#!/bin/sh
# resize-uec-image

Usage() {
	cat <<EOF
Usage: ${0##*/} image size [output]
   Resize a UEC image to a new size.
   if output is given, do not modify 'image', but create new file 'output'

   New size is specified per resize2fs(8), e.g. "1G" for 1 gigabyte
EOF
	return 0
}

error() { echo "$@" 1>&2; }
fail() { [ $# -eq 0 ] || error "$@"; exit 1; }

human2bytes() {
   # converts size suitable for input to resize2fs to bytes
   # s:512 byte sectors, K:kilobytes, M:megabytes, G:gigabytes
   # none: block size of the image
   local input=${1} defunit=${2:-1024}
   local unit count;
   case "$input" in
      *s) count=${input%s}; unit=512;;
      *K) count=${input%K}; unit=1024;;
      *M) count=${input%M}; unit=$((1024*1024));;
      *G) count=${input%G}; unit=$((1024*1024*1024));;
      *)  count=${input}  ; unit=${2:-1024};;
   esac
   _RET=$((${count}*${unit}))
}

[ "$1" = "-h" -o "$1" = "--help" ] && { Usage; exit 0; }

[ $# -eq 3 -o $# -eq 2 ] || { Usage 1>&2; exit 1; }

old="$1"
size="$2"
new="${3:-${old}}"

human2bytes "${size}" && new_size=${_RET} ||
   fail "failed to understand ${size}"

if [ ! "${old}" -ef "${new}" ]; then
   file_out=$(file "${old}") || fail "failed to read ${old} with 'file'"
   case "${file_out}" in
      *gzip\ compressed*)
         zcat -f "$old" | cp --sparse=always /dev/stdin "$new";;
      *) cp --sparse=always "${old}" "${new}";;
   esac
   [ $? -eq 0 ] || fail "failed to cp ${old} -> ${new}"
fi

ls_out=$(ls -l "${new}") &&
   old_size=$(echo "${ls_out}" | awk '{print $5}') ||
   fail "failed to get size of ${new_img}"

e2fsck -fp "$new" || fail "failed to fsck ${new}"

if [ "${old_size}" -lt "${new_size}" ]; then
   truncate "--size=$size" "$new" || fail "failed to change size of ${new}"
fi

resize2fs "$new" "$size" || fail "failed to resize ${new} -> ${size}"

if [ "${old_size}" -gt "${new_size}" ]; then
   truncate "--size=$size" "$new" || fail "failed to change size of ${new}"
fi

exit 0