"""

 The GeometryProxy object, allows for lazy-geometries.  The proxy uses

 Python descriptors for instantiating and setting Geometry objects

 corresponding to geographic model fields.

 Thanks to Robert Coup for providing this functionality (see #4322).

"""

from types import NoneType, StringType, UnicodeType

class GeometryProxy(object): 

    def __init__(self, klass, field): 

        """

        Proxy initializes on the given Geometry class (not an instance) and 

        the GeometryField.

        """

        self._field = field 

        self._klass = klass

    def __get__(self, obj, type=None): 

        """

        This accessor retrieves the geometry, initializing it using the geometry

        class specified during initialization and the HEXEWKB value of the field.  

        Currently, only GEOS or OGR geometries are supported.

        """

        # Getting the value of the field.

        geom_value = obj.__dict__[self._field.attname] 

        if isinstance(geom_value, self._klass): 

            geom = geom_value

        elif (geom_value is None) or (geom_value==''):

            geom = None

        else: 

            # Otherwise, a Geometry object is built using the field's contents,

            # and the model's corresponding attribute is set.

            geom = self._klass(geom_value)

            setattr(obj, self._field.attname, geom) 

        return geom 

    def __set__(self, obj, value):

        """

        This accessor sets the proxied geometry with the geometry class

        specified during initialization.  Values of None, HEXEWKB, or WKT may

        be used to set the geometry as well.

        """

        # The OGC Geometry type of the field.

        gtype = self._field._geom

        # The geometry type must match that of the field -- unless the

        # general GeometryField is used.

        if isinstance(value, self._klass) and (str(value.geom_type).upper() == gtype or gtype == 'GEOMETRY'):

            # Assigning the SRID to the geometry.

            if value.srid is None: value.srid = self._field._srid

        elif isinstance(value, (NoneType, StringType, UnicodeType)):

            # Set with None, WKT, or HEX

            pass

        else:

            raise TypeError('cannot set %s GeometryProxy with value of type: %s' % (obj.__class__.__name__, type(value)))

        # Setting the objects dictionary with the value, and returning.

        obj.__dict__[self._field.attname] = value 

        return value