# XML DOM tree manipulation

from xml.dom import Node

class MappingException(Exception): pass

def by_tag_name(parent, name):

    node = parent.lastChild

    while node != None and\

    not (node.nodeType == Node.ELEMENT_NODE and node.tagName == name):

        node = node.previousSibling

    return node

def value(node):

    if node.firstChild != None: return node.firstChild.nodeValue

    else: return node.nodeValue

def by_path(doc, path, create=False, parent=None):

    if not parent: parent = doc.documentElement

    for elem in path:

        node = None

        if elem.is_attr: node = parent.getAttributeNode(elem.name)

        elif elem.name == '.': node = parent

        else: node = by_tag_name(parent, elem.name)

        if node != None and elem.value != None and value(node) != elem.value:

            node = None

        for attr in elem.attrs:

            if by_path(doc, attr, parent=node) == None: node = None; break

        if node == None:

            if not create: return None

            if elem.is_attr:

                parent.setAttribute(elem.name, '')

                node = parent.getAttributeNode(elem.name)

            else: node = parent.appendChild(doc.createElement(elem.name))

            if elem.value != None:

                if node.nodeType == Node.ELEMENT_NODE:

                    node.appendChild(doc.createTextNode(elem.value))

                else: node.nodeValue = elem.value

            for attr in elem.attrs: by_path(doc, attr, create, node)

        parent = node

    return parent