# XPath-based XML tree manipulation

import copy

import xml_dom

import xpath

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

    # Warning: The last_only optimization may put data that should be together

    # into separate nodes

    if parent == None: parent = doc.documentElement

    if last_only == None: last_only = create

    elem_idx = 0

    for elem in path:

        # Find possible matches

        children = []

        if elem.is_attr:

            child = parent.getAttributeNode(elem.name)

            if child != None: children = [child]

        elif elem.name == '.': children = [parent]

        else:

            children = xml_dom.by_tag_name(parent, elem.name,

            last_only and (elem.attrs == [] or xpath.is_instance(elem)))

        # Check each match

        node = None

        for child in children:

            is_match = elem.value == None or xml_dom.value(child) == elem.value

            for attr in elem.attrs:

                if not is_match: break

                is_match = get(doc, attr, False, last_only, child) != None

            if is_match: node = child; break

        # Create node

        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: xml_dom.set_value(doc, node, elem.value)

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

        # Follow pointer

        if elem.is_ptr:

            path = copy.deepcopy(path[elem_idx+1:]) # rest of path

            id_elem = xpath.backward_id(path[xpath.instance_level])

            if id_elem != None:

                # backward (child-to-parent) pointer with target ID attr

                xpath.set_value(id_elem, xml_dom.get_id(node))

            else: # forward (parent-to-child) pointer

                id_ = xml_dom.value(node)

                obj_path = xpath.obj(path) # target object

                if id_ == None or get(doc, obj_path, False, True) == None:

                    # no target or target attrs don't match

                    if not create: return None

                    # Use last target object's ID + 1

                    obj_path[-1].attrs = [] # just get by tag name

                    last = get(doc, obj_path, False, True)

                    if last != None: id_ = str(int(xml_dom.get_id(last)) + 1)

                    else: id_ = '0'

                    # Will append if target attrs didn't match. Place ! in XPath

                    # after element to fork at to avoid this.

                    xml_dom.set_value(doc, node, id_)

                else: last_only = False

                xpath.set_id(path, id_)

            return get(doc, path, create, last_only)

        parent = node

        elem_idx += 1

    return parent