/*
 * Copyright 2002-2017 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.method.annotation;

import org.springframework.core.MethodParameter;
import org.springframework.lang.Nullable;
import org.springframework.ui.Model;
import org.springframework.util.Assert;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
import org.springframework.web.method.support.ModelAndViewContainer;

Resolves Model arguments and handles Model return values. 
A Model return type has a set purpose. Therefore this handler should be configured ahead of handlers that support any return value type annotated with @ModelAttribute or @ResponseBody to ensure they don't take over. 
Author:
Rossen Stoyanchev
Since:
3.1/**
 * Resolves {@link Model} arguments and handles {@link Model} return values.
 *
 * <p>A {@link Model} return type has a set purpose. Therefore this handler
 * should be configured ahead of handlers that support any return value type
 * annotated with {@code @ModelAttribute} or {@code @ResponseBody} to ensure
 * they don't take over.
 *
 * @author Rossen Stoyanchev
 * @since 3.1
 */
public class ModelMethodProcessor implements HandlerMethodArgumentResolver, HandlerMethodReturnValueHandler {

	@Override
	public boolean supportsParameter(MethodParameter parameter) {
		return Model.class.isAssignableFrom(parameter.getParameterType());
	}

	@Override
	@Nullable
	public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {

		Assert.state(mavContainer != null, "ModelAndViewContainer is required for model exposure");
		return mavContainer.getModel();
	}

	@Override
	public boolean supportsReturnType(MethodParameter returnType) {
		return Model.class.isAssignableFrom(returnType.getParameterType());
	}

	@Override
	public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {

		if (returnValue == null) {
			return;
		}
		else if (returnValue instanceof Model) {
			mavContainer.addAllAttributes(((Model) returnValue).asMap());
		}
		else {
			// should not happen
			throw new UnsupportedOperationException("Unexpected return type: " +
					returnType.getParameterType().getName() + " in method: " + returnType.getMethod());
		}
	}

}