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;
  
  import java.util.Collections;
  import java.util.Map;
  import java.util.Set;
  import java.util.function.Function;
  import java.util.stream.Collector;
  import java.util.stream.Collectors;
  import java.util.stream.Stream;
  import org.openqa.selenium.internal.Require;
  
  public class PersistentCapabilities implements Capabilities {
  
    private final ImmutableCapabilities caps;
    private final ImmutableCapabilities overrides;
    private final int hashCode;
  
    public PersistentCapabilities() {
      this(new ImmutableCapabilities());
    }
  
    public PersistentCapabilities(Capabilities source) {
      this(source, new ImmutableCapabilities());
    }
  
    private PersistentCapabilities(Capabilities previousValues, Capabilities newValues) {
      Require.nonNull("Source capabilities", previousValues, "may be empty, but must be set.");
      Require.nonNull("Additional capabilities", newValues, "may be empty, but must be set.");
      this.caps = ImmutableCapabilities.copyOf(previousValues);
      this.overrides = ImmutableCapabilities.copyOf(newValues);
      this.hashCode = SharedCapabilitiesMethods.hashCode(this);
    }
  
    public PersistentCapabilities setCapability(String name, Object value) {
      Require.nonNull("Name", name);
      Require.nonNull("Value", value);
  
      return new PersistentCapabilities(this, new ImmutableCapabilities(name, value));
    }
  
    @Override
    public Map<String, Object> asMap() {
      return getCapabilityNames().stream()
          .collect(toUnmodifiableMap(Function.identity(), this::getCapability));
    }
  
    @Override
    public Object getCapability(String capabilityName) {
      Require.nonNull("Capability name", capabilityName);
      Object capability = overrides.getCapability(capabilityName);
      if (capability != null) {
        return capability;
      }
      return caps.getCapability(capabilityName);
    }
  
    @Override
    public Capabilities merge(Capabilities other) {
      Require.nonNull("Other capabilities", other, "may be empty, but must be set.");
      return new PersistentCapabilities(this, other);
    }
  
    @Override
    public Set<String> getCapabilityNames() {
      return Stream.concat(
              caps.getCapabilityNames().stream(), overrides.getCapabilityNames().stream())
          .collect(toUnmodifiableSet());
    }
  
    // Needed, since we're dependent on Java 8 as a minimum version
    private <T, K, U> Collector<T, ?, Map<K, U>> toUnmodifiableMap(
        Function<? super T, ? extends K> keyMapper, Function<? super T, ? extends U> valueMapper) {
      return Collectors.collectingAndThen(
          Collectors.toMap(keyMapper, valueMapper), Collections::unmodifiableMap);
    }
  
    // Needed, since we're dependent on Java 8 as a minimum version
    private <T> Collector<T, ?, Set<T>> toUnmodifiableSet() {
      return Collectors.collectingAndThen(Collectors.toSet(), Collections::unmodifiableSet);
    }
  
    @Override
    public String toString() {
      return SharedCapabilitiesMethods.toString(this);
    }
  
    @Override
    public int hashCode() {
      return hashCode;
    }
  
    @Override
    public boolean equals(Object o) {
      if (!(o instanceof Capabilities)) {
        return false;
      }
      return SharedCapabilitiesMethods.equals(this, (Capabilities) o);
    }
  }
  