#!/bin/sh

set -e

export LYRROOT="$(dirname "$(readlink -f "$0")")"
export LYRREPO="${LYRREPO:-/usr/var/lyr}"

[ -n "$1" ] || { \
echo "
usage: $(basename $0) <command> <layer name>

commands:
    workdir
        returns the work directory path for the layer.

    upperdir
        returns the upper directory path for the layer.

    mountdir
        returns the mount directory path for the layer.

    mk
        create a new layer with the given name.

    rm
        unmount and delete the layer with the given name.

    up [<lower path>[:<lower path>]]
        mount the given layer with the given lower paths. print the mount path.

    dn
        unmount the given layer.
" && exit 0; }

# if this is running on an interactive
# terminal (as opposed to in a script), if tput is installed, and if tput
# knows some color codes, then set the color values.
if [ -t 1 ] && [ "$(tput colors 2>/dev/null || echo 0)" -ge 8 ]; then
    _clr="$(tput sgr0)"
    _blu="$(tput setaf 6)"
    _ylw="$(tput setaf 3)"
    _red="$(tput setaf 1)"
fi
log() { echo "$_blu[LOG]$_clr $@"; }
wrn() { echo "$_ylw[WRN]$_clr $@" >&2; }
err() { echo "$_red[ERR]$_clr $@" >&2; exit 1; }

case "$1" in
    workdir) echo "$LYRREPO/work/$2";;
    upperdir) echo "$LYRREPO/upper/$2";;
    mountdir) echo "$LYRREPO/mount/$2";;
    mk) mkdir -p "$LYRREPO/upper/$2";;

    rm)
        { ! mountpoint -q "$LYRREPO/mount/$2" || umount "$LYRREPO/mount/$2"; } \
        && rm -fr "$LYRREPO/upper/$2" "$LYRREPO/mount/$2" "$LYRREPO/work/$2"
        ;;

    up)
        [ -n "$3" ] && { layer="$3" && lower="$2"; } || layer="$2"
        work="$LYRREPO/work/$layer"
        upper="$LYRREPO/upper/$layer"
        mnt="$LYRREPO/mount/$layer"
        [ -d "$upper" ] || err "layer '$layer' not recognized!"

        mkdir -p "$work" "$mnt"

        if [ -n "$lower" ]; then
            mount -t overlay -o lowerdir=$lower,upperdir=$upper,workdir=$work \
            none "$mnt"
        else
            mount -o bind "$upper" "$mnt"
        fi

        echo "$mnt"
        ;;

    dn) umount "$LYRREPO/mount/$2" && rm -r "$LYRREPO/mount/$2";;
    *) err "unrecognized command '$1'";;
esac