code: // Licensed to the Software Freedom Conservancy (SFC) under one
  // or more contributor license agreements.  See the NOTICE file
  // distributed with this work for additional information
  // regarding copyright ownership.  The SFC 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.openqa.selenium.grid.config;
  
  import static com.google.common.collect.ImmutableSortedSet.toImmutableSortedSet;
  import static java.util.Comparator.naturalOrder;
  
  import com.google.common.collect.ImmutableList;
  import java.util.List;
  import java.util.Locale;
  import java.util.Optional;
  import java.util.Set;
  import org.openqa.selenium.internal.Require;
  
  /**
   * Exposes environment variables as config settings by mapping "section.option" to "SECTION_OPTION".
   * Dashes and periods in the options are converted to underscores, and all characters are
   * upper-cased assuming a US English locale.
   */
  public class EnvConfig implements Config {
  
    @Override
    public Optional<List<String>> getAll(String section, String option) {
      Require.nonNull("Section name", section);
      Require.nonNull("Option name", option);
  
      String key =
          String.format("%s_%s", section, option)
              .toUpperCase(Locale.ENGLISH)
              .replace("-", "_")
              .replace(".", "_");
  
      String value = System.getenv().get(key);
      if (value == null) {
        return Optional.empty();
      }
  
      if (value.startsWith("$")) {
        value = System.getenv(value.substring(1));
      }
  
      return Optional.ofNullable(value).map(ImmutableList::of);
    }
  
    @Override
    public Set<String> getSectionNames() {
      return System.getenv().keySet().stream()
          // We need at least two "_" characters
          .filter(key -> key.split("_").length > 1)
          .map(key -> key.substring(0, key.indexOf('_')))
          .map(key -> key.toLowerCase(Locale.ENGLISH))
          .collect(toImmutableSortedSet(naturalOrder()));
    }
  
    @Override
    public Set<String> getOptions(String section) {
      Require.nonNull("Section name to get options for", section);
  
      String prefix = String.format("%s_", section).toUpperCase(Locale.ENGLISH);
      return System.getenv().keySet().stream()
          .filter(key -> key.startsWith(prefix))
          .map(key -> key.substring(prefix.length()))
          .map(key -> key.toLowerCase(Locale.ENGLISH))
          .collect(toImmutableSortedSet(naturalOrder()));
    }
  }
  