from ctypes import c_void_p

from types import NoneType

from django.contrib.gis.gdal.error import GDALException

class GDALBase(object):

    """

    Base object for GDAL objects that has a pointer access property

    that controls access to the underlying C pointer.

    """

    # Initially the pointer is NULL.

    _ptr = None

    # Default allowed pointer type.

    ptr_type = c_void_p

    # Pointer access property.

    def _get_ptr(self):

        # Raise an exception if the pointer isn't valid don't

        # want to be passing NULL pointers to routines --

        # that's very bad.

        if self._ptr: return self._ptr

        else: raise GDALException('GDAL %s pointer no longer valid.' % self.__class__.__name__)

    def _set_ptr(self, ptr):

        # Only allow the pointer to be set with pointers of the

        # compatible type or None (NULL).

            self._ptr = self.ptr_type(ptr)

        elif isinstance(ptr, (self.ptr_type, NoneType)):

            self._ptr = ptr

        else:

            raise TypeError('Incompatible pointer type')

    ptr = property(_get_ptr, _set_ptr)