#!/bin/bash -e

if test -e /etc/btrfs-snapshot.conf; then
    . /etc/btrfs-snapshot.conf
fi
if test -e ~/.btrfs-snapshot; then
    . ~/.btrfs-snapshot
fi

HOURLY_DEL=25
DAILY_DEL=8
WEEKLY_DEL=5
MONTHLY_DEL=
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=${DEL}
dryrun=0
periodity=${0%/*}
periodity=${periodity##*/}
if [[ $periodity =~ ^cron\... ]]; then
    periodity=${periodity#cron}
else
    periodity=
fi
case "$periodity" in
    (.hourly) del=${HOURLY_DEL};;
    (.daily) del=${DAILY_DEL};;
    (.weekly) del=${WEEKLY_DEL};;
    (.monthly) del=${MONTHLY_DEL};;
esac
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 <number> delete oldes snapshots beginning at <numbers>-th

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.

To create regular snapshots on a daily base, just run:

  sudo cp btrfs-snapshots.sh /etc/cron.daily/btrfs-snapshots

If btrfs-snapshots is run from a cron.daily, cron.hourly,
cron. monthly or cron.weekly directory, the periodity is automatically
appended to the snapshot name, and the expiry is set meaningfull:

  - hourly  → keep only 24 hours, --del 25
  - daily   → keep only 7 days, --del 8
  - weekly  → keep only 4 weeks, --del 5
  - monthly → old snapshots are not deleted

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 $0 --help" 1>&2
        exit 1
    fi
    shift
done
if test -n "${vols[*]}"; then
    BTRFS_VOLUMES="${vols[*]}"
fi

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
        if test "$subvol" = "/@"; then
            name=${subvol}
        else
            name=${subvol}-
        fi
    else
        if test "$fs" = "/"; then
            name="/"
        else
            name=${fs#/}
            name=${name%/}
            name=/${name//\//-}-
        fi
    fi
    date="-$(date +%Y-%m-%d-%H-%M)"
    target="${name}snapshot${periodity}"
    if test -n "$device"; then
        if mount | grep -q " on $TMP_MNT type "; then
            sudo umount "$TMP_MNT"
        fi
        sudo mount "$device" "$TMP_MNT"
        if test $dryrun -eq 1; then
            echo -e "→ \e[1mbackup ${subvol:+subvol $subvol of }$fs on $device\e[0m"
            echo " " mount "$device" "$TMP_MNT"
            echo " " btrfs subvolume snapshot "${TMP_MNT}${subvol}" "${TMP_MNT}${target}${date}"
            if test -n "$del"; then
                for f in $(ls -d1 "${TMP_MNT}${target}"-* | sort -r | tail -n +"$del"); do
                    echo " " btrfs subvolume delete "$f"
                done
            fi
            echo " " umount "$TMP_MNT"
        else
            sudo btrfs subvolume snapshot "${TMP_MNT}${subvol}" "${TMP_MNT}${target}${date}"
            if test -n "$del"; then
                for f in $(ls -d1 "${TMP_MNT}${target}"-* | sort -r | tail -n +"$del"); do
                    sudo btrfs subvolume delete "$f"
                done
            fi
        fi
        sudo umount "$TMP_MNT"
    else
        echo "ERROR: no device found for $fs" 1>&2
        exit 2
    fi
done