"""|NumberingPart| and closely related objects."""

from ..opc.part import XmlPart
from ..shared import lazyproperty


class NumberingPart(XmlPart):
    """Proxy for the numbering.xml part containing numbering definitions for a document
    or glossary."""

    @classmethod
    def new(cls):
        """Return newly created empty numbering part, containing only the root
        ``<w:numbering>`` element."""
        raise NotImplementedError

    @lazyproperty
    def numbering_definitions(self):
        """The |_NumberingDefinitions| instance containing the numbering definitions
        (<w:num> element proxies) for this numbering part."""
        return _NumberingDefinitions(self._element)


class _NumberingDefinitions:
    """Collection of |_NumberingDefinition| instances corresponding to the ``<w:num>``
    elements in a numbering part."""

    def __init__(self, numbering_elm):
        super(_NumberingDefinitions, self).__init__()
        self._numbering = numbering_elm

    def __len__(self):
        return len(self._numbering.num_lst)