/*
 * Copyright (C) 2012 The Guava Authors
 *
 * 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 com.google.common.reflect;

import com.google.common.annotations.Beta;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Arrays;
import org.checkerframework.checker.nullness.qual.Nullable;

Abstract implementation of InvocationHandler that handles Object.equals, Object.hashCode and Object.toString. For example: 
class Unsupported extends AbstractInvocationHandler {
  protected Object handleInvocation(Object proxy, Method method, Object[] args) {
    throw new UnsupportedOperationException();
  }
}
CharSequence unsupported = Reflection.newProxy(CharSequence.class, new Unsupported());

Author:
Ben Yu
Since:
12.0/**
 * Abstract implementation of {@link InvocationHandler} that handles {@link Object#equals}, {@link
 * Object#hashCode} and {@link Object#toString}. For example:
 *
 * <pre>
 * class Unsupported extends AbstractInvocationHandler {
 *   protected Object handleInvocation(Object proxy, Method method, Object[] args) {
 *     throw new UnsupportedOperationException();
 *   }
 * }
 *
 * CharSequence unsupported = Reflection.newProxy(CharSequence.class, new Unsupported());
 * </pre>
 *
 * @author Ben Yu
 * @since 12.0
 */
@Beta
public abstract class AbstractInvocationHandler implements InvocationHandler {

  private static final Object[] NO_ARGS = {};

  
{@inheritDoc}

  
proxy.hashCode() delegates to hashCode 
proxy.toString() delegates to toString 
proxy.equals(argument) returns true if: 

        
proxy and argument are of the same type 
and equals returns true for the InvocationHandler of argument 
  
other method calls are dispatched to handleInvocation. 
/**
   * {@inheritDoc}
   *
   * <ul>
   *   <li>{@code proxy.hashCode()} delegates to {@link AbstractInvocationHandler#hashCode}
   *   <li>{@code proxy.toString()} delegates to {@link AbstractInvocationHandler#toString}
   *   <li>{@code proxy.equals(argument)} returns true if:
   *       <ul>
   *         <li>{@code proxy} and {@code argument} are of the same type
   *         <li>and {@link AbstractInvocationHandler#equals} returns true for the {@link
   *             InvocationHandler} of {@code argument}
   *       </ul>
   *   <li>other method calls are dispatched to {@link #handleInvocation}.
   * </ul>
   */
  @Override
  public final Object invoke(Object proxy, Method method, Object @Nullable [] args)
      throws Throwable {
    if (args == null) {
      args = NO_ARGS;
    }
    if (args.length == 0 && method.getName().equals("hashCode")) {
      return hashCode();
    }
    if (args.length == 1
        && method.getName().equals("equals")
        && method.getParameterTypes()[0] == Object.class) {
      Object arg = args[0];
      if (arg == null) {
        return false;
      }
      if (proxy == arg) {
        return true;
      }
      return isProxyOfSameInterfaces(arg, proxy.getClass())
          && equals(Proxy.getInvocationHandler(arg));
    }
    if (args.length == 0 && method.getName().equals("toString")) {
      return toString();
    }
    return handleInvocation(proxy, method, args);
  }

  
invoke delegates to this method upon any method invocation on the proxy instance, except Object.equals, Object.hashCode and Object.toString. The result will be returned as the proxied method's return value. 
Unlike invoke, args will never be null. When the method has no parameter, an empty array is passed in. /**
   * {@link #invoke} delegates to this method upon any method invocation on the proxy instance,
   * except {@link Object#equals}, {@link Object#hashCode} and {@link Object#toString}. The result
   * will be returned as the proxied method's return value.
   *
   * <p>Unlike {@link #invoke}, {@code args} will never be null. When the method has no parameter,
   * an empty array is passed in.
   */
  protected abstract Object handleInvocation(Object proxy, Method method, Object[] args)
      throws Throwable;

  
By default delegates to Object.equals so instances are only equal if they are identical. proxy.equals(argument) returns true if: 

  
proxy and argument are of the same type 
and this method returns true for the InvocationHandler of argument 
Subclasses can override this method to provide custom equality.
/**
   * By default delegates to {@link Object#equals} so instances are only equal if they are
   * identical. {@code proxy.equals(argument)} returns true if:
   *
   * <ul>
   *   <li>{@code proxy} and {@code argument} are of the same type
   *   <li>and this method returns true for the {@link InvocationHandler} of {@code argument}
   * </ul>
   *
   * <p>Subclasses can override this method to provide custom equality.
   */
  @Override
  public boolean equals(Object obj) {
    return super.equals(obj);
  }

  
By default delegates to Object.hashCode. The dynamic proxies' hashCode() will delegate to this method. Subclasses can override this method to provide custom equality. /**
   * By default delegates to {@link Object#hashCode}. The dynamic proxies' {@code hashCode()} will
   * delegate to this method. Subclasses can override this method to provide custom equality.
   */
  @Override
  public int hashCode() {
    return super.hashCode();
  }

  
By default delegates to Object.toString. The dynamic proxies' toString() will delegate to this method. Subclasses can override this method to provide custom string representation for the proxies. /**
   * By default delegates to {@link Object#toString}. The dynamic proxies' {@code toString()} will
   * delegate to this method. Subclasses can override this method to provide custom string
   * representation for the proxies.
   */
  @Override
  public String toString() {
    return super.toString();
  }

  private static boolean isProxyOfSameInterfaces(Object arg, Class<?> proxyClass) {
    return proxyClass.isInstance(arg)
        // Equal proxy instances should mostly be instance of proxyClass
        // Under some edge cases (such as the proxy of JDK types serialized and then deserialized)
        // the proxy type may not be the same.
        // We first check isProxyClass() so that the common case of comparing with non-proxy objects
        // is efficient.
        || (Proxy.isProxyClass(arg.getClass())
            && Arrays.equals(arg.getClass().getInterfaces(), proxyClass.getInterfaces()));
  }
}