#!/bin/bash

set -Eeuo pipefail
trap on_error SIGINT SIGTERM ERR

ScriptFullname=$(readlink -e "$0")
ScriptName=$(basename "$0")
TargetFile=""
BackupFile=""

function show_help ()
{
	echo "Usage:"
	echo "${ScriptName} FILENAME [BACKUPNAME]    patch specified kf2 executable"
	echo "${ScriptName} -h, --help               show help"
	echo ""
	echo "Dependencies: dd, readelf, hexdump"
}

function on_error ()
{
	trap - SIGINT SIGTERM ERR
	echo "Process aborted."
	restore
}

function backup ()
{
	if [[ -z "$BackupFile" ]]; then
		BackupFile="$TargetFile.orig"
	fi
	cp -f "$TargetFile" "$BackupFile"
}

function restore () 
{
	if [[ -z "$BackupFile" ]]; then
		BackupFile="$TargetFile.orig"
	fi
	if [[ -e "$BackupFile" ]]; then
		mv -f "$BackupFile" "$TargetFile"
		echo "Original executable restored"
	fi
}

function real_offset () # $1: offset (hex)
{
	local Offset="$1"
	local LoadAddr=$(
		readelf -l -W "$TargetFile" | \
		grep -P 'LOAD\s+0x000000' | \
		awk '{ print $3 }' | \
		grep -Po '[1-9a-f][0-9a-f]+')
	echo $((16#$Offset - 16#$LoadAddr))
}

function target_addr ()
{
	echo $(real_offset $(readelf -s -W "$TargetFile" | \
		grep -P 'KFGameInfo\w+SetGameUnranked' | \
		grep -v 'exec' | \
		head -n 1 | \
		awk '{ print $2 }' | \
		grep -Po '[1-9a-f][0-9a-f]+'))
}

function patched ()
{
	local ControlHex=$(
		hexdump -ve '1/1 "%.2x"' \
		-s $(target_addr) \
		-n 1 "$TargetFile")
	test "$ControlHex" == "c3" 
}

function apply_patch ()
{
	printf '\xc3' | \
		dd of="$TargetFile" \
		bs=1 \
		seek=$(target_addr) \
		count=1 \
		conv=notrunc 
	echo "Successfully patched!"
}

function main ()
{
	if ! [[ -w "$TargetFile" ]]; then
		echo "Can't write file. Make sure the file exists and it's read/write accessible."
		exit 1
	fi
	
	if patched; then
		echo "File already patched - skip."
		exit 0
	fi
	
	backup && apply_patch
}

if [[ $# -eq 0 ]]; then show_help; exit 0; fi
case $1 in
	  -h|--help ) show_help      ;      ;;
	    *       ) TargetFile="$1"; BackupFile="$2"; main ;;
esac