/*
    * Copyright 2002-2015 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.util.Collections;
  import java.util.Map;
  import javax.servlet.ServletRequest;
  
  import org.springframework.core.MethodParameter;
  import org.springframework.core.convert.ConversionService;
  import org.springframework.core.convert.TypeDescriptor;
  import org.springframework.core.convert.converter.Converter;
  import org.springframework.util.StringUtils;
  import org.springframework.validation.DataBinder;
  import org.springframework.web.bind.ServletRequestDataBinder;
  import org.springframework.web.bind.WebDataBinder;
  import org.springframework.web.bind.support.WebDataBinderFactory;
  import org.springframework.web.context.request.NativeWebRequest;
  import org.springframework.web.context.request.RequestAttributes;
  import org.springframework.web.method.annotation.ModelAttributeMethodProcessor;
  import org.springframework.web.servlet.HandlerMapping;
  
  /**
   * A Servlet-specific {@link ModelAttributeMethodProcessor} that applies data
   * binding through a WebDataBinder of type {@link ServletRequestDataBinder}.
   *
   * <p>Also adds a fall-back strategy to instantiate the model attribute from a
   * URI template variable or from a request parameter if the name matches the
   * model attribute name and there is an appropriate type conversion strategy.
   *
   * @author Rossen Stoyanchev
   * @since 3.1
   */
  public class ServletModelAttributeMethodProcessor extends ModelAttributeMethodProcessor {
  
  	/**
  	 * @param annotationNotRequired if "true", non-simple method arguments and
  	 * return values are considered model attributes with or without a
  	 * {@code @ModelAttribute} annotation
  	 */
  	public ServletModelAttributeMethodProcessor(boolean annotationNotRequired) {
  		super(annotationNotRequired);
  	}
  
  
  	/**
  	 * Instantiate the model attribute from a URI template variable or from a
  	 * request parameter if the name matches to the model attribute name and
  	 * if there is an appropriate type conversion strategy. If none of these
  	 * are true delegate back to the base class.
  	 * @see #createAttributeFromRequestValue
  	 */
  	@Override
  	protected final Object createAttribute(String attributeName, MethodParameter methodParam,
  			WebDataBinderFactory binderFactory, NativeWebRequest request) throws Exception {
  
  		String value = getRequestValueForAttribute(attributeName, request);
  		if (value != null) {
  			Object attribute = createAttributeFromRequestValue(
  					value, attributeName, methodParam, binderFactory, request);
  			if (attribute != null) {
  				return attribute;
  			}
  		}
  
  		return super.createAttribute(attributeName, methodParam, binderFactory, request);
  	}
  
  	/**
  	 * Obtain a value from the request that may be used to instantiate the
  	 * model attribute through type conversion from String to the target type.
  	 * <p>The default implementation looks for the attribute name to match
  	 * a URI variable first and then a request parameter.
  	 * @param attributeName the model attribute name
  	 * @param request the current request
  	 * @return the request value to try to convert or {@code null}
  	 */
  	protected String getRequestValueForAttribute(String attributeName, NativeWebRequest request) {
  		Map<String, String> variables = getUriTemplateVariables(request);
  		if (StringUtils.hasText(variables.get(attributeName))) {
  			return variables.get(attributeName);
  		}
  		else if (StringUtils.hasText(request.getParameter(attributeName))) {
  			return request.getParameter(attributeName);
  		}
 		else {
 			return null;
 		}
 	}
 
 	@SuppressWarnings("unchecked")
 	protected final Map<String, String> getUriTemplateVariables(NativeWebRequest request) {
 		Map<String, String> variables = (Map<String, String>) request.getAttribute(
 				HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE, RequestAttributes.SCOPE_REQUEST);
 		return (variables != null ? variables : Collections.<String, String>emptyMap());
 	}
 
 	/**
 	 * Create a model attribute from a String request value (e.g. URI template
 	 * variable, request parameter) using type conversion.
 	 * <p>The default implementation converts only if there a registered
 	 * {@link Converter} that can perform the conversion.
 	 * @param sourceValue the source value to create the model attribute from
 	 * @param attributeName the name of the attribute, never {@code null}
 	 * @param methodParam the method parameter
 	 * @param binderFactory for creating WebDataBinder instance
 	 * @param request the current request
 	 * @return the created model attribute, or {@code null}
 	 * @throws Exception
 	 */
 	protected Object createAttributeFromRequestValue(String sourceValue, String attributeName,
 			MethodParameter methodParam, WebDataBinderFactory binderFactory, NativeWebRequest request)
 			throws Exception {
 
 		DataBinder binder = binderFactory.createBinder(request, null, attributeName);
 		ConversionService conversionService = binder.getConversionService();
 		if (conversionService != null) {
 			TypeDescriptor source = TypeDescriptor.valueOf(String.class);
 			TypeDescriptor target = new TypeDescriptor(methodParam);
 			if (conversionService.canConvert(source, target)) {
 				return binder.convertIfNecessary(sourceValue, methodParam.getParameterType(), methodParam);
 			}
 		}
 		return null;
 	}
 
 	/**
 	 * This implementation downcasts {@link WebDataBinder} to
 	 * {@link ServletRequestDataBinder} before binding.
 	 * @see ServletRequestDataBinderFactory
 	 */
 	@Override
 	protected void bindRequestParameters(WebDataBinder binder, NativeWebRequest request) {
 		ServletRequest servletRequest = request.getNativeRequest(ServletRequest.class);
 		ServletRequestDataBinder servletBinder = (ServletRequestDataBinder) binder;
 		servletBinder.bind(servletRequest);
 	}
 
 }