/*
 * Copyright 2004-2008 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.batch.admin.web.freemarker;

import org.springframework.util.StringUtils;
import org.springframework.web.servlet.View;
import org.springframework.web.servlet.ViewResolver;
import org.springframework.web.servlet.support.RequestContextUtils;
import org.springframework.web.servlet.view.freemarker.FreeMarkerView;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.Map;

/**
 * Tiles view implementation that is able to handle partial rendering for Spring
 * Javascript Ajax requests.
 * 
 * <p>
 * On an Ajax request, a "fragments" parameter will be extracted from the request
 * in order to determine which attributes to render from the current view.
 * </p>
 * 
 * @author Dave Syer
 */
public class AjaxFreeMarkerView extends FreeMarkerView {

	/**
	 * Parameter name for the list of fragments top render (value is comma-delimited list).
	 */
	private static final String FRAGMENTS_PARAM = "fragments";

	/**
	 * The accept header value that signifies an Ajax request.
	 */
	private static final String AJAX_ACCEPT_CONTENT_TYPE = "text/html;type=ajax";

	/**
	 * Alternate request parameter to indicate an Ajax request for cases when control of the header is not available.
	 */
	private static final String AJAX_SOURCE_PARAM = "ajaxSource";

	private ViewResolver viewResolver;

	@Override
	public void afterPropertiesSet() throws Exception {
		super.afterPropertiesSet();
	}

	public void setViewResolver(ViewResolver viewResolver) {
		this.viewResolver = viewResolver;
	}

	protected void renderMergedTemplateModel(Map<String, Object> model, HttpServletRequest request,
			HttpServletResponse response) throws Exception {

		if (isAjaxRequest(request, response)) {

			String[] attrNames = getRenderFragments(model, request, response);
			if (attrNames.length == 0) {
				logger.warn("An Ajax request was detected, but no fragments were specified to be re-rendered.  "
						+ "Falling back to full page render.");
				super.renderMergedTemplateModel(model, request, response);
			}

			// initialize the session before rendering any fragments. Otherwise
			// views that require the session which has
			// not otherwise been initialized will fail to render
			request.getSession();
			response.flushBuffer();
			for (int i = 0; i < attrNames.length; i++) {
				View fragmentView = null;

				try {
					fragmentView = (View) getApplicationContext().getBean(attrNames[i], View.class);
				}
				catch (Exception e) {
					if (getAttributesMap().containsKey(attrNames[i])) {
						String viewName = (String) getAttributesMap().get(attrNames[i]);
						fragmentView = viewResolver.resolveViewName(viewName, RequestContextUtils.getLocale(request));
					}
				}

				if (fragmentView == null) {
					throw new ServletException("No View with a name of '" + attrNames[i] + "' could be found: " + this);
				}
				else {
					fragmentView.render(model, request, response);
				}
			}
		}
		else {
			super.renderMergedTemplateModel(model, request, response);
		}
	}

	protected boolean isAjaxRequest(HttpServletRequest request, HttpServletResponse response) {
		String acceptHeader = request.getHeader("Accept");
		String ajaxParam = request.getParameter(AJAX_SOURCE_PARAM);
		if (AJAX_ACCEPT_CONTENT_TYPE.equals(acceptHeader) || StringUtils.hasText(ajaxParam)) {
			return true;
		} else {
			return false;
		}
	}
	protected String[] getRenderFragments(Map<String, Object> model, HttpServletRequest request,
			HttpServletResponse response) {
		String attrName = request.getParameter(FRAGMENTS_PARAM);
		String[] renderFragments = StringUtils.commaDelimitedListToStringArray(attrName);
		return StringUtils.trimArrayElements(renderFragments);
	}

}