"""Registration facilities for DOM. This module should not be used

directly. Instead, the functions getDOMImplementation and

registerDOMImplementation should be imported from xml.dom."""

from xml.dom.minicompat import *  # isinstance, StringTypes

# This is a list of well-known implementations.  Well-known names

# should be published by posting to xml-sig@python.org, and are

# subsequently recorded in this file.

well_known_implementations = {

    'minidom':'xml.dom.minidom',

    '4DOM': 'xml.dom.DOMImplementation',

    }

# DOM implementations not officially registered should register

# themselves with their

registered = {}

def registerDOMImplementation(name, factory):

    """registerDOMImplementation(name, factory)

    Register the factory function with the name. The factory function

    should return an object which implements the DOMImplementation

    interface. The factory function can either return the same object,

    or a new one (e.g. if that implementation supports some

    customization)."""

    registered[name] = factory

def _good_enough(dom, features):

    "_good_enough(dom, features) -> Return 1 if the dom offers the features"

    for f,v in features:

        if not dom.hasFeature(f,v):

            return 0

    return 1

def getDOMImplementation(name = None, features = ()):

    """getDOMImplementation(name = None, features = ()) -> DOM implementation.

    Return a suitable DOM implementation. The name is either

    well-known, the module name of a DOM implementation, or None. If

    it is not None, imports the corresponding module and returns

    DOMImplementation object if the import succeeds.

    If name is not given, consider the available implementations to

    find one with the required feature set. If no implementation can

    be found, raise an ImportError. The features list must be a sequence

    of (feature, version) pairs which are passed to hasFeature."""

    import os

    creator = None

    mod = well_known_implementations.get(name)

    if mod:

        mod = __import__(mod, {}, {}, ['getDOMImplementation'])

        return mod.getDOMImplementation()

    elif name:

        return registered[name]()

    elif os.environ.has_key("PYTHON_DOM"):

        return getDOMImplementation(name = os.environ["PYTHON_DOM"])

    # User did not specify a name, try implementations in arbitrary

    # order, returning the one that has the required features

    if isinstance(features, StringTypes):

        features = _parse_feature_string(features)

    for creator in registered.values():

        dom = creator()

        if _good_enough(dom, features):

            return dom

    for creator in well_known_implementations.keys():

        try:

            dom = getDOMImplementation(name = creator)

        except StandardError: # typically ImportError, or AttributeError

            continue

        if _good_enough(dom, features):

            return dom

    raise ImportError,"no suitable DOM implementation found"

def _parse_feature_string(s):

    features = []

    parts = s.split()

    i = 0

    length = len(parts)

    while i < length:

        feature = parts[i]

        if feature[0] in "0123456789":

            raise ValueError, "bad feature name: %r" % (feature,)

        i = i + 1

        version = None

        if i < length:

            v = parts[i]

            if v[0] in "0123456789":

                i = i + 1

                version = v

        features.append((feature, version))

    return tuple(features)