import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;
import java.util.Date;
import java.util.Dictionary;

import org.xml.sax.EntityResolver;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

// ASSUMES:  this shares a package with a "Storage" class
// that at least maps keys to data. 

/**
 * Entity Resolver, with Chaining
 */
public class MyResolver implements EntityResolver
{
    private EntityResolver next;
    private Dictionary     map;

    // n -- optional resolver to consult on failure 
    // m -- mapping public ids to preferred URLs
    public MyResolver (EntityResolver n, Dictionary m)
	{ next = n; map = m; }

    public InputSource resolveEntity (String publicId, String systemId)
    throws SAXException, IOException
    {
	// magic URL?
	if ("http://localhost/xml/date".equals (systemId)) {
	    InputSource	  retval = new InputSource (systemId);
	    Reader 	  date;

	    date = new StringReader (new Date().toString ());
	    retval.setCharacterStream (date);
	    return retval;
	}

	// nonstandard URI scheme?
	if (systemId.startsWith ("blob:")) {
	    InputSource	  retval = new InputSource (systemId);
	    String        key = systemId.substring (5);
	    byte          data [] = Storage.keyToBlob (key);

	    retval.setByteStream (new ByteArrayInputStream (data));
	    return retval;
	}

	// use table to map public id to local URL?
	if (map != null && publicId != null) {
	    String url = (String) map.get (publicId);
	    if (url != null)
		return new InputSource (url);
	}

	// chain to next resolver?
	if (next != null)
	    return next.resolveEntity (publicId, systemId);
	return null;
    }
}