/*
    * Copyright 2002-2013 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.messaging.handler.annotation.support;
  
  import java.lang.reflect.Method;
  import java.util.Map;
  
  import org.springframework.core.MethodParameter;
  import org.springframework.messaging.Message;
  import org.springframework.messaging.MessageHeaders;
  import org.springframework.messaging.handler.annotation.Header;
  import org.springframework.messaging.handler.annotation.Headers;
  import org.springframework.messaging.handler.invocation.HandlerMethodArgumentResolver;
  import org.springframework.messaging.support.MessageHeaderAccessor;
  import org.springframework.util.Assert;
  import org.springframework.util.ReflectionUtils;
  
  /**
   * Resolves the following method parameters:
   * <ul>
   * <li>Parameters assignable to {@link Map} annotated with {@link Header @Headers}
   * <li>Parameters of type {@link MessageHeaders}
   * <li>Parameters assignable to {@link MessageHeaderAccessor}
   * </ul>
   *
   * @author Rossen Stoyanchev
   * @since 4.0
   */
  public class HeadersMethodArgumentResolver implements HandlerMethodArgumentResolver {
  
  	@Override
  	public boolean supportsParameter(MethodParameter parameter) {
  		Class<?> paramType = parameter.getParameterType();
  		return ((parameter.hasParameterAnnotation(Headers.class) && Map.class.isAssignableFrom(paramType)) ||
  				MessageHeaders.class.equals(paramType) ||
  				MessageHeaderAccessor.class.isAssignableFrom(paramType));
  	}
  
  	@Override
  	public Object resolveArgument(MethodParameter parameter, Message<?> message) throws Exception {
  
  		Class<?> paramType = parameter.getParameterType();
  
  		if (Map.class.isAssignableFrom(paramType)) {
  			return message.getHeaders();
  		}
  		else if (MessageHeaderAccessor.class.equals(paramType)) {
  			MessageHeaderAccessor accessor = MessageHeaderAccessor.getAccessor(message, MessageHeaderAccessor.class);
  			return (accessor != null ? accessor : new MessageHeaderAccessor(message));
  		}
  		else if (MessageHeaderAccessor.class.isAssignableFrom(paramType)) {
  			MessageHeaderAccessor accessor = MessageHeaderAccessor.getAccessor(message, MessageHeaderAccessor.class);
  			if (accessor != null && paramType.isAssignableFrom(accessor.getClass())) {
  				return accessor;
  			}
  			else {
  				Method method = ReflectionUtils.findMethod(paramType, "wrap", Message.class);
  				Assert.notNull(method, "Cannot create accessor of type " + paramType + " for message " +  message);
  				return ReflectionUtils.invokeMethod(method, null, message);
  			}
  		}
  		else {
  			throw new IllegalStateException(
  					"Unexpected method parameter type " + paramType + "in method " + parameter.getMethod() + ". "
  					+ "@Headers method arguments must be assignable to java.util.Map.");
  		}
  	}
  
  }