#!/usr/bin/env bash
set -eo pipefail

image="$1"; [ -z "$1" ] && { echo "No image file specified!" >&2; exit 1; }
mfile="$2"; [ -z "$2" ] && { echo "No mapfile specified!"    >&2; exit 1; }
[ -z "$3" -a -t 1 ] && { echo "The output of this script is unsafe for raw display." >&2
                         exit 1; } \
                    || ofile=${3:-/dev/stdout}

BLOCKSIZE=`sed -nE 's/^#BLOCKSIZE=([0-9]+)$/\1/p' "$mfile"`
[ -z "$BLOCKSIZE" ] && { echo "Mapfile does not specify blocksize!" >&2; exit 1; }

shopt -s expand_aliases
alias dd="dd bs=$BLOCKSIZE status=none"

{
i=0
while read -r -d$'\n' _ block lengt _; do
	#Leaves the remainder block for convenience
	dd if="$image"  skip=$i count=$((block-i))
	dd if=/dev/zero count=$((lengt-1))
	i=$((block+lengt-1))
done < <(grep -v ^\# "$mfile" | sed -En '/[a-f0-9]{64}/!p' | sort -unk2)
dd if="$image" skip=$i
} > "$ofile"