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/*===========================================================================
  Copyright (C) 2008-2009 by the Okapi Framework contributors
-----------------------------------------------------------------------------
  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 net.sf.okapi.common;

import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Iterator;

import javax.xml.XMLConstants;
import javax.xml.namespace.NamespaceContext;

/**
 * Helper class to manage XML namespaces.
 * The reserved xml and xmlns prefixes are hard-coded.
 * The following namespaces are pre-defined:
 * 
xml : http://www.w3.org/XML/1998/namespace
 * xmlns : http://www.w3.org/2000/xmlns/
 * xsl : http://www.w3.org/1999/XSL/Transform
 * 
 */
public class NSContextManager implements NamespaceContext {

	private Hashtable table;
	
	/**
	 * Creates a new NSContextManager object.
	 */
	public NSContextManager () {
		table = new Hashtable<>();
		// Defaults in addition to the hard-coded
		add("xsl", "http://www.w3.org/1999/XSL/Transform");
	}
	
	/**
	 * Gets the namespace URI for a given prefix.
	 * @param prefix The prefix to look up.
	 * @return The namespace URI for the given prefix, or XMLConstants.NULL_NS_URI if none was found. 
	 */
	public String getNamespaceURI (String prefix) {
		if ( table.containsKey(prefix) )
			return table.get(prefix);
		if ( prefix.equals(XMLConstants.XML_NS_PREFIX) )
			return XMLConstants.XML_NS_URI;
		if ( prefix.equals(XMLConstants.XMLNS_ATTRIBUTE) )
			return XMLConstants.XMLNS_ATTRIBUTE_NS_URI;
		// Default
		return XMLConstants.NULL_NS_URI;
	}

	/**
	 * Gets the prefix for a given namespace URI.
	 * @param uri The namespace URI to look up.
	 * @return The prefix for the given namespace URI, or null the mamager has no such
	 * namespace URI defined.
	 */
	public String getPrefix (String uri) {
		Enumeration E = table.keys();
		String key;
		while ( E.hasMoreElements() ) {
			key = E.nextElement();
			if ( table.get(key).equals(uri) )
				return key;
		}
		if ( uri.equals(XMLConstants.XML_NS_URI))
			return XMLConstants.XML_NS_PREFIX;
		if ( uri.equals(XMLConstants.XMLNS_ATTRIBUTE_NS_URI) )
			return XMLConstants.XMLNS_ATTRIBUTE;
		else
			return null;
	}

	/**
	 * Not implemented.
	 * @return Always null.
	 */
	public Iterator getPrefixes (String uri) {
		// Not implemented
		return null;
	} 

	/**
	 * Adds a prefix/uri pair to the manager. No checking is done for existing
	 * prefix: If the same is already defined, it will be overwritten.
	 * @param prefix The prefix of the namespace
	 * @param uri The uri of the namespace
	 */
	public void add (String prefix,
		String uri) {
		table.put(prefix, uri);
	}

}