"""NDG XACML ElementTree based reader for AttributeValue type

NERC DataGrid
"""
__author__ = "P J Kershaw"
__date__ = "16/03/10"
__copyright__ = "(C) 2010 Science and Technology Facilities Council"
__contact__ = "Philip.Kershaw@stfc.ac.uk"
__license__ = "BSD - see LICENSE file in top-level directory"
__contact__ = "Philip.Kershaw@stfc.ac.uk"
__revision__ = "$Id$"
from ndg.xacml.core.attributevalue import (AttributeValue, 
                                           AttributeValueClassFactory)
from ndg.xacml.parsers import XMLParseError
from ndg.xacml.parsers.etree import QName
from ndg.xacml.parsers.etree.expressionreader import ExpressionReader


class AttributeValueReader(ExpressionReader):
    '''ElementTree based XACML Expression type parser
    '''
    TYPE = AttributeValue
    FACTORY = AttributeValueClassFactory()
    
    def __call__(self, obj):
        """Parse *AttributeValue type element - override this method instead of
        _parseExtension since AttributeValue class is virtual.  A sub-type can
        be instantiated only once the data type attribute is parsed
        """
        elem = super(AttributeValueReader, self)._parse(obj)
        
        xacmlType = self.__class__.TYPE
        localName = QName.getLocalPart(elem.tag)
        if localName != xacmlType.ELEMENT_LOCAL_NAME:
            raise XMLParseError("No \"%s\" element found" % 
                                xacmlType.ELEMENT_LOCAL_NAME)
            
        # Unpack *required* attributes from top-level element
        elemAttributeValues = []
        for attributeName in (xacmlType.DATA_TYPE_ATTRIB_NAME,):
            attributeValue = elem.attrib.get(attributeName)
            if attributeValue is None:
                raise XMLParseError('No "%s" attribute found in "%s" element' %
                                    (attributeName, 
                                     xacmlType.ELEMENT_LOCAL_NAME))
                
            elemAttributeValues.append(attributeValue)
             
        attributeValueClass = self.__class__.FACTORY(elemAttributeValues[0])
        attributeValue = attributeValueClass()
        attributeValue.dataType = elemAttributeValues[0]
        self._parseExtension(elem, attributeValue)
        
        return attributeValue
    
    def _parseExtension(self, elem, attributeValue):
        if elem.text is None:
            raise XMLParseError('No attribute value element found parsing %r' % 
                                AttributeValueReader.TYPE.ELEMENT_LOCAL_NAME) 
            
        attributeValue.value = elem.text