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.web;
  
  import com.google.common.collect.ImmutableSet;
  import java.util.Optional;
  import java.util.Set;
  import org.openqa.selenium.internal.Require;
  
  public class MergedResource implements Resource {
  
    private final Resource base;
    private final Optional<Resource> next;
  
    public MergedResource(Resource base) {
      this(base, null);
    }
  
    private MergedResource(Resource base, Resource next) {
      this.base = Require.nonNull("Base resource", base);
      this.next = Optional.ofNullable(next);
    }
  
    public MergedResource alsoCheck(Resource resource) {
      return new MergedResource(this, Require.nonNull("Resource", resource));
    }
  
    @Override
    public String name() {
      return base.name();
    }
  
    @Override
    public Optional<Resource> get(String path) {
      Optional<Resource> resource = base.get(path);
      if (resource.isPresent()) {
        return resource;
      }
  
      if (!next.isPresent()) {
        return Optional.empty();
      }
  
      return next.get().get(path);
    }
  
    @Override
    public boolean isDirectory() {
      return base.isDirectory() || next.map(Resource::isDirectory).orElse(false);
    }
  
    @Override
    public Set<Resource> list() {
      ImmutableSet.Builder<Resource> resources = ImmutableSet.builder();
      resources.addAll(base.list());
      next.ifPresent(res -> resources.addAll(res.list()));
      return resources.build();
    }
  
    @Override
    public Optional<byte[]> read() {
      Optional<byte[]> data = base.read();
      if (data.isPresent()) {
        return data;
      }
  
      if (!next.isPresent()) {
        return Optional.empty();
      }
  
      return next.get().read();
    }
  }
  