/*
 * Copyright 2002-2012 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.web.servlet.mvc.multiaction;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

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

import org.springframework.beans.BeanUtils;
import org.springframework.util.Assert;
import org.springframework.util.ReflectionUtils;
import org.springframework.validation.ValidationUtils;
import org.springframework.validation.Validator;
import org.springframework.web.HttpSessionRequiredException;
import org.springframework.web.bind.ServletRequestDataBinder;
import org.springframework.web.bind.support.WebBindingInitializer;
import org.springframework.web.context.request.ServletWebRequest;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.AbstractController;
import org.springframework.web.servlet.mvc.LastModified;

/**
 * {@link org.springframework.web.servlet.mvc.Controller Controller}
 * implementation that allows multiple request types to be handled by the same
 * class. Subclasses of this class can handle several different types of
 * request with methods of the form
 *
 * <pre class="code">public (ModelAndView | Map | String | void) actionName(HttpServletRequest request, HttpServletResponse response, [,HttpSession] [,AnyObject]);</pre>
 *
 * A Map return value indicates a model that is supposed to be passed to a default view
 * (determined through a {@link org.springframework.web.servlet.RequestToViewNameTranslator}).
 * A String return value indicates the name of a view to be rendered without a specific model.
 *
 * <p>May take a third parameter (of type {@link HttpSession}) in which an
 * existing session will be required, or a third parameter of an arbitrary
 * class that gets treated as the command (that is, an instance of the class
 * gets created, and request parameters get bound to it)
 *
 * <p>These methods can throw any kind of exception, but should only let
 * propagate those that they consider fatal, or which their class or superclass
 * is prepared to catch by implementing an exception handler.
 *
 * <p>When returning just a {@link Map} instance view name translation will be
 * used to generate the view name. The configured
 * {@link org.springframework.web.servlet.RequestToViewNameTranslator} will be
 * used to determine the view name.
 *
 * <p>When returning {@code void} a return value of {@code null} is
 * assumed meaning that the handler method is responsible for writing the
 * response directly to the supplied {@link HttpServletResponse}.
 *
 * <p>This model allows for rapid coding, but loses the advantage of
 * compile-time checking. It is similar to a Struts {@code DispatchAction},
 * but more sophisticated. Also supports delegation to another object.
 *
 * <p>An implementation of the {@link MethodNameResolver} interface defined in
 * this package should return a method name for a given request, based on any
 * aspect of the request, such as its URL or an "action" parameter. The actual
 * strategy can be configured via the "methodNameResolver" bean property, for
 * each {@code MultiActionController}.
 *
 * <p>The default {@code MethodNameResolver} is
 * {@link InternalPathMethodNameResolver}; further included strategies are
 * {@link PropertiesMethodNameResolver} and {@link ParameterMethodNameResolver}.
 *
 * <p>Subclasses can implement custom exception handler methods with names such
 * as:
 *
 * <pre class="code">public ModelAndView anyMeaningfulName(HttpServletRequest request, HttpServletResponse response, ExceptionClass exception);</pre>
 *
 * The third parameter can be any subclass or {@link Exception} or
 * {@link RuntimeException}.
 *
 * <p>There can also be an optional {@code xxxLastModified} method for
 * handlers, of signature:
 *
 * <pre class="code">public long anyMeaningfulNameLastModified(HttpServletRequest request)</pre>
 *
 * If such a method is present, it will be invoked. Default return from
 * {@code getLastModified} is -1, meaning that the content must always be
 * regenerated.
 *
 * <p><b>Note that all handler methods need to be public and that
 * method overloading is <i>not</i> allowed.</b>
 *
 * <p>See also the description of the workflow performed by
 * {@link AbstractController the superclass} (in that section of the class
 * level Javadoc entitled 'workflow').
 *
 * <p><b>Note:</b> For maximum data binding flexibility, consider direct usage of a
 * {@link ServletRequestDataBinder} in your controller method, instead of relying
 * on a declared command argument. This allows for full control over the entire
 * binder setup and usage, including the invocation of {@link Validator Validators}
 * and the subsequent evaluation of binding/validation errors.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Colin Sampaleanu
 * @author Rob Harrop
 * @author Sam Brannen
 * @see MethodNameResolver
 * @see InternalPathMethodNameResolver
 * @see PropertiesMethodNameResolver
 * @see ParameterMethodNameResolver
 * @see org.springframework.web.servlet.mvc.LastModified#getLastModified
 * @see org.springframework.web.bind.ServletRequestDataBinder
 */
public class MultiActionController extends AbstractController implements LastModified {

	/** Suffix for last-modified methods */
	public static final String LAST_MODIFIED_METHOD_SUFFIX = "LastModified";

	/** Default command name used for binding command objects: "command" */
	public static final String DEFAULT_COMMAND_NAME = "command";

	/**
	 * Log category to use when no mapped handler is found for a request.
	 * @see #pageNotFoundLogger
	 */
	public static final String PAGE_NOT_FOUND_LOG_CATEGORY = "org.springframework.web.servlet.PageNotFound";


	/**
	 * Additional logger to use when no mapped handler is found for a request.
	 * @see #PAGE_NOT_FOUND_LOG_CATEGORY
	 */
	protected static final Log pageNotFoundLogger = LogFactory.getLog(PAGE_NOT_FOUND_LOG_CATEGORY);

	/** Object we'll invoke methods on. Defaults to this. */
	private Object delegate;

	/** Delegate that knows how to determine method names from incoming requests */
	private MethodNameResolver methodNameResolver = new InternalPathMethodNameResolver();

	/** List of Validators to apply to commands */
	private Validator[] validators;

	/** Optional strategy for pre-initializing data binding */
	private WebBindingInitializer webBindingInitializer;

	/** Handler methods, keyed by name */
	private final Map<String, Method> handlerMethodMap = new HashMap<String, Method>();

	/** LastModified methods, keyed by handler method name (without LAST_MODIFIED_SUFFIX) */
	private final Map<String, Method> lastModifiedMethodMap = new HashMap<String, Method>();

	/** Methods, keyed by exception class */
	private final Map<Class<?>, Method> exceptionHandlerMap = new HashMap<Class<?>, Method>();


	/**
	 * Constructor for {@code MultiActionController} that looks for
	 * handler methods in the present subclass.
	 */
	public MultiActionController() {
		this.delegate = this;
		registerHandlerMethods(this.delegate);
		// We'll accept no handler methods found here - a delegate might be set later on.
	}

	/**
	 * Constructor for {@code MultiActionController} that looks for
	 * handler methods in delegate, rather than a subclass of this class.
	 * @param delegate handler object. This does not need to implement any
	 * particular interface, as everything is done using reflection.
	 */
	public MultiActionController(Object delegate) {
		setDelegate(delegate);
	}


	/**
	 * Set the delegate used by this class; the default is {@code this},
	 * assuming that handler methods have been added by a subclass.
	 * <p>This method does not get invoked once the class is configured.
	 * @param delegate an object containing handler methods
	 * @throws IllegalStateException if no handler methods are found
	 */
	public final void setDelegate(Object delegate) {
		Assert.notNull(delegate, "Delegate must not be null");
		this.delegate = delegate;
		registerHandlerMethods(this.delegate);
		// There must be SOME handler methods.
		if (this.handlerMethodMap.isEmpty()) {
			throw new IllegalStateException("No handler methods in class [" + this.delegate.getClass() + "]");
		}
	}

	/**
	 * Set the method name resolver that this class should use.
	 * <p>Allows parameterization of handler method mappings.
	 */
	public final void setMethodNameResolver(MethodNameResolver methodNameResolver) {
		this.methodNameResolver = methodNameResolver;
	}

	/**
	 * Return the MethodNameResolver used by this class.
	 */
	public final MethodNameResolver getMethodNameResolver() {
		return this.methodNameResolver;
	}

	/**
	 * Set the {@link Validator Validators} for this controller.
	 * <p>The {@code Validators} must support the specified command class.
	 */
	public final void setValidators(Validator[] validators) {
		this.validators = validators;
	}

	/**
	 * Return the Validators for this controller.
	 */
	public final Validator[] getValidators() {
		return this.validators;
	}

	/**
	 * Specify a WebBindingInitializer which will apply pre-configured
	 * configuration to every DataBinder that this controller uses.
	 * <p>Allows for factoring out the entire binder configuration
	 * to separate objects, as an alternative to {@link #initBinder}.
	 */
	public final void setWebBindingInitializer(WebBindingInitializer webBindingInitializer) {
		this.webBindingInitializer = webBindingInitializer;
	}

	/**
	 * Return the WebBindingInitializer (if any) which will apply pre-configured
	 * configuration to every DataBinder that this controller uses.
	 */
	public final WebBindingInitializer getWebBindingInitializer() {
		return this.webBindingInitializer;
	}


	/**
	 * Registers all handlers methods on the delegate object.
	 */
	private void registerHandlerMethods(Object delegate) {
		this.handlerMethodMap.clear();
		this.lastModifiedMethodMap.clear();
		this.exceptionHandlerMap.clear();

		// Look at all methods in the subclass, trying to find
		// methods that are validators according to our criteria
		Method[] methods = delegate.getClass().getMethods();
		for (Method method : methods) {
			// We're looking for methods with given parameters.
			if (isExceptionHandlerMethod(method)) {
				registerExceptionHandlerMethod(method);
			}
			else if (isHandlerMethod(method)) {
				registerHandlerMethod(method);
				registerLastModifiedMethodIfExists(delegate, method);
			}
		}
	}

	/**
	 * Is the supplied method a valid handler method?
	 * <p>Does not consider {@code Controller.handleRequest} itself
	 * as handler method (to avoid potential stack overflow).
	 */
	private boolean isHandlerMethod(Method method) {
		Class<?> returnType = method.getReturnType();
		if (ModelAndView.class.equals(returnType) || Map.class.equals(returnType) || String.class.equals(returnType) ||
				void.class.equals(returnType)) {
			Class<?>[] parameterTypes = method.getParameterTypes();
			return (parameterTypes.length >= 2 &&
					HttpServletRequest.class.equals(parameterTypes[0]) &&
					HttpServletResponse.class.equals(parameterTypes[1]) &&
					!("handleRequest".equals(method.getName()) && parameterTypes.length == 2));
		}
		return false;
	}

	/**
	 * Is the supplied method a valid exception handler method?
	 */
	private boolean isExceptionHandlerMethod(Method method) {
		return (isHandlerMethod(method) &&
				method.getParameterTypes().length == 3 &&
				Throwable.class.isAssignableFrom(method.getParameterTypes()[2]));
	}

	/**
	 * Registers the supplied method as a request handler.
	 */
	private void registerHandlerMethod(Method method) {
		if (logger.isDebugEnabled()) {
			logger.debug("Found action method [" + method + "]");
		}
		this.handlerMethodMap.put(method.getName(), method);
	}

	/**
	 * Registers a last-modified handler method for the supplied handler method
	 * if one exists.
	 */
	private void registerLastModifiedMethodIfExists(Object delegate, Method method) {
		// Look for corresponding LastModified method.
		try {
			Method lastModifiedMethod = delegate.getClass().getMethod(
					method.getName() + LAST_MODIFIED_METHOD_SUFFIX,
					new Class<?>[] {HttpServletRequest.class});
			Class<?> returnType = lastModifiedMethod.getReturnType();
			if (!(long.class.equals(returnType) || Long.class.equals(returnType))) {
				throw new IllegalStateException("last-modified method [" + lastModifiedMethod +
						"] declares an invalid return type - needs to be 'long' or 'Long'");
			}
			// Put in cache, keyed by handler method name.
			this.lastModifiedMethodMap.put(method.getName(), lastModifiedMethod);
			if (logger.isDebugEnabled()) {
				logger.debug("Found last-modified method for handler method [" + method + "]");
			}
		}
		catch (NoSuchMethodException ex) {
			// No last modified method. That's ok.
		}
	}

	/**
	 * Registers the supplied method as an exception handler.
	 */
	private void registerExceptionHandlerMethod(Method method) {
		this.exceptionHandlerMap.put(method.getParameterTypes()[2], method);
		if (logger.isDebugEnabled()) {
			logger.debug("Found exception handler method [" + method + "]");
		}
	}


	//---------------------------------------------------------------------
	// Implementation of LastModified
	//---------------------------------------------------------------------

	/**
	 * Try to find an XXXXLastModified method, where XXXX is the name of a handler.
	 * Return -1 if there's no such handler, indicating that content must be updated.
	 * @see org.springframework.web.servlet.mvc.LastModified#getLastModified(HttpServletRequest)
	 */
	@Override
	public long getLastModified(HttpServletRequest request) {
		try {
			String handlerMethodName = this.methodNameResolver.getHandlerMethodName(request);
			Method lastModifiedMethod = this.lastModifiedMethodMap.get(handlerMethodName);
			if (lastModifiedMethod != null) {
				try {
					// Invoke the last-modified method...
					Long wrappedLong = (Long) lastModifiedMethod.invoke(this.delegate, request);
					return (wrappedLong != null ? wrappedLong : -1);
				}
				catch (Exception ex) {
					// We encountered an error invoking the last-modified method.
					// We can't do anything useful except log this, as we can't throw an exception.
					logger.error("Failed to invoke last-modified method", ex);
				}
			}
		}
		catch (NoSuchRequestHandlingMethodException ex) {
			// No handler method for this request. This shouldn't happen, as this
			// method shouldn't be called unless a previous invocation of this class
			// has generated content. Do nothing, that's OK: We'll return default.
		}
		return -1L;
	}


	//---------------------------------------------------------------------
	// Implementation of AbstractController
	//---------------------------------------------------------------------

	/**
	 * Determine a handler method and invoke it.
	 * @see MethodNameResolver#getHandlerMethodName
	 * @see #invokeNamedMethod
	 * @see #handleNoSuchRequestHandlingMethod
	 */
	@Override
	protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
			throws Exception {
		try {
			String methodName = this.methodNameResolver.getHandlerMethodName(request);
			return invokeNamedMethod(methodName, request, response);
		}
		catch (NoSuchRequestHandlingMethodException ex) {
			return handleNoSuchRequestHandlingMethod(ex, request, response);
		}
	}

	/**
	 * Handle the case where no request handler method was found.
	 * <p>The default implementation logs a warning and sends an HTTP 404 error.
	 * Alternatively, a fallback view could be chosen, or the
	 * NoSuchRequestHandlingMethodException could be rethrown as-is.
	 * @param ex the NoSuchRequestHandlingMethodException to be handled
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @return a ModelAndView to render, or {@code null} if handled directly
	 * @throws Exception an Exception that should be thrown as result of the servlet request
	 */
	protected ModelAndView handleNoSuchRequestHandlingMethod(
			NoSuchRequestHandlingMethodException ex, HttpServletRequest request, HttpServletResponse response)
			throws Exception {

		pageNotFoundLogger.warn(ex.getMessage());
		response.sendError(HttpServletResponse.SC_NOT_FOUND);
		return null;
	}

	/**
	 * Invokes the named method.
	 * <p>Uses a custom exception handler if possible; otherwise, throw an
	 * unchecked exception; wrap a checked exception or Throwable.
	 */
	protected final ModelAndView invokeNamedMethod(
			String methodName, HttpServletRequest request, HttpServletResponse response) throws Exception {

		Method method = this.handlerMethodMap.get(methodName);
		if (method == null) {
			throw new NoSuchRequestHandlingMethodException(methodName, getClass());
		}

		try {
			Class<?>[] paramTypes = method.getParameterTypes();
			List<Object> params = new ArrayList<Object>(4);
			params.add(request);
			params.add(response);

			if (paramTypes.length >= 3 && paramTypes[2].equals(HttpSession.class)) {
				HttpSession session = request.getSession(false);
				if (session == null) {
					throw new HttpSessionRequiredException(
							"Pre-existing session required for handler method '" + methodName + "'");
				}
				params.add(session);
			}

			// If last parameter isn't of HttpSession type, it's a command.
			if (paramTypes.length >= 3 &&
					!paramTypes[paramTypes.length - 1].equals(HttpSession.class)) {
				Object command = newCommandObject(paramTypes[paramTypes.length - 1]);
				params.add(command);
				bind(request, command);
			}

			Object returnValue = method.invoke(this.delegate, params.toArray(new Object[params.size()]));
			return massageReturnValueIfNecessary(returnValue);
		}
		catch (InvocationTargetException ex) {
			// The handler method threw an exception.
			return handleException(request, response, ex.getTargetException());
		}
		catch (Exception ex) {
			// The binding process threw an exception.
			return handleException(request, response, ex);
		}
	}

	/**
	 * Processes the return value of a handler method to ensure that it either returns
	 * {@code null} or an instance of {@link ModelAndView}. When returning a {@link Map},
	 * the {@link Map} instance is wrapped in a new {@link ModelAndView} instance.
	 */
	@SuppressWarnings("unchecked")
	private ModelAndView massageReturnValueIfNecessary(Object returnValue) {
		if (returnValue instanceof ModelAndView) {
			return (ModelAndView) returnValue;
		}
		else if (returnValue instanceof Map) {
			return new ModelAndView().addAllObjects((Map<String, ?>) returnValue);
		}
		else if (returnValue instanceof String) {
			return new ModelAndView((String) returnValue);
		}
		else {
			// Either returned null or was 'void' return.
			// We'll assume that the handle method already wrote the response.
			return null;
		}
	}


	/**
	 * Create a new command object of the given class.
	 * <p>This implementation uses {@code BeanUtils.instantiateClass},
	 * so commands need to have public no-arg constructors.
	 * Subclasses can override this implementation if desired.
	 * @throws Exception if the command object could not be instantiated
	 * @see org.springframework.beans.BeanUtils#instantiateClass(Class)
	 */
	protected Object newCommandObject(Class<?> clazz) throws Exception {
		if (logger.isDebugEnabled()) {
			logger.debug("Creating new command of class [" + clazz.getName() + "]");
		}
		return BeanUtils.instantiateClass(clazz);
	}

	/**
	 * Bind request parameters onto the given command bean
	 * @param request request from which parameters will be bound
	 * @param command command object, that must be a JavaBean
	 * @throws Exception in case of invalid state or arguments
	 */
	protected void bind(HttpServletRequest request, Object command) throws Exception {
		logger.debug("Binding request parameters onto MultiActionController command");
		ServletRequestDataBinder binder = createBinder(request, command);
		binder.bind(request);
		if (this.validators != null) {
			for (Validator validator : this.validators) {
				if (validator.supports(command.getClass())) {
					ValidationUtils.invokeValidator(validator, command, binder.getBindingResult());
				}
			}
		}
		binder.closeNoCatch();
	}

	/**
	 * Create a new binder instance for the given command and request.
	 * <p>Called by {@code bind}. Can be overridden to plug in custom
	 * ServletRequestDataBinder subclasses.
	 * <p>The default implementation creates a standard ServletRequestDataBinder,
	 * and invokes {@code initBinder}. Note that {@code initBinder}
	 * will not be invoked if you override this method!
	 * @param request current HTTP request
	 * @param command the command to bind onto
	 * @return the new binder instance
	 * @throws Exception in case of invalid state or arguments
	 * @see #bind
	 * @see #initBinder
	 */
	protected ServletRequestDataBinder createBinder(HttpServletRequest request, Object command) throws Exception {
		ServletRequestDataBinder binder = new ServletRequestDataBinder(command, getCommandName(command));
		initBinder(request, binder);
		return binder;
	}

	/**
	 * Return the command name to use for the given command object.
	 * <p>Default is "command".
	 * @param command the command object
	 * @return the command name to use
	 * @see #DEFAULT_COMMAND_NAME
	 */
	protected String getCommandName(Object command) {
		return DEFAULT_COMMAND_NAME;
	}

	/**
	 * Initialize the given binder instance, for example with custom editors.
	 * Called by {@code createBinder}.
	 * <p>This method allows you to register custom editors for certain fields of your
	 * command class. For instance, you will be able to transform Date objects into a
	 * String pattern and back, in order to allow your JavaBeans to have Date properties
	 * and still be able to set and display them in an HTML interface.
	 * <p>The default implementation is empty.
	 * <p>Note: the command object is not directly passed to this method, but it's available
	 * via {@link org.springframework.validation.DataBinder#getTarget()}
	 * @param request current HTTP request
	 * @param binder new binder instance
	 * @throws Exception in case of invalid state or arguments
	 * @see #createBinder
	 * @see org.springframework.validation.DataBinder#registerCustomEditor
	 * @see org.springframework.beans.propertyeditors.CustomDateEditor
	 */
	protected void initBinder(HttpServletRequest request, ServletRequestDataBinder binder) throws Exception {
		if (this.webBindingInitializer != null) {
			this.webBindingInitializer.initBinder(binder, new ServletWebRequest(request));
		}
	}


	/**
	 * Determine the exception handler method for the given exception.
	 * <p>Can return {@code null} if not found.
	 * @return a handler for the given exception type, or {@code null}
	 * @param exception the exception to handle
	 */
	protected Method getExceptionHandler(Throwable exception) {
		Class<?> exceptionClass = exception.getClass();
		if (logger.isDebugEnabled()) {
			logger.debug("Trying to find handler for exception class [" + exceptionClass.getName() + "]");
		}
		Method handler = this.exceptionHandlerMap.get(exceptionClass);
		while (handler == null && !exceptionClass.equals(Throwable.class)) {
			if (logger.isDebugEnabled()) {
				logger.debug("Trying to find handler for exception superclass [" + exceptionClass.getName() + "]");
			}
			exceptionClass = exceptionClass.getSuperclass();
			handler = this.exceptionHandlerMap.get(exceptionClass);
		}
		return handler;
	}

	/**
	 * We've encountered an exception thrown from a handler method.
	 * Invoke an appropriate exception handler method, if any.
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @param ex the exception that got thrown
	 * @return a ModelAndView to render the response
	 */
	private ModelAndView handleException(HttpServletRequest request, HttpServletResponse response, Throwable ex)
			throws Exception {

		Method handler = getExceptionHandler(ex);
		if (handler != null) {
			if (logger.isDebugEnabled()) {
				logger.debug("Invoking exception handler [" + handler + "] for exception: " + ex);
			}
			try {
				Object returnValue = handler.invoke(this.delegate, request, response, ex);
				return massageReturnValueIfNecessary(returnValue);
			}
			catch (InvocationTargetException ex2) {
				logger.error("Original exception overridden by exception handling failure", ex);
				ReflectionUtils.rethrowException(ex2.getTargetException());
			}
			catch (Exception ex2) {
				logger.error("Failed to invoke exception handler method", ex2);
			}
		}
		else {
			// If we get here, there was no custom handler or we couldn't invoke it.
			ReflectionUtils.rethrowException(ex);
		}
		throw new IllegalStateException("Should never get here");
	}

}
