/*
 * Copyright 2002-2018 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
 *
 *      https://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;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.core.Ordered;
import org.springframework.lang.Nullable;
import org.springframework.web.method.HandlerMethod;
import org.springframework.web.servlet.HandlerAdapter;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.support.WebContentGenerator;

/**
 * Abstract base class for {@link HandlerAdapter} implementations that support
 * handlers of type {@link HandlerMethod}.
 *
 * @author Arjen Poutsma
 * @since 3.1
 */
public abstract class AbstractHandlerMethodAdapter extends WebContentGenerator implements HandlerAdapter, Ordered {

	private int order = Ordered.LOWEST_PRECEDENCE;


	public AbstractHandlerMethodAdapter() {
		// no restriction of HTTP methods by default
		super(false);
	}


	/**
	 * Specify the order value for this HandlerAdapter bean.
	 * <p>The default value is {@code Ordered.LOWEST_PRECEDENCE}, meaning non-ordered.
	 * @see org.springframework.core.Ordered#getOrder()
	 */
	public void setOrder(int order) {
		this.order = order;
	}

	@Override
	public int getOrder() {
		return this.order;
	}


	/**
	 * 方法实现说明:我们的handlerAdapter是否支持当前的handler
	 * @author:smlz
	 * @param handler
	 * @return:
	 * @exception:
	 * @date:2019/8/11 16:20
	 */
	@Override
	public final boolean supports(Object handler) {
		//判断hanlder 是不是HandlerMethod实现类或者子类   && 默认返回true
		return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler));
	}

	/**
	 * Given a handler method, return whether or not this adapter can support it.
	 * @param handlerMethod the handler method to check
	 * @return whether or not this adapter can adapt the given method
	 */
	protected abstract boolean supportsInternal(HandlerMethod handlerMethod);

	/**
	 * 方法实现说明:父类中获取我们的ModleAndView对象
	 * @author:smlz
	 * @param request
	 * @param response
	 * @param handler
	 * @return:ModelAndView
	 * @exception:
	 * @date:2019/8/11 17:16
	 */
	@Override
	@Nullable
	public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
			throws Exception {

		/**
		 * 调用到具体子类的方法
		 */
		return handleInternal(request, response, (HandlerMethod) handler);
	}

	/**
	 * Use the given handler method to handle the request.
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @param handlerMethod handler method to use. This object must have previously been passed to the
	 * {@link #supportsInternal(HandlerMethod)} this interface, which must have returned {@code true}.
	 * @return ModelAndView object with the name of the view and the required model data,
	 * or {@code null} if the request has been handled directly
	 * @throws Exception in case of errors
	 */
	@Nullable
	protected abstract ModelAndView handleInternal(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception;

	/**
	 * This implementation expects the handler to be an {@link HandlerMethod}.
	 */
	@Override
	public final long getLastModified(HttpServletRequest request, Object handler) {
		return getLastModifiedInternal(request, (HandlerMethod) handler);
	}

	/**
	 * Same contract as for {@link javax.servlet.http.HttpServlet#getLastModified(HttpServletRequest)}.
	 * @param request current HTTP request
	 * @param handlerMethod handler method to use
	 * @return the lastModified value for the given handler
	 */
	protected abstract long getLastModifiedInternal(HttpServletRequest request, HandlerMethod handlerMethod);

}
