/*
    * Copyright 2006-2013 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.batch.item.adapter;
  
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.List;
  
  import org.springframework.beans.factory.InitializingBean;
  import org.springframework.util.Assert;
  import org.springframework.util.MethodInvoker;
  
  /**
   * Superclass for delegating classes which dynamically call a custom method of
   * injected object. Provides convenient API for dynamic method invocation
   * shielding subclasses from low-level details and exception handling.
   *
   * {@link Exception}s thrown by a successfully invoked delegate method are
   * re-thrown without wrapping. In case the delegate method throws a
   * {@link Throwable} that doesn't subclass {@link Exception} it will be wrapped
   * by {@link InvocationTargetThrowableWrapper}.
   *
   * @author Robert Kasanicky
   */
  public abstract class AbstractMethodInvokingDelegator<T> implements InitializingBean {
  
  	private Object targetObject;
  
  	private String targetMethod;
  
  	private Object[] arguments;
  
  	/**
  	 * Invoker the target method with arguments set by
  	 * {@link #setArguments(Object[])}.
  	 * @return object returned by invoked method
  	 * @throws DynamicMethodInvocationException if the {@link MethodInvoker}
  	 * used throws exception
  	 */
  	protected T invokeDelegateMethod() throws Exception {
  		MethodInvoker invoker = createMethodInvoker(targetObject, targetMethod);
  		invoker.setArguments(arguments);
  		return doInvoke(invoker);
  	}
  
  	/**
  	 * Invokes the target method with given argument.
  	 * @param object argument for the target method
  	 * @return object returned by target method
  	 * @throws DynamicMethodInvocationException if the {@link MethodInvoker}
  	 * used throws exception
  	 */
  	protected T invokeDelegateMethodWithArgument(Object object) throws Exception {
  		MethodInvoker invoker = createMethodInvoker(targetObject, targetMethod);
  		invoker.setArguments(new Object[] { object });
  		return doInvoke(invoker);
  	}
  
  	/**
  	 * Invokes the target method with given arguments.
  	 * @param args arguments for the invoked method
  	 * @return object returned by invoked method
  	 * @throws DynamicMethodInvocationException if the {@link MethodInvoker}
  	 * used throws exception
  	 */
  	protected T invokeDelegateMethodWithArguments(Object[] args) throws Exception {
  		MethodInvoker invoker = createMethodInvoker(targetObject, targetMethod);
  		invoker.setArguments(args);
  		return doInvoke(invoker);
  	}
  
  	/**
  	 * Create a new configured instance of {@link MethodInvoker}.
  	 */
  	private MethodInvoker createMethodInvoker(Object targetObject, String targetMethod) {
  		HippyMethodInvoker invoker = new HippyMethodInvoker();
  		invoker.setTargetObject(targetObject);
  		invoker.setTargetMethod(targetMethod);
  		invoker.setArguments(arguments);
  		return invoker;
  	}
  
  	/**
 	 * Prepare and invoke the invoker, rethrow checked exceptions as unchecked.
 	 * @param invoker configured invoker
 	 * @return return value of the invoked method
 	 */
 	@SuppressWarnings("unchecked")
 	private T doInvoke(MethodInvoker invoker) throws Exception {
 		try {
 			invoker.prepare();
 		}
 		catch (ClassNotFoundException e) {
 			throw new DynamicMethodInvocationException(e);
 		}
 		catch (NoSuchMethodException e) {
 			throw new DynamicMethodInvocationException(e);
 		}
 
 		try {
 			return (T) invoker.invoke();
 		}
 		catch (InvocationTargetException e) {
 			if (e.getCause() instanceof Exception) {
 				throw (Exception) e.getCause();
 			}
 			else {
 				throw new InvocationTargetThrowableWrapper(e.getCause());
 			}
 		}
 		catch (IllegalAccessException e) {
 			throw new DynamicMethodInvocationException(e);
 		}
 	}
 
 	@Override
 	public void afterPropertiesSet() throws Exception {
 		Assert.notNull(targetObject);
 		Assert.hasLength(targetMethod);
 		Assert.state(targetClassDeclaresTargetMethod(),
 				"target class must declare a method with matching name and parameter types");
 	}
 
 	/**
 	 * @return true if target class declares a method matching target method
 	 * name with given number of arguments of appropriate type.
 	 */
 	private boolean targetClassDeclaresTargetMethod() {
 		MethodInvoker invoker = createMethodInvoker(targetObject, targetMethod);
 
 		Method[] memberMethods = invoker.getTargetClass().getMethods();
 		Method[] declaredMethods = invoker.getTargetClass().getDeclaredMethods();
 
 		List<Method> allMethods = new ArrayList<Method>();
 		allMethods.addAll(Arrays.asList(memberMethods));
 		allMethods.addAll(Arrays.asList(declaredMethods));
 
 		String targetMethodName = invoker.getTargetMethod();
 
 		for (Method method : allMethods) {
 			if (method.getName().equals(targetMethodName)) {
 				Class<?>[] params = method.getParameterTypes();
 				if (arguments == null) {
 					// don't check signature, assume arguments will be supplied
 					// correctly at runtime
 					return true;
 				}
 				if (arguments.length == params.length) {
 					boolean argumentsMatchParameters = true;
 					for (int j = 0; j < params.length; j++) {
 						if (arguments[j] == null) {
 							continue;
 						}
 						if (!(params[j].isAssignableFrom(arguments[j].getClass()))) {
 							argumentsMatchParameters = false;
 						}
 					}
 					if (argumentsMatchParameters) {
 						return true;
 					}
 				}
 			}
 		}
 
 		return false;
 	}
 
 	/**
 	 * @param targetObject the delegate - bean id can be used to set this value
 	 * in Spring configuration
 	 */
 	public void setTargetObject(Object targetObject) {
 		this.targetObject = targetObject;
 	}
 
 	/**
 	 * @param targetMethod name of the method to be invoked on
 	 * {@link #setTargetObject(Object)}.
 	 */
 	public void setTargetMethod(String targetMethod) {
 		this.targetMethod = targetMethod;
 	}
 
 	/**
 	 * @param arguments arguments values for the {
 	 * {@link #setTargetMethod(String)}. These will be used only when the
 	 * subclass tries to invoke the target method without providing explicit
 	 * argument values.
 	 *
 	 * If arguments are set to not-null value {@link #afterPropertiesSet()} will
 	 * check the values are compatible with target method's signature. In case
 	 * arguments are null (not set) method signature will not be checked and it
 	 * is assumed correct values will be supplied at runtime.
 	 */
 	public void setArguments(Object[] arguments) {
 		this.arguments = arguments == null ? null : Arrays.asList(arguments).toArray();
 	}
 
 	/**
 	 * Used to wrap a {@link Throwable} (not an {@link Exception}) thrown by a
 	 * reflectively-invoked delegate.
 	 *
 	 * @author Robert Kasanicky
 	 */
 	public static class InvocationTargetThrowableWrapper extends RuntimeException {
 
 		public InvocationTargetThrowableWrapper(Throwable cause) {
 			super(cause);
 		}
 
 	}
 }