Fix Splatoon 2 save file CRC in the header (for plaintext body)

crcfix.py

import zlib
import struct
import os
import sys

DEFAULT_FILENAME = "save.dat"

def fixcrc(fileName):
    HEADER_SIZE = 0x10
    FOOTER_SIZE = 0x30
    BODY_SIZES = [0x483A0, 0x86800, 0x88D50]
    HASH_OFFSET = 0x8
    
    if not os.path.isfile(fileName):
        print "Cannot access file", fileName
        return
    
    file_body_size = os.path.getsize(fileName)
    
    if file_body_size-HEADER_SIZE not in BODY_SIZES:
        file_body_size = file_body_size - FOOTER_SIZE
    if file_body_size-HEADER_SIZE not in BODY_SIZES:
        print "The save data size (", hex(file_body_size), ") is incorrect."
        return
    
    with open(fileName, mode='r+') as file:
        file.seek(HEADER_SIZE, 0)
        hashValue = zlib.crc32(file.read(file_body_size)) & 0xffffffff
        hashValueLE = struct.pack('<I', hashValue)
        
        file.seek(HASH_OFFSET, 0)
        file.write(hashValueLE)
        
        print "CRC has been set to", hashValueLE.encode('hex')

if len(sys.argv) > 1:
    fixcrc(sys.argv[1])
else:
    fixcrc(DEFAULT_FILENAME)