#!/usr/bin/env sh
set -e

HOWROOT="${HOWROOT:-$(dirname "$(readlink -f "$0")")}"

if [ ! -d "$HOWROOT" ]; then
    echo "$HOWROOT is not a directory!" >&2
    exit 1
fi

{ [ "$1" ] && [ "$2" ]; } \
|| { eval "echo \"$(cat "$HOWROOT/USAGE")\"" && exit 0; }

. "$HOWROOT/lib/log.sh"

pkg="$1"
ver="$2"
tgt="$3"

if [ "$tgt" ] && [ ! -d "$tgt" ]; then
    echo "$tgt isn't a directory!" >&2
    exit 1
fi

{ vercmp formats | grep -q "^$pkg"; } \
&& fmt="$pkg" \
|| fmt="default"

[ ! -d "$HOWROOT/pkg/$pkg/default" ] || layers="$HOWROOT/pkg/$pkg/default:"

if [ -d "$HOWROOT/pkg/$pkg" ]; then
    layers="$(ls -d $HOWROOT/pkg/$pkg/*/ \
    | rev | cut -d/ -f2 | rev \
    | shsort "vercmp -f $fmt" \
    | while read dir; do
        [ "$dir" ] || continue;
        [ "$dir" != "default" ] || continue;

        if [ "$(vercmp -f "$fmt" "$dir <= $ver")" = "yes" ]; then
            printf "$HOWROOT/pkg/$pkg/$dir:"
        fi

    done)$layers"
fi

[ "$tgt" ] || { echo "$layers$HOWROOT/default" && exit 0; }

# mounting an overlayfs fails if only given a single lower directory, so use a
# read-only bind mount if just mounting the default scripts directory.  the
# behaviour of a read-only bind mount should be roughly equivalent to an
# overlayfs mounted with a single lower directory and no upper directory. (the
# only difference which comes to mind is that a bind mount does not count
# against overlayfs' nesting limit.)
if [ "$layers" ]; then
    mount -t overlay -o lowerdir="$layers$HOWROOT/default" none "$tgt"
else
    mount -o ro,bind "$HOWROOT/default" "$tgt"
fi