#!/bin/sh

# HOWTO restic
# 1a. init repository (sftp backend)
# restic -r sftp:user@host:restic-repo init
# 1b. init repository (local backend)
# restic -r /srv/restic-repo init
# 2. backup
# restic -r /srv/restic-repo --verbose backup ~/work
# 3. restore
# restic -r /srv/restic-repo restore 79766175 --target /tmp/restore-work
# list snapshots
# restic -r /srv/restic-repo snapshots
# filter by path
# restic -r /srv/restic-repo snapshots --path="/srv"
# integry check
# restic -r /srv/restic-repo check
# snapshot deletion policy
# restic -r /srv/restic-repo forget -d 31 -w 26 -m 24
# clean up unreferenced blocks
# restic -r /srv/restic-repo prune

# name of the temporary zfs snapshot.
SNAPNAME="backup"

# restic reads these, so we don't need the -r and -p parameters
export RESTIC_PASSWORD_FILE="$HOME/.restic_password"
export RESTIC_REPOSITORY="sftp:uugrn@uugrn.backup.haufe.it:uugrn-backup"

# read the zfs snapshot list (takes some time)
zfs list | cut -w -f1,5 | grep -v NAME | \
while read VOLUME
do
    NAME=$(printf "$VOLUME" | cut -w -f1)
    MOUNTPOINT=$(printf "$VOLUME" | cut -w -f2)
    
    # only backup mounted zfs volumes
    if [ "$MOUNTPOINT" == "none" ]; then
        printf "%s\n" "Volume $NAME not mounted. Not backing up."
    else

        # Listing and searching for a snaptshot takes MUCH longer than
        # simply trying to delete it.
        printf "%s\n" "Delete Leftover Snapshot: $NAME@$SNAPNAME"
        zfs destroy "$NAME@$SNAPNAME"

        # create zfs snapshot to freeze data for a moment
        printf "%s\n" "Creating Snapshot: $NAME@$SNAPNAME"
        zfs snap "$NAME@$SNAPNAME"
        
        # backup zfs snapshot directory with restic
        # (reason: does not need zfs to be restored)
        printf "%s\n" "Transferring Snapshot: $NAME@$SNAPNAME"
        restic backup "$MOUNTPOINT/.zfs/snapshot/$SNAPNAME/" --exclude-caches || exit
        
        # delete the temporary zfs snapshot
        printf "%s\n" "Deleting Snapshot: $NAME@$SNAPNAME"
        zfs destroy "$NAME@$SNAPNAME"
    fi
done

# restic forget "deletes" snapshots that do not match the specs
# however it leaves the data alone. The data is now unreferenced,
# but can still be used for deduplication.
printf "%s\n" "Dereference Outdated Backups:"
restic forget --keep-daily=31 --keep-weekly=26 --keep-monthly=24

# restic prune cleans up the unreferenced data and therefore frees 
# up space on the backup device
printf "%s\n" "Prune Backups:"
restic prune

# list current list of restic snapshots (informational, not needed)
printf "%s\n" "List Restic Backups:"
restic snapshots