#!/usr/bin/env python3

"""
Toggle the bit at the specified offset.
Syntax: <cmdname> chall byte-offset bit-offset
https://unix.stackexchange.com/questions/196251/change-only-one-bit-in-a-file
"""

from tempfile import NamedTemporaryFile
from os import chmod
from subprocess import CalledProcessError, TimeoutExpired, check_call
from shutil import copyfile



yourFile = NamedTemporaryFile(delete=True)
copyfile("/home/chall/chall",yourFile.name)
chmod(yourFile.name,0o777)

print("Welcome to the super Flipper.")
print("====================================================")
try:
	bytepos = int(input("Please enter the byte-offset you want to flip (0x80-0x139): "),16)
	bitpos = int(input("Please enter the bitposition you want to flip at byte-offset(7-0): "),16)
except ValueError:
	print("numbers only please...;)")
	exit(-1)

if(bytepos < 0x80 or bytepos > 0x139 or bitpos < 0 or bitpos > 7 ):
	print("behave kid, behave...ò.ó")
	exit(-1)

patch = open(yourFile.name,"r+b")

patch.seek(bytepos, 0)
c = patch.read(1)
toggled = bytes( [ ord(c)^(1<<bitpos) ] ) 

patch.seek(-1, 1) 
patch.write(toggled)
patch.close()

yourFile.file.close()
try:
	print("\n============ Running Challenge now! ================")
	check_call([yourFile.name],timeout=10)
except CalledProcessError:
	print("\n============ you bricked it:> ============")
except TimeoutExpired:
	print("\n============= got the flag?:> =============")