#!/usr/bin/env python3

import sys, os
import shutil

def perform_ips_patch(patch_file, base_file, output_file, ips32):
	# IPS32 features not yet implemented
	magic = patch_file.read(5)
	if magic != b"PATCH":
		print("Invalid ips patch!")
		return -1

	shutil.copyfile(base_file, output_file)
	output_file = open(output_file, "rb+")

	offset = patch_file.read(3)
	while offset != b"EOF":
		offset = (int(offset[0]) << 16) + (int(offset[1]) << 8) + int(offset[2])
		length = patch_file.read(2)
		length = (int(length[0]) << 8) + int(length[1])
		output_file.seek(offset)
		if length != 0: # Normal mode
			data = patch_file.read(length)
			output_file.write(data)
		else: # RLE Mode
			count = patch_file.read(2)
			count = (int(count[0]) << 8) + int(count[1])
			byte = patch_file.read(1)
			output_file.write(byte * count)
		offset = patch_file.read(3)
	return 0


if __name__ == '__main__':

	if len(sys.argv) < 4:
		print("Usage: ips.py <patch file> <base file> <output file> [ips32] \
			\nSpecifying anything for ips32 will result in it patching as if the patch format is ips32 instead of ips")
		exit()

	if not (os.path.exists(sys.argv[1]) and os.path.exists(sys.argv[2])):
		print("Warning: one of the input files does not exist")
		exit()

	patch_file	= open(sys.argv[1], "rb")

	perform_ips_patch(patch_file, sys.argv[2], sys.argv[3], len(sys.argv) > 4)