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+#!/usr/bin/env python3
+# Startdate: 2024-03-08-6 15:28
+# File: srb_lib.py
+# Purpose: library for srb.exe savegame hacking
+# SPDX-License-Identifier: GPL-3.0-only
+# History:
+# Usage:
+#    from srb.py
+# Reference:
+#    blog posts 2024-03
+#    <https://github.com/8051Enthusiast/delsum>
+#    crc width=32 poly=0x4c11db7 init=0x0 xorout=0x235b4b9c refin=false refout=false out_endian=little
+#    Incorrect functions: https://gist.github.com/djsweet/3477115595efab31905be7000bb013bc FAILED
+#    Fuctions that worked: https://gist.github.com/Lauszus/6c787a3bc26fea6e842dfb8296ebd630 Author: Lauszus
+#    https://stackoverflow.com/questions/46109815/reversing-the-byte-order-of-a-string-containing-hexadecimal-characters
+#    https://gamefaqs.gamespot.com/pc/930591-snoopy-vs-the-red-baron/faqs/46161
+# Documentation:
+#    winetricks vd=1024x768
+#    winetricks vd=off
+# Dependencies:
+#    python3-crcmod
+
+import sys, struct
+srb_lib_version = "20240309a"
+
+# Table of byte positions of values in the savegame file, minus the first four bytes which are the checksum. Due to zero-indexing of python lists, but for ease of usage, we will always put a zero as the value of index 0. That is, profile 1 will use index 1 of the list.
+# money is 0x270 bytes after the "Z<dddddddd" start.
+PROFILE_START_POSITION = [0, 0x10, 0x142C, 0x2848]
+POS_MONEY = 0x270
+POS_EQUIPPED_WEAPON = 0x284
+
+WEAPONS = [
+   "undefined", # 0x0
+   "undefined", # secondary weapon is a single machine gun?!
+   "undefined",
+   "undefined",
+   "undefined",
+   "Potato Gun", # 0x5
+   "Stinger",
+   "Woodstock Missile",
+   "Water Balloon Cannon",
+   "Snow Blower",
+   "Fire Boomerang", # 0xA
+   "Lightning Rod",
+   "Bottle Rockets",
+   "Roman Candles",
+   "10 Gauge Pumpkin",
+   "undefined", # 0xF
+]
+
+# DEFINE FUNCTIONS
+def ferror(*args, **kwargs):
+   print(*args, file=sys.stderr, **kwargs)
+
+def debuglev(_numbertocheck, debuglevel):
+   # if _numbertocheck <= debuglevel then return truthy
+   _debuglev = False
+   try:
+      if int(_numbertocheck) <= int(debuglevel):
+         _debuglev = True
+   except Exception as e:
+      pass
+   return _debuglev
+
+def read_file(filename):
+   """ Return the stored checksum and contents of the file """
+   with open(filename, 'rb') as f:
+      # Read the entire file
+      file_contents = f.read()
+      checksum = file_contents[0:4]
+      file_contents_without_checksum = file_contents[4:]
+   return checksum, file_contents_without_checksum
+
+def write_file(filename, checksum, data):
+   """ Write the checksum and data to the file. We are assuming the checksum is already correct. """
+   print(f"debug: checksum(type={type(checksum).__name__})={checksum}")
+   if type(checksum) == int:
+      checksum = checksum
+   elif type(checksum) == str:
+      checksum = int(checksum)
+   elif type(checksum) == bytes:
+      checksum = int.from_bytes(checksum)
+   with open(filename, 'wb') as f:
+      f.write(struct.pack('>L',checksum))
+      #f.write(struct.pack('>I',int(checksum)))
+      f.write(data)
+
+######## start copy-paste 2
+#  https://gist.github.com/Lauszus/6c787a3bc26fea6e842dfb8296ebd630
+
+def reflect_data(x, width):
+   # See: https://stackoverflow.com/a/20918545
+   if width == 8:
+      x = ((x & 0x55) << 1) | ((x & 0xAA) >> 1)
+      x = ((x & 0x33) << 2) | ((x & 0xCC) >> 2)
+      x = ((x & 0x0F) << 4) | ((x & 0xF0) >> 4)
+   elif width == 16:
+      x = ((x & 0x5555) << 1) | ((x & 0xAAAA) >> 1)
+      x = ((x & 0x3333) << 2) | ((x & 0xCCCC) >> 2)
+      x = ((x & 0x0F0F) << 4) | ((x & 0xF0F0) >> 4)
+      x = ((x & 0x00FF) << 8) | ((x & 0xFF00) >> 8)
+   elif width == 32:
+      x = ((x & 0x55555555) << 1) | ((x & 0xAAAAAAAA) >> 1)
+      x = ((x & 0x33333333) << 2) | ((x & 0xCCCCCCCC) >> 2)
+      x = ((x & 0x0F0F0F0F) << 4) | ((x & 0xF0F0F0F0) >> 4)
+      x = ((x & 0x00FF00FF) << 8) | ((x & 0xFF00FF00) >> 8)
+      x = ((x & 0x0000FFFF) << 16) | ((x & 0xFFFF0000) >> 16)
+   else:
+      raise ValueError('Unsupported width')
+   return x
+
+def crc_poly(data, n, poly, crc=0, ref_in=False, ref_out=False, xor_out=0):
+   g = 1 << n | poly  # Generator polynomial
+   # Loop over the data
+   for d in data:
+      # Reverse the input byte if the flag is true
+      if ref_in:
+         d = reflect_data(d, 8)
+      # XOR the top byte in the CRC with the input byte
+      crc ^= d << (n - 8)
+      # Loop over all the bits in the byte
+      for _ in range(8):
+         # Start by shifting the CRC, so we can check for the top bit
+         crc <<= 1
+         # XOR the CRC if the top bit is 1
+         if crc & (1 << n):
+            crc ^= g
+   # Reverse the output if the flag is true
+   if ref_out:
+      crc = reflect_data(crc, n)
+   # Return the CRC value
+   return crc ^ xor_out
+##### end copy-paste 2
+
+def _get_data_from_data_object(data_object):
+   """ Helper function to either open file, or pass bytes through. """
+   if type(data_object) == str:
+      _, data = read_file(data_object)
+   elif type(data_object) == bytes:
+      data = data_object
+   return data
+
+def _convert_dec_to_reverse_bytes(num_dec):
+   """ Helper function to turn a given decimal value into the little-endian values for insertion into the data. """
+   # Here is how to do this manually.
+   #num_str = str(hex(num_dec))[2:]
+   #num_str = ("0" if len(num_str) % 2 else "") + num_str
+   #num_bytes = bytearray.fromhex(num_str)
+   #num_bytes.reverse()
+   #return bytes(num_bytes)
+   # I learned how to do this the pythonic way.
+   return struct.pack('<i',num_dec)
+
+def get_money(data_object,profile_id):
+   """ Print in decimal the current money value of the profile_id. """
+   data = _get_data_from_data_object(data_object)
+   money_dec = data[PROFILE_START_POSITION[profile_id]+POS_MONEY] + (data[PROFILE_START_POSITION[profile_id]+POS_MONEY+1] * 0x100)
+   #money_dec = int(money_hex, base=16)
+   return money_dec
+
+def set_money(data_object,profile_id, money_dec):
+   """ Using data, set the money given in decimal for the given profile_id. """
+   data = _get_data_from_data_object(data_object)
+   #money_bytes = _convert_dec_to_reverse_bytes(money_dec)
+   #pos_money_low = PROFILE_START_POSITION[profile_id]+POS_MONEY
+   data_bytearray = bytearray(data)
+   struct.pack_into('<i',data_bytearray,PROFILE_START_POSITION[profile_id]+POS_MONEY,money_dec)
+   data = bytes(data_bytearray)
+   print(f"after setting money to {money_dec}, we checked and got {get_money(data,profile_id)}")
+   return data
+
+def get_weapon(data_object,profile_id):
+   data = _get_data_from_data_object(data_object)
+   weapon = data[PROFILE_START_POSITION[profile_id]+POS_EQUIPPED_WEAPON]
+   return WEAPONS[weapon]
+
+def set_weapon(data_object,profile_id,weapon):
+   data = _get_data_from_data_object(data_object)
+   data_bytearray = bytearray(data)
+   weapon, weapon_name = get_weapon_info(weapon)
+   if weapon == -1:
+      ferror(f"Warning: cannot set weapon to {weapon}, because {weapon_name}")
+      return -1
+   # armed with weapon as the index number, let's change the savegame data
+   struct.pack_into('<i',data_bytearray,PROFILE_START_POSITION[profile_id]+POS_EQUIPPED_WEAPON,weapon)
+   data = bytes(data_bytearray)
+   print(f"after setting weapon to {WEAPONS[weapon]}, we checked and got {get_weapon(data,profile_id)}")
+   return data
+
+def get_weapon_info(weapon):
+   """ Returns index, and name of weapon, or -1 and "invalid" """
+   if type(weapon) == str:
+      try:
+         weapon_id = [index for index in range(len(WEAPONS)) if WEAPONS[index].lower() == weapon.lower()][0]
+         return weapon_id, WEAPONS[weapon_id]
+      except:
+         return -1, f"cannot find weapon {weapon}" # must be an incorrect name
+   elif type(weapon) == int:
+      if weapon not in range(0,16):
+         return -1, f"invalid index {weapon}; use 0-15" # must be <0 or >15
+      else:
+         return weapon, WEAPONS[weapon]
+   else:
+      return -1, f"invalid way to reference weapon: [{type(weapon)}]. Use index or name."
+
+def calculate_checksum(data):
+   """ Return the 4-byte checksum used by the game for the provided data. """
+   # aka # CRC-32/BZIP2
+   # The polynomial appears to be a standard one like used for Ethernet, but I am uncertain of the xor is standard or not.
+   # I learned all this only with <https://github.com/8051Enthusiast/delsum>
+   # crc width=32 poly=0x4c11db7 init=0x0 xorout=0x235b4b9c refin=false refout=false out_endian=little
+   csum = hex(crc_poly(data, 32, 0x4C11DB7, crc=0x0, ref_in=False, ref_out=False, xor_out=0x235b4b9c))
+   # comes in as ceb434d4, but needs to be d434b4ce, and bytearray is convenient way to swap it like that
+   # trim off the '0x' from the string
+   #print(f"Got csum={csum}")
+   csum = bytearray.fromhex(str(csum)[2:])
+   csum.reverse()
+   # and back to bytes because that is how we will want to use it.
+   return bytes(csum)
+
+def correct_file(filename, debuglevel = 0):
+   """ Given a savegame file, calculate the correct checksum and store that sum instead of whatever is there. """
+   cs, data = read_file(filename)
+   csum = calculate_checksum(data)
+   ran = False
+   if csum != cs:
+      if debuglev(5,debuglevel):
+         ferror(f"Stored checksum is {cs} and will update it to {csum}")
+      write_file(filename,csum,data)
+      ran = True
+   else:
+      if debuglev(2,debuglevel):
+         ferror(f"Stored checksum is still correct, {csum}. Skipping {filename}")
+   return ran