/*
    * Copyright 2002-2014 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.servlet.view.groovy;
  
  import java.io.BufferedWriter;
  import java.io.IOException;
  import java.util.Locale;
  import java.util.Map;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  import groovy.text.Template;
  import groovy.text.markup.MarkupTemplateEngine;
  
  import org.springframework.beans.BeansException;
  import org.springframework.beans.factory.BeanFactoryUtils;
  import org.springframework.beans.factory.NoSuchBeanDefinitionException;
  import org.springframework.context.ApplicationContext;
  import org.springframework.context.ApplicationContextException;
  import org.springframework.web.servlet.view.AbstractTemplateView;
  import org.springframework.web.util.NestedServletException;
  
  /**
   * An {@link org.springframework.web.servlet.view.AbstractTemplateView AbstractTemplateView}
   * based on Groovy XML/XHTML markup templates.
   *
   * <p>Spring's Groovy Markup Template support requires Groovy 2.3.1 and higher.
   *
   * @author Brian Clozel
   * @author Rossen Stoyanchev
   * @since 4.1
   * @see GroovyMarkupViewResolver
   * @see GroovyMarkupConfigurer
   * @see <a href="http://beta.groovy-lang.org/docs/groovy-2.3.2/html/documentation/markup-template-engine.html">
   *     Groovy Markup Template engine documentation</a>
   */
  public class GroovyMarkupView extends AbstractTemplateView {
  
  	private MarkupTemplateEngine engine;
  
  
  	/**
  	 * Set the MarkupTemplateEngine to use in this view.
  	 * <p>If not set, the engine is auto-detected by looking up up a single
  	 * {@link GroovyMarkupConfig} bean in the web application context and using
  	 * it to obtain the configured {@code MarkupTemplateEngine} instance.
  	 * @see GroovyMarkupConfig
  	 */
  	public void setTemplateEngine(MarkupTemplateEngine engine) {
  		this.engine = engine;
  	}
  
  	@Override
  	public boolean checkResource(Locale locale) throws Exception {
  		try {
  			this.engine.resolveTemplate(getUrl());
  		}
  		catch (IOException exception) {
  			return false;
  		}
  		return true;
  	}
  
  	/**
  	 * Invoked at startup.
  	 * If no {@link #setTemplateEngine(MarkupTemplateEngine) templateEngine} has
  	 * been manually set, this method looks up a {@link GroovyMarkupConfig} bean
  	 * by type and uses it to obtain the Groovy Markup template engine.
  	 * @see GroovyMarkupConfig
  	 * @see #setTemplateEngine(groovy.text.markup.MarkupTemplateEngine)
  	 */
  	@Override
  	protected void initApplicationContext(ApplicationContext context) {
  		super.initApplicationContext();
  		if (this.engine == null) {
  			setTemplateEngine(autodetectMarkupTemplateEngine());
  		}
  	}
  
  	/**
  	 * Autodetect a MarkupTemplateEngine via the ApplicationContext.
  	 * Called if a MarkupTemplateEngine has not been manually configured.
  	 */
  	protected MarkupTemplateEngine autodetectMarkupTemplateEngine() throws BeansException {
  		try {
 			return BeanFactoryUtils.beanOfTypeIncludingAncestors(getApplicationContext(),
 					GroovyMarkupConfig.class, true, false).getTemplateEngine();
 		}
 		catch (NoSuchBeanDefinitionException ex) {
 			throw new ApplicationContextException("Expected a single GroovyMarkupConfig bean in the current " +
 					"Servlet web application context or the parent root context: GroovyMarkupConfigurer is " +
 					"the usual implementation. This bean may have any name.", ex);
 		}
 	}
 
 
 	@Override
 	protected void renderMergedTemplateModel(Map<String, Object> model,
 			HttpServletRequest request, HttpServletResponse response) throws Exception {
 
 		Template template = getTemplate(getUrl());
 		template.make(model).writeTo(new BufferedWriter(response.getWriter()));
 	}
 
 	/**
 	 * Return a template compiled by the configured Groovy Markup template engine
 	 * for the given view URL.
 	 */
 	protected Template getTemplate(String viewUrl) throws Exception {
 		try {
 			return this.engine.createTemplateByPath(viewUrl);
 		}
 		catch (ClassNotFoundException ex) {
 			Throwable cause = (ex.getCause() != null ? ex.getCause() : ex);
 			throw new NestedServletException("Could not find class while rendering Groovy Markup view with name '" +
 					getUrl() + "': " + ex.getMessage() +  "'", cause);
 		}
 	}
 
 }