######################################################################

#  This file should be kept compatible with Python 2.3, see PEP 291. #

######################################################################

import sys

from ctypes import *

_array_type = type(c_int * 3)

def _other_endian(typ):

    """Return the type with the 'other' byte order.  Simple types like

    c_int and so on already have __ctype_be__ and __ctype_le__

    attributes which contain the types, for more complicated types

    only arrays are supported.

    """

    try:

        return getattr(typ, _OTHER_ENDIAN)

    except AttributeError:

        if type(typ) == _array_type:

            return _other_endian(typ._type_) * typ._length_

        raise TypeError("This type does not support other endian: %s" % typ)

class _swapped_meta(type(Structure)):

    def __setattr__(self, attrname, value):

        if attrname == "_fields_":

            fields = []

            for desc in value:

                name = desc[0]

                typ = desc[1]

                rest = desc[2:]

                fields.append((name, _other_endian(typ)) + rest)

            value = fields

        super(_swapped_meta, self).__setattr__(attrname, value)

################################################################

# Note: The Structure metaclass checks for the *presence* (not the

# value!) of a _swapped_bytes_ attribute to determine the bit order in

# structures containing bit fields.

if sys.byteorder == "little":

    _OTHER_ENDIAN = "__ctype_be__"

    LittleEndianStructure = Structure

    class BigEndianStructure(Structure):

        """Structure with big endian byte order"""

        __metaclass__ = _swapped_meta

        _swappedbytes_ = None

elif sys.byteorder == "big":

    _OTHER_ENDIAN = "__ctype_le__"

    BigEndianStructure = Structure

    class LittleEndianStructure(Structure):

        """Structure with little endian byte order"""

        __metaclass__ = _swapped_meta

        _swappedbytes_ = None

else:

    raise RuntimeError("Invalid byteorder")