#  c1218/utilities.py
#
#  Copyright 2011 Spencer J. McIntyre <SMcIntyre [at] SecureState [dot] net>
#
#  This program is free software; you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation; either version 2 of the License, or
#  (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program; if not, write to the Free Software
#  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
#  MA 02110-1301, USA.

from __future__ import unicode_literals

import struct

import crcelk

def check_data_checksum(data, checksum):
	if isinstance(checksum, int):
		checksum = struct.pack('B', checksum)
	return data_checksum(data) == checksum

def data_checksum(data):
	chksum = 0
	for i in struct.unpack('B' * len(data), data):
		chksum += i
	chksum = ((chksum - 1) & 0xff) ^ 0xff
	return struct.pack('B', chksum)

def packet_checksum(data):
	chksum = crcelk.CRC_HDLC.calc_bytes(data)
	return struct.pack('<H', chksum)
