# General XML utilities

from xml.dom import minidom
from xml import xpath
import codecs

def getFileWriter(fileHandle):
    """Gets a 'writer' for a file object that encodes
    as UTF-8"""
    return codecs.lookup("UTF-8").streamwriter(fileHandle)

def writexml(doc, fileHandle):
    """Writes an XML document to a file handle"""
    doc.writexml(getFileWriter(fileHandle), encoding="UTF-8")

def getNodesFromXPath(document, path):
    """Selects nodes specified by 'path' from 'document',
    where path is a string or a compiled xpath object"""
    if isinstance(path, basestring):
        path = xpath.Compile(path)
    return path.select(xpath.CreateContext(document))

_rootxpath = xpath.Compile('/')
def getRoot(doc):
    """Returns the root node of a document"""
    return getNodesFromXPath(doc, _rootxpath)[0]


# Classes to help us with modifications
class RemoveNode:
    def act(self, node):
        if isinstance(node, minidom.Attr):
            node.ownerElement.removeAttribute(node.name)
        else:
            node.parentNode.removeChild(node)

class GeneralReplaceContents:
    """Replace the contents of a node,
    with user providable function for calculating replacement text
    """
    def __init__(self, replacefunc):
        self.replacefunc = replacefunc
    def act(self, node):
        origText = u''.join(c.toxml() for c in node.childNodes)

        # Usually replacefunc will just return text,
        # but we allow it to return xml as well
        newNodes = minidom.parseString(u'<dummy>' + self.replacefunc(origText) + u'</dummy>' )
        # newNodes is a DOM instance, and it is has a dummy
        # element wrapping the nodes we actually want.
        node.childNodes = newNodes.childNodes[0].childNodes

class ReplaceContents(GeneralReplaceContents):
    def __init__(self, replacementtext):
        assert isinstance(replacementtext, unicode)
        def _replacefunc(text):
            return replacementtext
        self.replacefunc = _replacefunc

def do_replacements(doc, replacements):
    ctx = xpath.CreateContext(doc)
    for path, action in replacements.items():
        xp = xpath.Compile(path)
        for n in xp.select(ctx):
            action.act(n)