package org.freehep.util.template;

import java.io.FilterReader;
import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

/** A very simple template engine. The template engine takes input and transforms
 * it by looking for tags in the document, and replacing them with values provided
 * by a set of ValueProviders.
 * 

 * Example of HTML template:

 *  <html>

 * <head>

 * <title>{v:title}</title> 

 * </head> 

 * <body>

 * Welcome {v:name} to Simple Template Example

 * <table>

 * <tr bgcolor="d0d0d0"><th>Author</th><th>Title</th><th>Year</th></tr>

 * <t:book>

 * <tr>

 * <td><a href="#">{v:author}</a></td>

 * <td><a href="#">{v:title}</a></td>

 * <td><a href="#">{v:year}</a></td>

 * </tr>

 * </t:book>

 * </table>

 * </body> 

 * </html> 
 * 

 * The design (although not the code) was inspired by the JByte template engine
 * @link {http://javaby.sourceforge.net/}.
 * @author tonyj
 * @version $Id: TemplateEngine.java 8584 2006-08-10 23:06:37Z duns $
 */
public class TemplateEngine
{
   /** Apply the template to a document.
    * @param in The Reader from which the document will be read.
    * @return A Reader from which the filtered document can be read.
    */
   public Reader filter(Reader in)
   {
      return new TemplateReader(in,providers);
   }

   /** Add a value provider to the set of value providers
    * @param p The ValueProvider to add
    */
   public void addValueProvider(ValueProvider p)
   {
      providers.add(p);
   }
   /** Remove a value provider from the list of value providers.
    * @param p The value provider to remove.
    */
   public void removeValueProvider(ValueProvider p)
   {
      providers.remove(p);
   }
   private List providers = new ArrayList();
   private static class TemplateReader extends FilterReader
   {
      TemplateReader(Reader in, List providers)
      {
         super(in);
         this.providers = providers;
      }

      public int read() throws IOException
      {
         outer: for (;;)
         {
            if (subReader != null)
            {
               int c = subReader.read();
               if (c >= 0) return c;
               subReader = null;
            }

            if (templateIterator != null)
            {
               if (templateIterator.hasNext())
               {
                  ValueProvider vp = (ValueProvider) templateIterator.next();
                  subReader = new TemplateReader(new StringReader(buf.toString()),Collections.singletonList(vp));
                  continue;
               }
               else
               {
                  templateIterator = null;
                  buf.delete(0, buf.length());
               }
            }

            if (state < 0)
            {
               int rc = buf.charAt(buf.length()+state++);
               if (state == 0) buf.delete(0,buf.length());
               return rc;
            }


            int c = in.read();
            if (c<0)
            {
               state = -buf.length();
               if (state == 0) return -1;
               continue;
            }

            if (templateMarker > 0)
            {
               buf.append((char) c);
               if      (state == 0 && c == '<') state++;
               else if (state == 1 && c == '/') state++;
               else if (state > 1 && buf.charAt(state-1) == c) state++;
               else state = 0;
               if (state-1 == templateMarker) // Found end of template
               {
                  String symb = buf.substring(3,templateMarker-1);
                  for (int i=0; i 2 && (template ? c!='>' : c!='}'))
            {
               state++;
               buf.append((char) c);
            }
            else if (state > 2)
            {
               if (template)
               {
                  // Everything must go into the string buffer until we
                  // find end of template
                  buf.append((char) c);
                  state++;
                  templateMarker = state;
                  state = 0;
               }
               else
               {
                  String symb = buf.substring(3);
                  for (int i=0; i