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.util;
  
  import java.lang.invoke.MethodHandles;
  import java.lang.reflect.Constructor;
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;
  import java.lang.reflect.Proxy;
  
  import static java.util.Objects.requireNonNull;
  
  /** Compatibility layer.
   *
   * <p>Allows to use advanced functionality if the latest JDK or Guava version
   * is present.
   */
  public interface Compatible {
    Compatible INSTANCE = new Factory().create();
  
    /** Same as {@code MethodHandles#privateLookupIn()}.
     * (On JDK 8, only {@link MethodHandles#lookup()} is available. */
    <T> MethodHandles.Lookup lookupPrivate(Class<T> clazz);
  
    /** Creates the implementation of Compatible suitable for the
     * current environment. */
    class Factory {
      Compatible create() {
        return (Compatible) Proxy.newProxyInstance(
            Compatible.class.getClassLoader(),
            new Class<?>[] {Compatible.class}, (proxy, method, args) -> {
              if (method.getName().equals("lookupPrivate")) {
                // Use MethodHandles.privateLookupIn if it is available (JDK 9
                // and above)
                @SuppressWarnings("rawtypes")
                final Class<?> clazz = (Class) requireNonNull(args[0], "args[0]");
                try {
                  final Method privateLookupMethod =
                      MethodHandles.class.getMethod("privateLookupIn",
                          Class.class, MethodHandles.Lookup.class);
                  final MethodHandles.Lookup lookup = MethodHandles.lookup();
                  return privateLookupMethod.invoke(null, clazz, lookup);
                } catch (NoSuchMethodException e) {
                  return privateLookupJdk8(clazz);
                }
              }
              return null;
            });
      }
  
      /** Emulates MethodHandles.privateLookupIn on JDK 8;
       * in later JDK versions, throws. */
      @SuppressWarnings("deprecation")
      static <T> MethodHandles.Lookup privateLookupJdk8(Class<T> clazz) {
        try {
          final Constructor<MethodHandles.Lookup> constructor =
              MethodHandles.Lookup.class.getDeclaredConstructor(Class.class,
                  int.class);
          if (!constructor.isAccessible()) {
            constructor.setAccessible(true);
          }
          return constructor.newInstance(clazz, MethodHandles.Lookup.PRIVATE);
        } catch (InstantiationException | IllegalAccessException
            | InvocationTargetException | NoSuchMethodException e) {
          throw new RuntimeException(e);
        }
      }
    }
  }
  