/*
    * Copyright 2002-2014 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.method.annotation;
  
  import java.lang.reflect.Method;
  import java.util.List;
  
  import org.springframework.core.MethodParameter;
  import org.springframework.ui.ExtendedModelMap;
  import org.springframework.web.context.request.NativeWebRequest;
  import org.springframework.web.method.annotation.ModelAttributeMethodProcessor;
  import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
  import org.springframework.web.method.support.ModelAndViewContainer;
  import org.springframework.web.servlet.ModelAndView;
  import org.springframework.web.servlet.mvc.annotation.ModelAndViewResolver;
  
  /**
   * This return value handler is intended to be ordered after all others as it
   * attempts to handle _any_ return value type (i.e. returns {@code true} for
   * all return types).
   *
   * <p>The return value is handled either with a {@link ModelAndViewResolver}
   * or otherwise by regarding it as a model attribute if it is a non-simple
   * type. If neither of these succeeds (essentially simple type other than
   * String), {@link UnsupportedOperationException} is raised.
   *
   * <p><strong>Note:</strong> This class is primarily needed to support
   * {@link ModelAndViewResolver}, which unfortunately cannot be properly
   * adapted to the {@link HandlerMethodReturnValueHandler} contract since the
   * {@link HandlerMethodReturnValueHandler#supportsReturnType} method
   * cannot be implemented. Hence {@code ModelAndViewResolver}s are limited
   * to always being invoked at the end after all other return value
   * handlers have been given a chance. It is recommended to re-implement
   * a {@code ModelAndViewResolver} as {@code HandlerMethodReturnValueHandler},
   * which also provides better access to the return type and method information.
   *
   * @author Rossen Stoyanchev
   * @since 3.1
   */
  public class ModelAndViewResolverMethodReturnValueHandler implements HandlerMethodReturnValueHandler {
  
  	private final List<ModelAndViewResolver> mavResolvers;
  
  	private final ModelAttributeMethodProcessor modelAttributeProcessor = new ModelAttributeMethodProcessor(true);
  
  
  	/**
  	 * Create a new instance.
  	 */
  	public ModelAndViewResolverMethodReturnValueHandler(List<ModelAndViewResolver> mavResolvers) {
  		this.mavResolvers = mavResolvers;
  	}
  
  
  	/**
  	 * Always returns {@code true}. See class-level note.
  	 */
  	@Override
  	public boolean supportsReturnType(MethodParameter returnType) {
  		return true;
  	}
  
  	@Override
  	public void handleReturnValue(Object returnValue, MethodParameter returnType,
  			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
  
  		if (this.mavResolvers != null) {
  			for (ModelAndViewResolver mavResolver : this.mavResolvers) {
  				Class<?> handlerType = returnType.getContainingClass();
  				Method method = returnType.getMethod();
  				ExtendedModelMap model = (ExtendedModelMap) mavContainer.getModel();
  				ModelAndView mav = mavResolver.resolveModelAndView(method, handlerType, returnValue, model, webRequest);
  				if (mav != ModelAndViewResolver.UNRESOLVED) {
  					mavContainer.addAllAttributes(mav.getModel());
  					mavContainer.setViewName(mav.getViewName());
  					if (!mav.isReference()) {
  						mavContainer.setView(mav.getView());
  					}
  					return;
  				}
  			}
  		}
  
  		// No suitable ModelAndViewResolver...
  		if (this.modelAttributeProcessor.supportsReturnType(returnType)) {
 			this.modelAttributeProcessor.handleReturnValue(returnValue, returnType, mavContainer, webRequest);
 		}
 		else {
 			throw new UnsupportedOperationException("Unexpected return type: " +
 					returnType.getParameterType().getName() + " in method: " + returnType.getMethod());
 		}
 	}
 
 }