// Namespaces.java - Analyze namespace nodes in a DOM tree

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package org.apache.xml.resolver.helpers;

import org.w3c.dom.*;

/**
 * Static Namespace query methods.
 *
 * <p>This class defines a set of static methods that can be called
 * to analyze the namespace properties of DOM nodes.</p>
 *
 * @author Norman Walsh
 * <a href="mailto:Norman.Walsh@Sun.COM">Norman.Walsh@Sun.COM</a>
 *
 * @version 1.0
 */
public class Namespaces {
    /**
     * Returns the "prefix" part of a QName or the empty string (not
     * null) if the name has no prefix.
     *
     * @param element The QName of an element.
     * @return The prefix part of the element name.
     */
    public static String getPrefix(Element element) {
	String name = element.getTagName();
	String prefix = "";

	if (name.indexOf(':') > 0) {
	    prefix = name.substring(0, name.indexOf(':'));
	}

	return prefix;
    }

    /**
     * Returns the "localname" part of a QName, which is the whole
     * name if it has no prefix.
     *
     * @param element The QName of an element.
     * @return The local part of a QName.
     */
    public static String getLocalName(Element element) {
	String name = element.getTagName();

	if (name.indexOf(':') > 0) {
	    name = name.substring(name.indexOf(':')+1);
	}

	return name;
    }

    /**
     * Returns the namespace URI for the specified prefix at the
     * specified context node.
     *
     * @param node The context node.
     * @param prefix The prefix.
     * @return The namespace URI associated with the prefix, or
     * null if no namespace declaration exists for the prefix.
     */
    public static String getNamespaceURI(Node node, String prefix) {
	if (node == null || node.getNodeType() != Node.ELEMENT_NODE) {
	    return null;
	}

	if (prefix.equals("")) {
	    if (((Element) node).hasAttribute("xmlns")) {
		return ((Element) node).getAttribute("xmlns");
	    }
	} else {
	    String nsattr = "xmlns:" + prefix;
	    if (((Element) node).hasAttribute(nsattr)) {
		return ((Element) node).getAttribute(nsattr);
	    }
	}

	return getNamespaceURI(node.getParentNode(), prefix);
    }

    /**
     * Returns the namespace URI for the namespace to which the
     * element belongs.
     *
     * @param element The element.
     * @return The namespace URI associated with the namespace of the
     * element, or null if no namespace declaration exists for it.
     */
    public static String getNamespaceURI(Element element) {
	String prefix = getPrefix(element);
	return getNamespaceURI(element, prefix);
    }
}