/*
    * 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);
 	}
 
 }