfterWrite(expiration.toMillis(), TimeUnit.MILLISECONDS)
          .build(CacheLoader.from(name -> requireNonNull(delegate.get(name))));
      this.cacheIgnoreCase = CacheBuilder.newBuilder()
          .expireAfterWrite(expiration.toMillis(), TimeUnit.MILLISECONDS)
          .build(CacheLoader.from(name -> requireNonNull(delegate.getIgnoreCase(name))));
    }
  
    /**
     * Creates a {@code Lookup} object with a `LoadingCache`inside.
     *
     * <p>The expiration is set to 1 minute.
     *
     * @param delegate The {@code Lookup} object, which should be cached
     */
    public LoadingCacheLookup(Lookup<T> delegate) {
      this(delegate, Duration.ofMinutes(1));
    }
  
    @Override public @Nullable T get(String name) {
      try {
        return cache.get(name);
      } catch (UncheckedExecutionException e) {
        if (e.getCause() instanceof NullPointerException) {
          return null;
        }
        throw e;
      } catch (ExecutionException e) {
        throw new RuntimeException(e);
      }
    }
  
    @Override public @Nullable Named<T> getIgnoreCase(String name) {
      try {
        return cacheIgnoreCase.get(name);
      } catch (UncheckedExecutionException e) {
        if (e.getCause() instanceof NullPointerException) {
          return null;
        }
        throw e;
      } catch (ExecutionException e) {
        throw new RuntimeException(e);
      }
    }
  
    @Override public Set<String> getNames(LikePattern pattern) {
      return delegate.getNames(pattern);
    }
  }
  