#!/bin/sh -efu

fatal() {

	echo "$*" >&2

	exit 1

}

pkg="$1"

[ -n "$pkg" -a -e "$pkg" ] ||

	fatal "No package supplied"

_dd() {

	local o="$1"; shift

	dd if="$pkg" skip="$o" iflag=skip_bytes status=none $*

}

calcsize() {

	offset=$(($1 + 8))

	local i b b0 b1 b2 b3 b4 b5 b6 b7

	i=0

	while [ $i -lt 8 ]; do

		b="$(_dd $(($offset + $i)) bs=1 count=1)"

		[ -z "$b" ] &&

			b="0" ||

			b="$(exec printf '%u\n' "'$b")"

		eval "b$i=\$b"

		i=$(($i + 1))

	done

	rsize=$((8 + ((($b0 << 24) + ($b1 << 16) + ($b2 << 8) + $b3) << 4) + ($b4 << 24) + ($b5 << 16) + ($b6 << 8) + $b7))

	offset=$(($offset + $rsize))

}

case "$(_dd 0 bs=8 count=1)" in

	"$(printf '\355\253\356\333')"*) ;; # '\xed\xab\xee\xdb'

	*) fatal "File doesn't look like rpm: $pkg" ;;

esac

calcsize 96

sigsize=$rsize

calcsize $(($offset + (8 - ($sigsize % 8)) % 8))

hdrsize=$rsize

case "$(_dd $offset bs=3 count=1)" in

	"$(printf '\102\132')"*) _dd $offset | bunzip2 ;; # '\x42\x5a'

	"$(printf '\037\213')"*) _dd $offset | gunzip  ;; # '\x1f\x8b'

	"$(printf '\375\067')"*) _dd $offset | xzcat   ;; # '\xfd\x37'

	"$(printf '\135\000')"*) _dd $offset | unlzma  ;; # '\x5d\x00'

	"$(printf '\050\265')"*) _dd $offset | unzstd  ;; # '\x28\xb5'

	*) fatal "Unrecognized rpm file: $pkg" ;;

esac