/*
 * Copyright 2002-2018 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
 *
 *      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.springframework.beans.factory.support;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.beans.BeanInstantiationException;
import org.springframework.beans.BeanUtils;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.cglib.core.ClassGenerator;
import org.springframework.cglib.core.DefaultGeneratorStrategy;
import org.springframework.cglib.core.SpringNamingPolicy;
import org.springframework.cglib.proxy.Callback;
import org.springframework.cglib.proxy.CallbackFilter;
import org.springframework.cglib.proxy.Enhancer;
import org.springframework.cglib.proxy.Factory;
import org.springframework.cglib.proxy.MethodInterceptor;
import org.springframework.cglib.proxy.MethodProxy;
import org.springframework.cglib.proxy.NoOp;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;

Default object instantiation strategy for use in BeanFactories.
Uses CGLIB to generate subclasses dynamically if methods need to be
overridden by the container to implement Method Injection.
Author:
Rod Johnson, Juergen Hoeller, Sam Brannen
Since:
1.1/**
 * Default object instantiation strategy for use in BeanFactories.
 *
 * <p>Uses CGLIB to generate subclasses dynamically if methods need to be
 * overridden by the container to implement <em>Method Injection</em>.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Sam Brannen
 * @since 1.1
 */
public class CglibSubclassingInstantiationStrategy extends SimpleInstantiationStrategy {

	
Index in the CGLIB callback array for passthrough behavior,
in which case the subclass won't override the original class.
/**
	 * Index in the CGLIB callback array for passthrough behavior,
	 * in which case the subclass won't override the original class.
	 */
	private static final int PASSTHROUGH = 0;

	
Index in the CGLIB callback array for a method that should
be overridden to provide method lookup.
/**
	 * Index in the CGLIB callback array for a method that should
	 * be overridden to provide <em>method lookup</em>.
	 */
	private static final int LOOKUP_OVERRIDE = 1;

	
Index in the CGLIB callback array for a method that should
be overridden using generic method replacer functionality.
/**
	 * Index in the CGLIB callback array for a method that should
	 * be overridden using generic <em>method replacer</em> functionality.
	 */
	private static final int METHOD_REPLACER = 2;


	@Override
	protected Object instantiateWithMethodInjection(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {
		return instantiateWithMethodInjection(bd, beanName, owner, null);
	}

	@Override
	protected Object instantiateWithMethodInjection(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner,
			@Nullable Constructor<?> ctor, Object... args) {

		// Must generate CGLIB subclass...
		return new CglibSubclassCreator(bd, owner).instantiate(ctor, args);
	}


	
An inner class created for historical reasons to avoid external CGLIB dependency
in Spring versions earlier than 3.2.
/**
	 * An inner class created for historical reasons to avoid external CGLIB dependency
	 * in Spring versions earlier than 3.2.
	 */
	private static class CglibSubclassCreator {

		private static final Class<?>[] CALLBACK_TYPES = new Class<?>[]
				{NoOp.class, LookupOverrideMethodInterceptor.class, ReplaceOverrideMethodInterceptor.class};

		private final RootBeanDefinition beanDefinition;

		private final BeanFactory owner;

		CglibSubclassCreator(RootBeanDefinition beanDefinition, BeanFactory owner) {
			this.beanDefinition = beanDefinition;
			this.owner = owner;
		}

		
Create a new instance of a dynamically generated subclass implementing the
required lookups.
Params:
ctor – constructor to use. If this is null, use the no-arg constructor (no parameterization, or Setter Injection)
args – arguments to use for the constructor. Ignored if the ctor parameter is null.
Returns:
new instance of the dynamically generated subclass/**
		 * Create a new instance of a dynamically generated subclass implementing the
		 * required lookups.
		 * @param ctor constructor to use. If this is {@code null}, use the
		 * no-arg constructor (no parameterization, or Setter Injection)
		 * @param args arguments to use for the constructor.
		 * Ignored if the {@code ctor} parameter is {@code null}.
		 * @return new instance of the dynamically generated subclass
		 */
		public Object instantiate(@Nullable Constructor<?> ctor, Object... args) {
			Class<?> subclass = createEnhancedSubclass(this.beanDefinition);
			Object instance;
			if (ctor == null) {
				instance = BeanUtils.instantiateClass(subclass);
			}
			else {
				try {
					Constructor<?> enhancedSubclassConstructor = subclass.getConstructor(ctor.getParameterTypes());
					instance = enhancedSubclassConstructor.newInstance(args);
				}
				catch (Exception ex) {
					throw new BeanInstantiationException(this.beanDefinition.getBeanClass(),
							"Failed to invoke constructor for CGLIB enhanced subclass [" + subclass.getName() + "]", ex);
				}
			}
			// SPR-10785: set callbacks directly on the instance instead of in the
			// enhanced class (via the Enhancer) in order to avoid memory leaks.
			Factory factory = (Factory) instance;
			factory.setCallbacks(new Callback[] {NoOp.INSTANCE,
					new LookupOverrideMethodInterceptor(this.beanDefinition, this.owner),
					new ReplaceOverrideMethodInterceptor(this.beanDefinition, this.owner)});
			return instance;
		}

		
Create an enhanced subclass of the bean class for the provided bean
definition, using CGLIB.
/**
		 * Create an enhanced subclass of the bean class for the provided bean
		 * definition, using CGLIB.
		 */
		private Class<?> createEnhancedSubclass(RootBeanDefinition beanDefinition) {
			Enhancer enhancer = new Enhancer();
			enhancer.setSuperclass(beanDefinition.getBeanClass());
			enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
			if (this.owner instanceof ConfigurableBeanFactory) {
				ClassLoader cl = ((ConfigurableBeanFactory) this.owner).getBeanClassLoader();
				enhancer.setStrategy(new ClassLoaderAwareGeneratorStrategy(cl));
			}
			enhancer.setCallbackFilter(new MethodOverrideCallbackFilter(beanDefinition));
			enhancer.setCallbackTypes(CALLBACK_TYPES);
			return enhancer.createClass();
		}
	}


	
Class providing hashCode and equals methods required by CGLIB to
ensure that CGLIB doesn't generate a distinct class per bean.
Identity is based on class and bean definition.
/**
	 * Class providing hashCode and equals methods required by CGLIB to
	 * ensure that CGLIB doesn't generate a distinct class per bean.
	 * Identity is based on class and bean definition.
	 */
	private static class CglibIdentitySupport {

		private final RootBeanDefinition beanDefinition;

		public CglibIdentitySupport(RootBeanDefinition beanDefinition) {
			this.beanDefinition = beanDefinition;
		}

		public RootBeanDefinition getBeanDefinition() {
			return this.beanDefinition;
		}

		@Override
		public boolean equals(Object other) {
			return (getClass() == other.getClass() &&
					this.beanDefinition.equals(((CglibIdentitySupport) other).beanDefinition));
		}

		@Override
		public int hashCode() {
			return this.beanDefinition.hashCode();
		}
	}


	
CGLIB GeneratorStrategy variant which exposes the application ClassLoader
as thread context ClassLoader for the time of class generation
(in order for ASM to pick it up when doing common superclass resolution).
/**
	 * CGLIB GeneratorStrategy variant which exposes the application ClassLoader
	 * as thread context ClassLoader for the time of class generation
	 * (in order for ASM to pick it up when doing common superclass resolution).
	 */
	private static class ClassLoaderAwareGeneratorStrategy extends DefaultGeneratorStrategy {

		@Nullable
		private final ClassLoader classLoader;

		public ClassLoaderAwareGeneratorStrategy(@Nullable ClassLoader classLoader) {
			this.classLoader = classLoader;
		}

		@Override
		public byte[] generate(ClassGenerator cg) throws Exception {
			if (this.classLoader == null) {
				return super.generate(cg);
			}

			Thread currentThread = Thread.currentThread();
			ClassLoader threadContextClassLoader;
			try {
				threadContextClassLoader = currentThread.getContextClassLoader();
			}
			catch (Throwable ex) {
				// Cannot access thread context ClassLoader - falling back...
				return super.generate(cg);
			}

			boolean overrideClassLoader = !this.classLoader.equals(threadContextClassLoader);
			if (overrideClassLoader) {
				currentThread.setContextClassLoader(this.classLoader);
			}
			try {
				return super.generate(cg);
			}
			finally {
				if (overrideClassLoader) {
					// Reset original thread context ClassLoader.
					currentThread.setContextClassLoader(threadContextClassLoader);
				}
			}
		}
	}


	
CGLIB callback for filtering method interception behavior.
/**
	 * CGLIB callback for filtering method interception behavior.
	 */
	private static class MethodOverrideCallbackFilter extends CglibIdentitySupport implements CallbackFilter {

		private static final Log logger = LogFactory.getLog(MethodOverrideCallbackFilter.class);

		public MethodOverrideCallbackFilter(RootBeanDefinition beanDefinition) {
			super(beanDefinition);
		}

		@Override
		public int accept(Method method) {
			MethodOverride methodOverride = getBeanDefinition().getMethodOverrides().getOverride(method);
			if (logger.isTraceEnabled()) {
				logger.trace("Override for '" + method.getName() + "' is [" + methodOverride + "]");
			}
			if (methodOverride == null) {
				return PASSTHROUGH;
			}
			else if (methodOverride instanceof LookupOverride) {
				return LOOKUP_OVERRIDE;
			}
			else if (methodOverride instanceof ReplaceOverride) {
				return METHOD_REPLACER;
			}
			throw new UnsupportedOperationException("Unexpected MethodOverride subclass: " +
					methodOverride.getClass().getName());
		}
	}


	
CGLIB MethodInterceptor to override methods, replacing them with an
implementation that returns a bean looked up in the container.
/**
	 * CGLIB MethodInterceptor to override methods, replacing them with an
	 * implementation that returns a bean looked up in the container.
	 */
	private static class LookupOverrideMethodInterceptor extends CglibIdentitySupport implements MethodInterceptor {

		private final BeanFactory owner;

		public LookupOverrideMethodInterceptor(RootBeanDefinition beanDefinition, BeanFactory owner) {
			super(beanDefinition);
			this.owner = owner;
		}

		@Override
		public Object intercept(Object obj, Method method, Object[] args, MethodProxy mp) throws Throwable {
			// Cast is safe, as CallbackFilter filters are used selectively.
			LookupOverride lo = (LookupOverride) getBeanDefinition().getMethodOverrides().getOverride(method);
			Assert.state(lo != null, "LookupOverride not found");
			Object[] argsToUse = (args.length > 0 ? args : null);  // if no-arg, don't insist on args at all
			if (StringUtils.hasText(lo.getBeanName())) {
				return (argsToUse != null ? this.owner.getBean(lo.getBeanName(), argsToUse) :
						this.owner.getBean(lo.getBeanName()));
			}
			else {
				return (argsToUse != null ? this.owner.getBean(method.getReturnType(), argsToUse) :
						this.owner.getBean(method.getReturnType()));
			}
		}
	}


	
CGLIB MethodInterceptor to override methods, replacing them with a call
to a generic MethodReplacer.
/**
	 * CGLIB MethodInterceptor to override methods, replacing them with a call
	 * to a generic MethodReplacer.
	 */
	private static class ReplaceOverrideMethodInterceptor extends CglibIdentitySupport implements MethodInterceptor {

		private final BeanFactory owner;

		public ReplaceOverrideMethodInterceptor(RootBeanDefinition beanDefinition, BeanFactory owner) {
			super(beanDefinition);
			this.owner = owner;
		}

		@Override
		public Object intercept(Object obj, Method method, Object[] args, MethodProxy mp) throws Throwable {
			ReplaceOverride ro = (ReplaceOverride) getBeanDefinition().getMethodOverrides().getOverride(method);
			Assert.state(ro != null, "ReplaceOverride not found");
			// TODO could cache if a singleton for minor performance optimization
			MethodReplacer mr = this.owner.getBean(ro.getMethodReplacerBeanName(), MethodReplacer.class);
			return mr.reimplement(obj, method, args);
		}
	}

}