/*
 * Copyright 2002-2017 the original author or 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
 *
 *      https://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.springframework.aop.support;

import java.util.Map;
import java.util.WeakHashMap;

import org.aopalliance.intercept.MethodInvocation;

import org.springframework.aop.DynamicIntroductionAdvice;
import org.springframework.aop.IntroductionInterceptor;
import org.springframework.aop.ProxyMethodInvocation;
import org.springframework.lang.Nullable;
import org.springframework.util.ReflectionUtils;

Convenient implementation of the IntroductionInterceptor interface. 
This differs from DelegatingIntroductionInterceptor in that a single instance of this class can be used to advise multiple target objects, and each target object will have its own delegate (whereas DelegatingIntroductionInterceptor
shares the same delegate, and hence the same state across all targets).
The suppressInterface method can be used to suppress interfaces implemented by the delegate class but which should not be introduced to the owning AOP proxy. 
An instance of this class is serializable if the delegates are.
Note: There are some implementation similarities between this class and DelegatingIntroductionInterceptor that suggest a possible refactoring to extract a common ancestor class in the future.
Author:
Adrian Colyer, Juergen Hoeller
See Also:
IntroductionInfoSupport.suppressInterface
DelegatingIntroductionInterceptor
Since:
2.0/**
 * Convenient implementation of the
 * {@link org.springframework.aop.IntroductionInterceptor} interface.
 *
 * <p>This differs from {@link DelegatingIntroductionInterceptor} in that a single
 * instance of this class can be used to advise multiple target objects, and each target
 * object will have its <i>own</i> delegate (whereas DelegatingIntroductionInterceptor
 * shares the same delegate, and hence the same state across all targets).
 *
 * <p>The {@code suppressInterface} method can be used to suppress interfaces
 * implemented by the delegate class but which should not be introduced to the
 * owning AOP proxy.
 *
 * <p>An instance of this class is serializable if the delegates are.
 *
 * <p><i>Note: There are some implementation similarities between this class and
 * {@link DelegatingIntroductionInterceptor} that suggest a possible refactoring
 * to extract a common ancestor class in the future.</i>
 *
 * @author Adrian Colyer
 * @author Juergen Hoeller
 * @since 2.0
 * @see #suppressInterface
 * @see DelegatingIntroductionInterceptor
 */
@SuppressWarnings("serial")
public class DelegatePerTargetObjectIntroductionInterceptor extends IntroductionInfoSupport
		implements IntroductionInterceptor {

	
Hold weak references to keys as we don't want to interfere with garbage collection..
/**
	 * Hold weak references to keys as we don't want to interfere with garbage collection..
	 */
	private final Map<Object, Object> delegateMap = new WeakHashMap<>();

	private Class<?> defaultImplType;

	private Class<?> interfaceType;


	public DelegatePerTargetObjectIntroductionInterceptor(Class<?> defaultImplType, Class<?> interfaceType) {
		this.defaultImplType = defaultImplType;
		this.interfaceType = interfaceType;
		// Create a new delegate now (but don't store it in the map).
		// We do this for two reasons:
		// 1) to fail early if there is a problem instantiating delegates
		// 2) to populate the interface map once and once only
		Object delegate = createNewDelegate();
		implementInterfacesOnObject(delegate);
		suppressInterface(IntroductionInterceptor.class);
		suppressInterface(DynamicIntroductionAdvice.class);
	}


	
Subclasses may need to override this if they want to perform custom
behaviour in around advice. However, subclasses should invoke this
method, which handles introduced interfaces and forwarding to the target.
/**
	 * Subclasses may need to override this if they want to perform custom
	 * behaviour in around advice. However, subclasses should invoke this
	 * method, which handles introduced interfaces and forwarding to the target.
	 */
	@Override
	@Nullable
	public Object invoke(MethodInvocation mi) throws Throwable {
		if (isMethodOnIntroducedInterface(mi)) {
			Object delegate = getIntroductionDelegateFor(mi.getThis());

			// Using the following method rather than direct reflection,
			// we get correct handling of InvocationTargetException
			// if the introduced method throws an exception.
			Object retVal = AopUtils.invokeJoinpointUsingReflection(delegate, mi.getMethod(), mi.getArguments());

			// Massage return value if possible: if the delegate returned itself,
			// we really want to return the proxy.
			if (retVal == delegate && mi instanceof ProxyMethodInvocation) {
				retVal = ((ProxyMethodInvocation) mi).getProxy();
			}
			return retVal;
		}

		return doProceed(mi);
	}

	
Proceed with the supplied MethodInterceptor. Subclasses can override this method to intercept method invocations on the target object which is useful when an introduction needs to monitor the object that it is introduced into. This method is never called for MethodInvocations on the introduced interfaces. /**
	 * Proceed with the supplied {@link org.aopalliance.intercept.MethodInterceptor}.
	 * Subclasses can override this method to intercept method invocations on the
	 * target object which is useful when an introduction needs to monitor the object
	 * that it is introduced into. This method is <strong>never</strong> called for
	 * {@link MethodInvocation MethodInvocations} on the introduced interfaces.
	 */
	@Nullable
	protected Object doProceed(MethodInvocation mi) throws Throwable {
		// If we get here, just pass the invocation on.
		return mi.proceed();
	}

	private Object getIntroductionDelegateFor(@Nullable Object targetObject) {
		synchronized (this.delegateMap) {
			if (this.delegateMap.containsKey(targetObject)) {
				return this.delegateMap.get(targetObject);
			}
			else {
				Object delegate = createNewDelegate();
				this.delegateMap.put(targetObject, delegate);
				return delegate;
			}
		}
	}

	private Object createNewDelegate() {
		try {
			return ReflectionUtils.accessibleConstructor(this.defaultImplType).newInstance();
		}
		catch (Throwable ex) {
			throw new IllegalArgumentException("Cannot create default implementation for '" +
					this.interfaceType.getName() + "' mixin (" + this.defaultImplType.getName() + "): " + ex);
		}
	}

}