#!/bin/sh

set -e

die() { echo "$(basename "$0"): $1" && exit 1 ; }

# file check
! [ "$1" ]         && die "No file was specified"
! [ -f "$1" ]      && die "$1 is not a file"
# mountpoint check
! [ "$2" ]         && die "No mountpoint was specified"
! [ -d "$2" ]      && die "Mountpoint $2 is not a directory"
[ "`ls -A "$2"`" ] && die "Mountpoint $2 is not empty"
# check disk image validity
! fdisk -lu "$1" 2>&1 | grep -m1 "\s*Start\s*End" >/dev/null && die "File $1 is not a disk image"

# get sectorsize
#sectorsize=$(fdisk -lu "$1" | grep -m1 '^Units:' | cut -d' ' -f8)  # Sector size is 8th word
sectorsize=512

# get partition num, if there is more than one part, interactively if not available
# TODO check if there is no partitions
partition="$3"
if [ -z "$partition" ]; then
	fdisk -o Size,Type,Name -lu "$1" | awk '!f{print $0};f>0{print "  " f-1 ") " $0; f++};f==-1{print "Part " $0;f=1};/^$/{f=-1}'

	printf "\nChoose partition number to mount: "
	read partition
fi

# check if part num valid
[ -z "${partition##*[!0-9]*}" ] && die "Illegal number: '$partition'"

# get offset from fdisk
fdisk_ignore_lines=9  # ignore first 9 lines of output
offset=$(fdisk -o Start -l "$1" | sed $(( fdisk_ignore_lines + partition ))'q;d' )

# check if that produced a valid offset
[ -z "$offset" ] && die "Partition $partition does not exist"

# try to mount
mount -o loop,offset=$(( offset * sectorsize )) "$1" "$2" && echo "Successfully mounted" || die "Error mounting"