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 org.apache.calcite.util.LazyReference;
  import org.apache.calcite.util.NameMap;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.Set;
  
  /**
   * This class can be used to make a snapshot of a lookups.
   *
   * @param <T> Element Type
   */
  public class SnapshotLookup<T> implements Lookup<T> {
  
    private final Lookup<T> delegate;
    private LazyReference<Lookup<T>> cachedDelegate = new LazyReference<>();
    private boolean enabled = true;
  
    public SnapshotLookup(Lookup<T> delegate) {
      this.delegate = delegate;
    }
  
    @Override public @Nullable T get(final String name) {
      return delegate().get(name);
    }
  
    @Override public @Nullable Named<T> getIgnoreCase(final String name) {
      return delegate().getIgnoreCase(name);
    }
  
    @Override public Set<String> getNames(final LikePattern pattern) {
      return delegate().getNames(pattern);
    }
  
    private Lookup<T> delegate() {
      if (!enabled) {
        return delegate;
      }
      return cachedDelegate.getOrCompute(() -> new NameMapLookup<>(loadNameMap()));
    }
  
    private NameMap<T> loadNameMap() {
      NameMap<T> map = new NameMap<>();
      for (String name : delegate.getNames(LikePattern.any())) {
        T entry = delegate.get(name);
        if (entry != null) {
          map.put(name, entry);
        }
      }
      return map;
    }
  
    public void enable(boolean enabled) {
      if (!enabled) {
        cachedDelegate.reset();
      }
      this.enabled = enabled;
    }
  
  }
  