#!/bin/sh

# Perform incremental backups using rsync and hardlinks.
#
# Thanks to http://www.sanitarium.net/golug/rsync_backups_2010.html for the
# idea.

# Copyright (C) 2011-2014  Simon Ruderich
#
# This program 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
# (at your option) any later version.
#
# This program 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 program.  If not, see <http://www.gnu.org/licenses/>.


set -e

if test "$#" -lt 2; then
    echo "Usage: $0 <backups-directory> <arguments to rsync>" >&2
    echo
    echo "Note: The target directory is the _first_ argument!" >&2
    exit 2
fi


cd "$1" || exit 1
shift

# Get absolute path to last backup directory.
for x in backup-*; do
    test -d "$x" || continue
    dest="../$x" # relative to destination directory
done

target=backup-`date '+%Y-%m-%d-%H-%M-%S'`

if test -d current; then
    echo "Target directory 'current' already exists, aborting." >&2
    exit 1
fi

mkdir current
rsync \
    --verbose --itemize-changes --human-readable \
    --archive --hard-links --sparse --numeric-ids --one-file-system \
    --link-dest="$dest" \
    "$@" current \
|| {
    # Try to remove "current" without changing the exit code. In case the
    # connection failed without transferring any files, we want the next
    # backup to be able to run.
    code=$?
    rmdir current 2>/dev/null || true
    exit $code
}
mv current "$target"