/*
    * $Source: /usr/cvsroot/melati/melati/src/main/java/org/melati/template/TemplateEngine.java,v $
    * $Revision: 1.38 $
    *
    * Copyright (C) 2005 Tim Pizey
    *
    * 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 Pizey <timp At paneris.org>
   *     http://paneris.org/~timp
   */
  package org.melati.template;
  
  import java.io.IOException;
  import java.util.Enumeration;
  
  import org.melati.Melati;
  import org.melati.MelatiConfig;
  import org.melati.util.MelatiStringWriter;
  import org.melati.util.MelatiWriter;
  
  /**
   * A TemplateEngine typically evaluates a template containing variables 
   * against a context containing values for those variables.
   * 
   * The canonical java Template Engines are WebMacro and Velocity.
   * 
   * @author timp At paneris.org
   */
  public interface TemplateEngine {
    
    /**
     * Initialise the Engine.
     *
     * @param melatiConfig a {@link MelatiConfig}
     * @throws TemplateEngineException if any problem occurs with the engine
     */
    void init(MelatiConfig melatiConfig) throws TemplateEngineException;
  
    /**
     * Create a new Context for this engine.
     *
     * @param melati the {@link Melati}
     * @throws TemplateEngineException if any problem occurs with the engine
     * @return a {@link TemplateContext}
     */
    TemplateContext getTemplateContext(Melati melati)
        throws TemplateEngineException;
  
    /**
     * The name of the template engine (used to find the templets).
     * @return the name of the current configured template engine
     */
    String getName();
  
    /**
     * @return the extension of the templates used by this template engine,
     * including the dot.
     */
    String templateExtension();
  
    /**
     * A root should not end in a slash.
     * 
     * @return an Enumeration of string roots, always at least the empty string
     */
    Enumeration getRoots();
   
   /**
    * Add a template root directory.
    * NOTE A root should not start or end in a slash.
    * 
    * @param root the root to add
    */
   void addRoot(String root);
   
   /** 
    * Get a template given it's full name.
    * 
    * @param templateName the name of the template to find
    * @throws IOException if TemplateEngine does
    * @throws NotFoundException if template not found
    * @return a template
    */
   Template template(String templateName) 
     throws IOException, NotFoundException;
 
   /**
    * The name of a template which exists.
    * 
    * @param key short name, without path or extension
    * @param classifier a purpose or database name or similar qualifier 
    * @return the name of a template, null if none found
    */
   String getTemplateName(String key, String classifier);
    
   /** 
    * Expand the Template against the context.
    *
    * @param out             a {@link MelatiWriter} to output on
    * @param templateName    the name of the template to expand
    * @param templateContext the {@link ServletTemplateContext} to expand 
    *                        the template against
    * @throws IOException if TemplateEngine does
    * @throws NotFoundException if template not found
    */
   void expandTemplate(MelatiWriter out, String templateName,
       TemplateContext templateContext) throws IOException, NotFoundException;
 
   /** 
    * Expand the Template against the context.
    *
    * @param out             a {@link MelatiWriter} to output on
    * @param template        the {@link Template} to expand
    * @param templateContext the {@link ServletTemplateContext} to expand 
    *                        the template against
    * @throws IOException if TemplateEngine does
    */
   void expandTemplate(MelatiWriter out, Template template,
       TemplateContext templateContext) throws IOException;
 
   /** 
    * Expand the Template against the context and return the expansion as a string.
    *
    * @param template        the {@link Template} to expand
    * @param templateContext the {@link ServletTemplateContext} to expand 
    *                        the template against
    * @return the interpolated template as a String
    * @throws IOException if TemplateEngine does
    */
   String expandedTemplate(Template template, TemplateContext templateContext)
       throws IOException;
 
   /** 
    * @return a {@link MelatiStringWriter}.
    * @see Melati#getStringWriter() 
    */
   MelatiStringWriter getStringWriter();
 
   /** 
    * Get the underlying engine.
    *
    * @return the configured template engine
    */
   Object getEngine();
 
 }