content: /**
   * Licensed 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.aurora.scheduler.http.api.security;
  
  import java.util.Optional;
  
  import com.google.common.base.Function;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * Function for retrieving an optional field from a thrift struct with runtime type-information.
   *
   * @param <T> the container struct
   * @param <V> a field that can be contained within T
   */
  interface FieldGetter<T, V> extends Function<T, Optional<V>> {
    /**
     * The type of the container struct.
     */
    Class<T> getStructClass();
  
    /**
     * The type of the optionally-contained struct.
     */
    Class<V> getValueClass();
  
    abstract class AbstractFieldGetter<T, V> implements FieldGetter<T, V> {
      private final Class<T> structClass;
      private final Class<V> valueClass;
  
      protected AbstractFieldGetter(Class<T> structClass, Class<V> valueClass) {
        this.structClass = requireNonNull(structClass);
        this.valueClass = requireNonNull(valueClass);
      }
  
      @Override
      public final Class<T> getStructClass() {
        return structClass;
      }
  
      @Override
      public final Class<V> getValueClass() {
        return valueClass;
      }
    }
  
    /**
     * Special case of field getter that can get itself.
     *
     * @param <T> The input and ouput type.
     */
    class IdentityFieldGetter<T> extends AbstractFieldGetter<T, T> {
      IdentityFieldGetter(Class<T> structClass) {
        super(structClass, structClass);
      }
  
      @Override
      public Optional<T> apply(T input) {
        return Optional.ofNullable(input);
      }
    }
  }
  