import argparse
import os, os.path
import zipfile
import io
		
def readui32(file):
	bytes = file.read(4)
	number = bytes[0]
	number += bytes[1] << 8
	number += bytes[2] << 16
	number += bytes[3] << 24
	return number
			
def skip2zip(file):
	SIGNATURE = b'PK\x05\x06'

	# retrieve the file size
	file.seek(0, 2)
	filesize = file.tell()
	
	# scan the last 65k (2^16) for the zip signature
	signature_position = filesize
	while signature_position > filesize - (2 << 16):
		file.seek(signature_position, 0)
		data = file.read(len(SIGNATURE))
		if data == SIGNATURE:
			break
		signature_position -= 1
	else:
		raise ValueError("Corrupted zip archive.")
		
	# skip 8 bytes
	file.seek(8, 1) 
	
	# read size and offset of central directory
	size = readui32(file)
	offset = readui32(file)
	
	# Calculate beginning of the zip file:
	# There is a "central directory" with the size 'size' located at 'offset' (relative to the zip 
	# file). The signature is appended directly after the central directory. We have already found 
	# the signature start and know the size of the central directory, so we can calculate the 
	# beginning of the central directory via 'signature_position - size'. The result is the "real"
	# offset inside the packed executable. The supposed offset inside the zip file is stored at 
	# 'offset', so we can calculate the beginning of the zip-file.
	start = (signature_position - size) - offset
	
	# seek to the beginning position
	file.seek(start, 0)
	

def unpack(executablename, unzipdestination=None, lovefilename=True):
	with open(executablename, 'rb') as executable:
		skip2zip(executable)
		
		data = executable.read()
	
	if lovefilename:
		with open(lovefilename, 'wb') as lovefile:
			lovefile.write(data)
		
	if unzipdestination:
		if not os.path.isdir(unzipdestination):
			os.makedirs(unzipdestination)
			
		zipdata = io.BytesIO(data)
		with zipfile.ZipFile(zipdata, 'r') as zip:
			zip.extractall(unzipdestination)
				
	
if __name__=="__main__":
	parser = argparse.ArgumentParser(description='Unpack a love executable.')
	parser.add_argument('-x', '--extract', metavar="DESTINATION", type=str, help="Unzip files to this folder")
	parser.add_argument('-l', '--love', metavar="DESTINATION", type=str, help="Filename of the .love file to write.")
	parser.add_argument('executable', type=str, help='Executable to unpack')
	
	args = parser.parse_args()
	
	unpack(args.executable, unzipdestination=args.extract, lovefilename=args.love)