""" View validation code (using assertions, not the RNG schema). """

import collections
import logging

_logger = logging.getLogger(__name__)


_validators = collections.defaultdict(list)
def valid_view(arch):
    for pred in _validators[arch.tag]:
        if not pred(arch):
            _logger.error("Invalid XML: %s", pred.__doc__)
            return False
    return True


def validate(*view_types):
    """ Registers a view-validation function for the specific view types
    """
    def decorator(fn):
        for arch in view_types:
            _validators[arch].append(fn)
        return fn
    return decorator


@validate('form')
def valid_page_in_book(arch):
    """A `page` node must be below a `notebook` node."""
    return not arch.xpath('//page[not(ancestor::notebook)]')


@validate('graph')
def valid_field_in_graph(arch):
    """ Children of ``graph`` can only be ``field`` """
    return all(
        child.tag == 'field'
        for child in arch.xpath('/graph/*')
    )


@validate('tree')
def valid_field_in_tree(arch):
    """ Children of ``tree`` view must be ``field`` or ``button``."""
    return all(
        child.tag in ('field', 'button')
        for child in arch.xpath('/tree/*')
    )


@validate('form', 'graph', 'tree')
def valid_att_in_field(arch):
    """ ``field`` nodes must all have a ``@name`` """
    return not arch.xpath('//field[not(@name)]')


@validate('form')
def valid_att_in_label(arch):
    """ ``label`` nodes must have a ``@for`` or a ``@string`` """
    return not arch.xpath('//label[not(@for or @string)]')


@validate('form')
def valid_att_in_form(arch):
    return True


@validate('form')
def valid_type_in_colspan(arch):
    """A `colspan` attribute must be an `integer` type."""
    return all(
        attrib.isdigit()
        for attrib in arch.xpath('//@colspan')
    )


@validate('form')
def valid_type_in_col(arch):
    """A `col` attribute must be an `integer` type."""
    return all(
        attrib.isdigit()
        for attrib in arch.xpath('//@col')
    )