#!/bin/bash
##
 # Sync with remote server and create Btrfs snapshots
 #
 # This scripts uses rsync to sync remote directories with a local copy
 # After every successful sync a readonly Btrfs snapshot of this copy is
 # created
 #
 # This script requires root privileges for creating Btrfs snapshots.
 # Consider using public key authentification with SSH to allow root
 # logins on remote machines:
 #
 # On remote side:
 #  echo "PermitRootLogin without-password" >> /etc/ssh/sshd_config:
 #
 # On local side:
 #  sudo ssh-keygen
 #  sudo cat /root/.ssh/id_dsa.pub | ssh user@remote 'cat >> /root/.ssh/authorized_keys'
 #
 # @copyright   2013 Steffen Vogel
 # @license     http://www.gnu.org/licenses/gpl.txt GNU Public License
 # @author      Steffen Vogel <info@steffenvogel.de>
 # @link        http://www.steffenvogel.de
 ##
##
 # This script is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
 # the Free Software Foundation, either version 3 of the License, or
 # any later version.
 #
 # This script is distributed in the hope that it will be useful,
 # but WITHOUT ANY WARRANTY; without even the implied warranty of
 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 # GNU General Public License for more details.
 #
 # You should have received a copy of the GNU General Public License
 # along with this script. If not, see <http://www.gnu.org/licenses/>.
 ##

function usage {
        echo "Usage: $(basename $0) SOURCE DEST"
        echo
        echo "   SOURCE  a path to the subvolume to backup"
        echo "   DEST    a path to the backup destination"
        exit 1
}

set -e

if [ $# -ne 2 ]; then
	echo -e "invalid args!"
	echo
        usage
fi

DATE=$(date +%F_%H-%M-%S)

SRC=$1
DEST=$(readlink -f $2)

if ! btrfs sub show $DEST/.current &> /dev/null; then
	if [ -d $DEST/.current ]; then
		echo -e "destination directory exists and is not a valid btrfs subvolume!"
		echo
		usage
	else
		btrfs sub create $DEST/.current
	fi
fi

# rsync options
OPTS="--archive --acls --xattrs"
OPTS+=" --progress --human-readable"
OPTS+=" --delete --delete-excluded"
OPTS+=" --exclude /dev/"
OPTS+=" --exclude /proc/"
OPTS+=" --exclude /sys/"
OPTS+=" --exclude /tmp/"
OPTS+=" --exclude /run/"
OPTS+=" --exclude /mnt/"
OPTS+=" --exclude /media/"
OPTS+=" --exclude /lost+found/"

# sync with remote
rsync $OPTS $SRC $DEST/.current/

# create new readonly snapshot
btrfs subvolume snapshot -r $DEST/.current $DEST/$DATE

# create symlink to latest snapshot
ln -rsfT $DATE latest