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.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.Set;
  import java.util.stream.Collectors;
  import java.util.stream.Stream;
  
  /**
   * This creats a {@code Lookup} object from an ordered sequence of {@code Lookup} objects.
   *
   * <p>The lookup is done from left to right. The first match is returned
   * if a name can be found in two or more lookups.
   *
   * @param <T> Element type
   */
  class ConcatLookup<T> implements Lookup<T> {
    private final Lookup<T>[] lookups;
  
    ConcatLookup(Lookup<T>[] lookups) {
      this.lookups = lookups;
    }
  
    @Override public @Nullable T get(String name) {
      for (Lookup<T> lookup : lookups) {
        T t = lookup.get(name);
        if (t != null) {
          return t;
        }
      }
      return null;
    }
  
    @Override public @Nullable Named<T> getIgnoreCase(String name) {
      for (Lookup<T> lookup : lookups) {
        Named<T> t = lookup.getIgnoreCase(name);
        if (t != null) {
          return t;
        }
      }
      return null;
    }
  
    @Override public Set<String> getNames(LikePattern pattern) {
      return Stream.of(lookups)
          .flatMap(lookup -> lookup.getNames(pattern).stream())
          .collect(Collectors.toSet());
    }
  }
  