#!/bin/bash

# Remove junk bytes from AVM image files (http://freetz.org/ticket/1614)
# Author: Alexander Kriegisch (http://scrum-master.de)

INPUT_FILE="$1"
OUTPUT_FILE="$2"
SFK_TOOL="$(dirname "$0")/sfk"
HEADER_MAGIC_HEX="3C1A8000375A038003400008"
INTRA_MAGIC_TXT="NMI Boot"
INTRA_MAGIC_HEX="4E4D4920 426F6F74"

if [ $# -ne 2 -o ! -e "$INPUT_FILE" ]; then
	echo "Usage: ${0##*/} input.image output.image"
	exit 2
fi

hexdumps="$("$SFK_TOOL" hexfind "$INPUT_FILE" -bin /$HEADER_MAGIC_HEX/ -quiet -context=32)"
offsets=($(echo "$hexdumps" | sed -nr 's/.*hit at offset 0x(.*)/\1/p'))

count=${#offsets[@]}
case $count in
	0) echo "No junk header found" >&2; exit 1 ;;
	1) echo "Junk header found, inspecting ..." ;;
	*) echo "Multiple junk headers found, inspecting ..." ;;
esac

for (( i=0; i<count; i++ )); do
	offs=${offsets[i]}

	case "$offs" in
		BE0000)
			junkver=1
			img_size_junk=$(echo "${hexdumps[i]}" | sed -rn "s/^.(.{8}) .{8} ${INTRA_MAGIC_HEX}.*/\1/p" )
			img_size_file=$(printf "%08X\n" $(( $(stat -c %s "$INPUT_FILE") -  256 - 8 )))
			;;
		BE0004)
			junkver=2
			img_size_junk=$(echo "${hexdumps[i]}" | grep -b1 "$INTRA_MAGIC_HEX" | head -n1 | sed -rn "s/^.* (.{8})< .*/\1/p" )
			img_size_file=$(printf "%08X\n" $(( $(stat -c %s "$INPUT_FILE") - 4096 - 8 )))
			;;
		*)
			echo "Junk header not valid, unexpected offset 0x$offs" >&2
			continue
			;;
	esac
	echo "Junk header found at V$junkver offset 0x$offs"

	if [ "$img_size_junk" != "$img_size_file" ]; then
		echo "Image size encoded in junk block does not match real file size"
		continue
	fi
	echo -n "Image size encoded in junk block matches real file size, removing junk bytes ... "
	head -c $((0x$offs)) "$INPUT_FILE" > "$OUTPUT_FILE"
	tail -c $((0x${img_size_file} - 0x$offs + 8)) "$INPUT_FILE" >> "$OUTPUT_FILE"
	echo "done."
	exit 0
done

echo "No junk bytes found" >&2
exit 1