'''
There are various snippets of code in here for doing various hash
and crc checking.  I wrote none of them, mostly because I was
relatively unconcerned with the detail of CRC16 and CRC31. Proper
credits have been preserved.

Per's SFV is a simple Simple File Verificator that you can use to
verify that a file has not changed.
Copyright (C) 2006  Per Myren <per.myren@gmail.com>
Distributed under the GPL v2

modified by jason moiron to remove wx cruft and to allow file objects 
as arguments to CheckSum()

usage:
    CheckSum(file_or_filename).getfilecrc()
'''
import zlib, md5, struct, binascii, os

class CRC32:
    def __init__(self, s=''):
        self.value = zlib.crc32(s)

    def update(self, s):
        self.value = zlib.crc32(s, self.value)

    def digest(self):
        return struct.pack('>I',self.value)

class _CRC16:
    def __init__(self, s=''):
        self.value = crc16(s)

    def update(self, s):
        self.value = crc16(s, self.value)

    def digest(self):
        return struct.pack('>I',self.value)

class CheckSum:
    def __init__(self, filename):
        self.filename = filename

    def _getCheckSum(self, filename, checksumtype):
        try:
            if isinstance(filename, file):
                f = filename
            elif isinstance(filename, str):
                f = file(filename, 'rb')
            while True:
                x = f.read(65536)
                if not x:
                    #f.close()
                    return checksumtype.digest()
                checksumtype.update(x)

        except (IOError, OSError):
            return "No such file"

    def getfilemd5(self):
        return binascii.hexlify(self._getCheckSum(self.filename, md5.new()))

    def getfilecrc(self):
        return binascii.hexlify(self._getCheckSum(self.filename, CRC32()))

"""
Modified from:
http://news.hping.org/comp.lang.python.archive/18112.html

Original License:
crc16 by Bryan G. Olson, 2005
This module is free software and may be used and
distributed under the same terms as Python itself.
"""

from array import array

def crc16(string, value=0xffff):
    "Modified the default of 'value' so no inversion is necessary"
    for ch in string:
        value = crc16table[ord(ch) ^ (value & 0xff)] ^ (value >> 8)
    return value

# CRC-16 poly: p(x) = x**16 + x**15 + x**2 + 1
# top bit implicit, reflected
poly = 0xa001
crc16table = array('H')
for byte in range(256):
    crc = 0
    for bit in range(8):
        if (byte ^ crc) & 1:
            crc = (crc >> 1) ^ poly
        else:
            crc >>= 1
        byte >>= 1
    crc16table.append(crc)