#!/usr/bin/env python3
#    synacor.py - An implementation of the Synacor Challenge
#    Copyright © 2017  RunasSudo
#
#    This program is free software: you can redistribute it and/or modify
#    it under the terms of the GNU Affero General Public License as published by
#    the Free Software Foundation, either version 3 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 Affero General Public License for more details.
#
#    You should have received a copy of the GNU Affero General Public License
#    along with this program.  If not, see <http://www.gnu.org/licenses/>.

import re
import struct
import sys
import tarfile

IV_LEN = 3
CODE_LEN = 12

# Emulate 0731
def generate_code(R0, R1, R2, R3):
	R1data = SYN_MEM[R1+1:R1+1+SYN_MEM[R1]]
	R3data = SYN_MEM[R3+1:R3+1+SYN_MEM[R3]]
	
	assert len(R3data) == IV_LEN
	
	done = False
	while not done:
		code = ''
		for i in range(CODE_LEN):
			R5 = i % IV_LEN
			R6 = R3data[R5]
			R6 = (R6 * 0x1481) % 0x8000
			R6 = (R6 + 0x3039) % 0x8000
			R3data[R5] = R6
			R6 = R0 ^ R6
			R6 = R6 % len(R1data)
			if R6 + 1 <= R2:
				done = True
			R6 = R1data[R6]
			code += chr(R6)
	
	return code

def mirror_code(code):
	alphabet1 = 'dbqpwuiolxv8WTYUIOAHXVM'
	alphabet2 = 'bdpqwuiolxv8WTYUIOAHXVM'
	mirrored_code = ''
	for letter in reversed(code):
		if letter not in alphabet1:
			raise Exception('Cannot mirror unknown letter ' + letter)
		mirrored_code += alphabet2[alphabet1.index(letter)]
	return mirrored_code

# Read code into memory
SYN_MEM = [0] * 32768

with tarfile.open(sys.argv[1], 'r:gz') as challenge_file:
	with challenge_file.extractfile('challenge.bin') as data:
		i = 0
		while True:
			byteData = data.read(2)
			if len(byteData) < 2:
				break
			SYN_MEM[i] = struct.unpack('<H', byteData)[0]
			i += 1
	
	# Extract first code
	with challenge_file.extractfile('arch-spec') as data:
		spec_data = data.read().decode('utf-8')
		print(re.search(r"Here's a code for the challenge website: (............)", spec_data).group(1))

# Emulate 06bb
for R1 in range(0x17b4, 0x7562):
	R0 = SYN_MEM[R1]
	R0 ^= pow(R1, 2, 32768)
	R0 ^= 0x4154
	SYN_MEM[R1] = R0

# Basic codes
print(bytes(SYN_MEM[0x00f5:0x010c:2]).decode('utf-8'))

R0 = 0x68e3
R2 = (SYN_MEM[0x0426] + SYN_MEM[0x0427]) % 0x8000
strlen = SYN_MEM[R0]
strbuf = ''
for i in range(strlen):
	encrypted = SYN_MEM[R0 + 1 + i]
	decrypted = encrypted ^ R2
	strbuf += chr(decrypted)
print(re.match(r"The self-test completion code is: (............)", strbuf).group(1))

# Generated codes
# Calls to 0731
CODE_PARAMS = [
	(0x0058, 0x650a, 0x7fff, 0x6e8b), # R0 from the maze
	(0x1092, 0x650a, 0x7fff, 0x6eed),
	(0x6486, 0x650a, 0x7fff, 0x7239), # R0 is R7 from Ackermann
	(0x0b3b, 0x650a, 0x7fff, 0x73df), # R0 from the dots on the coins
	(0x7714, 0x653f, 0x0004, 0x74f6), # R0 based on solution to vaults
]

for cp in CODE_PARAMS:
	print(generate_code(*cp) if cp[1] != 0x653f else mirror_code(generate_code(*cp)))