#!/usr/bin/env bash
hooktype="$1"
backuppath="$2"
fstype="$(df --output=fstype / | sed 1d)"
function dellvm {
    umount ${backuppath}
    lvremove -y "$1"
}
function delbtrfs {
    btrfs subvolume delete ${backuppath}
}
if [[ "$fstype" == "btrfs" ]]; then
    if [[ -d ${backuppath} ]]; then
        delbtrfs
    fi
    if [[ "$hooktype" == "pre" ]]; then
        btrfs subvolume snapshot / ${backuppath}
    fi
else
    snapname=nixos_snap
    volume_group="$(mount | grep 'on / ' | cut -f 1 -d' ')"
    vgname="$(lvs --noheadings "$volume_group" -o vg_name | tr -d ' ')"
    snappath="/dev/mapper/${vgname}-${snapname}"
    if [[ -b "$snappath" ]]; then
        dellvm "$snappath"
    fi
    if [[ "$hooktype" == "pre" ]]; then
        lvcreate -l50%FREE -s -n "$snapname" "$volume_group"
        mount "$snappath" -o ro /backup/snapshot
    fi
fi