/*
    * $Source$
    * $Revision$
    *
    * Copyright (C) 2000 Tim Joyce
    *
    * Part of Melati (http://melati.org), a framework for the rapid
    * development of clean, maintainable web applications.
    *
   * Melati is free software; Permission is granted to copy, distribute
   * and/or modify this software under the terms either:
   *
   * a) the GNU General Public License as published by the Free Software
   *    Foundation; either version 2 of the License, or (at your option)
   *    any later version,
   *
   *    or
   *
   * b) any version of the Melati Software License, as published
   *    at http://melati.org
   *
   * You should have received a copy of the GNU General Public License and
   * the Melati Software License along with this program;
   * if not, write to the Free Software Foundation, Inc.,
   * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA to obtain the
   * GNU General Public License and visit http://melati.org to obtain the
   * Melati Software License.
   *
   * Feel free to contact the Developers of Melati (http://melati.org),
   * if you would like to work out a different arrangement than the options
   * outlined here.  It is our intention to allow Melati to be used by as
   * wide an audience as possible.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * Contact details for copyright holder:
   *
   *     Tim Joyce <timj At paneris.org>
   */
  
  package org.melati.template.velocity;
  
  import java.util.Properties;
  
  import org.melati.MelatiConfig;
  import org.melati.poem.AccessPoemException;
  import org.melati.template.AbstractTemplateEngine;
  import org.melati.template.TemplateContext;
  import org.melati.template.TemplateEngine;
  import org.melati.template.TemplateEngineException;
  import org.melati.template.NotFoundException;
  import org.melati.util.MelatiBugMelatiException;
  import org.melati.util.MelatiStringWriter;
  import org.melati.util.MelatiWriter;
  
  import org.apache.velocity.VelocityContext;
  import org.apache.velocity.app.Velocity;
  import org.apache.velocity.exception.MethodInvocationException;
  import org.apache.velocity.exception.ParseErrorException;
  import org.apache.velocity.exception.ResourceNotFoundException;
  
  /**
   * Wrapper for the Velocity Template Engine for use with Melati.
   */
  public class VelocityTemplateEngine extends AbstractTemplateEngine implements
      TemplateEngine {
  
    /** The name of the engine. */
    public static final String NAME = "velocity";
  
    /**
     * This is the string that is looked for when getInitParameter is called.
     */
    // private static final String INIT_PROPS_KEY = "velocity.properties";
    /**
     * Constructor.
     */
    public VelocityTemplateEngine() {
      super();
    }
  
    /**
     * Construct a new Engine.
     * 
     * @param melatiConfig
     *        a {@link MelatiConfig}
     * @throws TemplateEngineException
     *         if any problem occurs with the engine
     */
    public void init(MelatiConfig melatiConfig)
        throws TemplateEngineException {
      try {
        Properties props = loadConfiguration();
        Velocity.init(props);
      } catch (Exception e) {
        throw new TemplateEngineException(e);
     }
   }
 
 
   protected Properties loadConfiguration() {
     Properties p = new Properties();
     p.setProperty("resource.loader", "class");
     p.setProperty("class.resource.loader.class",
         WebMacroClasspathResourceLoader.class.getName());
     return p;
   }
 
   /**
    * Get the template context for Velocity.
    * 
    * @return a {@link TemplateContext}
    */
   public TemplateContext getTemplateContext() {
     VelocityContext context = new VelocityContext();
     return new VelocityServletTemplateContext(context);
   }
 
   /**
    * The name of the template engine (used to find the templets).
    * 
    * @return the name of the current configured template engine
    */
   @Override
   public String getName() {
     return NAME;
   }
 
   /**
    * @return the extension of the templates used by Velocity, including the dot.
    */
   @Override
   public String templateExtension() {
     return ".vm";
   }
 
   /**
    * Get a template by name.
    * 
    * @param templateName
    *        the name of the template to find
    * @return a template
    * @throws NotFoundException if template not found
    */
   @Override
   public org.melati.template.Template template(String templateName)
       throws NotFoundException {
     try {
       return new VelocityTemplate(templateName);
     } catch (ResourceNotFoundException e) {
       if (templateName.endsWith(templateExtension())) {
         // have a go at loading the webmacro template, and converting it!
         String webmacroTemplateName = templateName.substring(0, templateName
             .lastIndexOf(templateExtension()))
             + ".wm";
         try {
           return new VelocityTemplate(webmacroTemplateName);
         } catch (ParseErrorException p) {
           throw new MelatiBugMelatiException(
               "Problem converting a WebMacro template to a Velocity template: " + webmacroTemplateName,
               p);
         } catch (ResourceNotFoundException e2) {
             throw new NotFoundException("Could not find template " + templateName + " or " + webmacroTemplateName);
         } 
       } else throw new NotFoundException("Could not find template " + templateName);
     } catch (Exception e) {
       throw new TemplateEngineException(e);
     }
   }
 
   /**
    * Get a Template by name and expand it against a context.
    * 
    * @param out
    *        a {@link MelatiWriter} to output on
    * @param templateName
    *        the name of the template to expand
    * @param templateContext
    *        the {@link TemplateContext} to expand the template against
    * @throws NotFoundException if template not found
    */
   public void expandTemplate(MelatiWriter out, String templateName,
       TemplateContext templateContext) throws NotFoundException {
     expandTemplate(out, template(templateName), templateContext);
   }
 
   /**
    * Expand a {@link org.melati.template.Template} against the context.
    * 
    * @param out
    *        a {@link MelatiWriter} to output on
    * @param template
    *        the {@link org.melati.template.Template} to expand
    * @param templateContext
    *        the {@link TemplateContext} to expand the template against
    * @see org.melati.template.TemplateEngine#expandTemplate(org.melati.util.MelatiWriter, org.melati.template.Template, org.melati.template.TemplateContext)
    */
   @Override
   public void expandTemplate(MelatiWriter out,
       org.melati.template.Template template, TemplateContext templateContext) {
     try {
       template.write(out, templateContext);
     } catch (TemplateEngineException problem) {
       Exception underlying = problem.subException;
       if (underlying instanceof AccessPoemException) {
         throw (AccessPoemException)underlying;
       }
       if (underlying instanceof MethodInvocationException) {
         Throwable caught = ((MethodInvocationException)underlying)
             .getWrappedThrowable();
         if (caught instanceof AccessPoemException) {
           throw (AccessPoemException)caught;
         }
       }
       throw problem;
     } 
 
   }
 
   /**
    * @see org.melati.template.TemplateEngine#expandedTemplate(org.melati.template.Template, org.melati.template.TemplateContext)
    */
   @Override
   public String expandedTemplate(org.melati.template.Template template,
       TemplateContext templateContext) {
     MelatiStringWriter s = new MelatiStringWriter();
     expandTemplate(s, template, templateContext);
     return s.toString();
   }
 
   /**
    * @see org.melati.template.TemplateEngine#getStringWriter()
    */
   @Override
   public MelatiStringWriter getStringWriter() {
     return new MelatiStringWriter();
   }
 
   /**
    * Get the underlying engine.
    * 
    * @see org.melati.template.TemplateEngine#getEngine()
    * @return null - for velocity there is none.
    */
   @Override
   public Object getEngine() {
     return null;
   }
 
 }