#!/usr/bin/env python

#
#    Copyright (c) 2013-2017 Nest Labs, Inc.
#    All rights reserved.
#
#    Licensed under the Apache License, Version 2.0 (the "License");
#    you may not use this file except in compliance with the License.
#    You may obtain a copy of the License at
#
#        http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS,
#    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#    See the License for the specific language governing permissions and
#    limitations under the License.
#

#
#    @file
#      This file implements a Python script for generating and
#      verifying check digits using Verhoeff's algorithm. In addition,
#      the script may be used to generate Verhoeff multiply tables for
#      a given base.
#

import sys

__all__ = [ 'ComputeCheckChar',   'VerifyCheckChar',
			'ComputeCheckChar16', 'VerifyCheckChar16',
			'ComputeCheckChar32', 'VerifyCheckChar32',
			'ComputeCheckChar36', 'VerifyCheckChar36' ]

CharSet_Base10 = "0123456789"
CharSet_Base16 = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"
CharSet_Base32 = "0123456789ABCDEFGHJKLMNPRSTUVWXY" # Excludes I, O, Q and Z
CharSet_Base36 = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"

PermTable_Base10 = [ 1,   5,  7,  6,  2,  8,  3,  0,  9,  4 ]
PermTable_Base16 = [ 4,   7,  5, 14,  8, 12, 15,  0,  2, 11,  3, 13, 10,  6,  9,  1 ]
PermTable_Base32 = [ 7,   2,  1, 30, 16, 20, 27, 11, 31,  6,  8, 13, 29,  5, 10, 21, 22,  3, 24,  0, 23, 25, 12,  9, 28, 14,  4, 15, 17, 18, 19, 26 ]
PermTable_Base36 = [ 29,  0, 32, 11, 35, 20,  7, 27,  2,  4, 19, 28, 30,  1,  5, 12,  3,  9, 16, 22,  6, 33,  8, 24, 26, 21, 14, 10, 34, 31, 15, 25, 17, 13, 23, 18 ]

def DihedralMultiply(x, y, n):
	n2 = n * 2

	x = x % n2
	y = y % n2

	if (x < n):
		if (y < n):
			return (x + y) % n
		else:
			return ((x + (y - n)) % n) + n
	else:
		if (y < n):
			return ((n + (x - n) - y) % n) + n
		else:
			return (n + (x - n) - (y - n)) % n

def DihedralInvert(val, n):
	if (val > 0 and val < n):
		return n - val
	else:
		return val

def Permute(val, permTable, iterCount):
	val = val % len(permTable);
	if (iterCount == 0):
		return val
	else:
		return Permute(permTable[val], permTable, iterCount - 1)

def _ComputeCheckChar(str, strLen, polygonSize, permTable, charSet):
	str = str.upper()
	c = 0
	for i in range(1, strLen+1):
		ch = str[strLen - i]
		val = charSet.index(ch)
		p = Permute(val, permTable, i)
		c = DihedralMultiply(c, p, polygonSize)
	c = DihedralInvert(c, polygonSize)
	return charSet[c]

def ComputeCheckChar(str, charSet=CharSet_Base10):
	return _ComputeCheckChar(str, len(str), polygonSize=5, permTable=PermTable_Base10, charSet=charSet)

def VerifyCheckChar(str, charSet=CharSet_Base10):
	expectedCheckCh = _ComputeCheckChar(str, len(str)-1, polygonSize=5, permTable=PermTable_Base10, charSet=CharSet_Base10)
	return str[-1] == expectedCheckCh  

def ComputeCheckChar16(str, charSet=CharSet_Base16):
	return _ComputeCheckChar(str, len(str), polygonSize=8, permTable=PermTable_Base16, charSet=charSet)

def VerifyCheckChar16(str, charSet=CharSet_Base16):
	expectedCheckCh = _ComputeCheckChar(str, len(str)-1, polygonSize=8, permTable=PermTable_Base16, charSet=charSet)
	return str[-1] == expectedCheckCh  

def ComputeCheckChar32(str, charSet=CharSet_Base32):
	return _ComputeCheckChar(str, len(str), polygonSize=16, permTable=PermTable_Base32, charSet=charSet)

def VerifyCheckChar32(str, charSet=CharSet_Base32):
	expectedCheckCh = _ComputeCheckChar(str, len(str)-1, polygonSize=16, permTable=PermTable_Base32, charSet=charSet)
	return str[-1] == expectedCheckCh  

def ComputeCheckChar36(str, charSet=CharSet_Base36):
	return _ComputeCheckChar(str, len(str), polygonSize=18, permTable=PermTable_Base36, charSet=charSet)

def VerifyCheckChar36(str, charSet=CharSet_Base36):
	expectedCheckCh = _ComputeCheckChar(str, len(str)-1, polygonSize=18, permTable=PermTable_Base36, charSet=charSet)
	return str[-1] == expectedCheckCh  


if __name__ == "__main__":

	usage = """Usage: %s <command> [ <args> ]

Commands:
  generate <string>
  verify <string-with-check-digit>
  gen-multiply-table <base>
""" % (sys.argv[0])

	if (len(sys.argv) < 2):
		print usage
	elif (sys.argv[1] == "generate"):
		if (len(sys.argv) < 3):
			print usage
			sys.exit(-1)
		ch = ComputeCheckChar(sys.argv[2])
		print "%s%c" % (sys.argv[2], ch)
	elif (sys.argv[1] == "verify"):
		if (len(sys.argv) < 3):
			print usage
			sys.exit(-1)
		if (VerifyCheckChar(sys.argv[2])):
			print "%s is VALID" % (sys.argv[2])
			sys.exit(0)
		else:
			print "%s is INVALID" % (sys.argv[2])
			sys.exit(-1)
	elif (sys.argv[1] == "gen-multiply-table"):
		if (len(sys.argv) < 3):
			print usage
			sys.exit(-1)
		base = int(sys.argv[2])
		if (base % 2 != 0):
			print "Base must be even"
			sys.exit(-1);
		n = base / 2
		for x in range(0, base):
			sys.stdout.write("    ")
			for y in range(0, base):
				o = DihedralMultiply(x, y, n)
				sys.stdout.write("%2d, " % o)
			sys.stdout.write("\n")
	else:
		print usage
		sys.exit(-1)
	sys.exit(0)