#!/bin/bash -e

BTRFS_VOLUMES=${BTRFS_VOLUMES:-$(awk '!/^#/ && $3=="btrfs" {print $2}' /etc/fstab | tr '\n' ' ' | sed 's, $,,')}
TMP_MNT=${TMP_MNT:-/var/tmp/btrfs-backup}

vols=()
del=
dryrun=0
while test $# -gt 0; do
    case "$1" in
        (-h|--help) cat <<EOF
$0 [OPTIONS]

OPTIONS

  -h, --help         show this help
  -n, --dry-run      execute dry run, do not backup, just show commands
  -p, --path <path>  add a path that contains a btrfs (sub-) volume
                     (defaults to: ${BTRFS_VOLUMES})
  -m, --mnt <path>   temporary mount point (default: ${TMP_MNT})

not yet implemented:

  -d, --del <days>   delete snapshots older than given number of days

ENVIRONMENT

  BTRFS_VOLUMES      specify all volume pathes (instead of -p)
  TMP_MNT            temporary mount point (instead of -m)

DESCRIPTION

Creates a snapshot for all btrfs volumes specified. Snapshot is named
from the subvol name or if there is no subvol, from the path by
appending -snapshot-YYYY-MM-DD-HH-mm.

EOF
                    exit;;
        (-n|--dry-run) dryrun=1;;
        (-p|--path) shift; vols+=( "$1" );;
        (-m|--mnt) shift; TMP_MNT="$1";;
        (-d|--del) shift; del="$1";;
        (*) echo "ERROR: unknown option $1, try $0 --help" 1>&2
            exit 1;;
    esac
    if test $# -lt 1; then
        echo "ERROR: missing argument, try $0 --help" 1>&2
        exit 1
    fi
    shift
done

BTRFS_VOLUMES=${BTRFS_VOLUMES:-$(awk '!/^#/ && $3=="btrfs" {print $2}' /etc/fstab)}
TMP_MNT=${TMP_MNT:-/var/tmp/btrfs-backup}

test -d "${TMP_MNT}" || mkdir -p "${TMP_MNT}"
for fs in ${BTRFS_VOLUMES}; do
    device=$(mount | awk '$3=="'$fs'" && $5=="btrfs" {print $1}')
    subvol=$(mount | awk '$3=="'$fs'" && $5=="btrfs" {split(substr($6, 2, length($6)-2), res, ","); for (r in res) {if (res[r]~/^subvol=/) {sub(/^subvol=/,"" , res[r]); print res[r]}}}')
    if test -n "$subvol"; then
        name=${subvol}
    else
        if test "$fs" = "/"; then
            name="@root"
        else
            name=${fs#/}
            name=${name%/}
            name=${name//\//-}
        fi
    fi
    target="${name}-snapshot-$(date +%Y-%m-%d-%H-%M)"
    if test $dryrun -eq 1; then
        echo btrfs subvolume snapshot "${TMP_MNT}${subvol}" "${TMP_MNT}/${target}"
    else
        if mount | grep -q " on $TMP_MNT type "; then
            sudo umount "$TMP_MNT"
        fi
        sudo mount "$device" "$TMP_MNT"
        sudo btrfs subvolume snapshot "${TMP_MNT}${subvol}" "${TMP_MNT}/${target}"
        sudo umount "$TMP_MNT"
    fi
done