#!/bin/sh

## rolling-backup.sh, v0.1
## Copyright (C) 2001, 2002 Gary Benson <gary@inauspicious.org>
##
## 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 2 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.

# Script to perform backups, 'rolling' in the sense that a number of
# older copies are kept as well.  Invoke (from cron or similar) with
# the name of a directory full of config files as the only argument.
#
# Config file directives:
#  FILE (mandatory) -- name of the file to save the backup as
#  CMD (mandatory),
#  ARGS (optional) -- "$CMD $ARGS" is the command to write the data to
#    be backed up to stdout.
#
# As an example, the entry I use to back up my diary on advogato.org is:
#
# --- cut here ---
# # rolling-backup config file to backup my diary on Advogato.
#
# FILE="$HOME/backups/advogato/diary.xml"
# CMD="wget"
# ARGS="-q -O - http://www.advogato.org/person/gary/diary.xml"
# --- stop cutting ---

###########################################################################

# Check the arguments
if [ $# != 1 ]; then
    echo 1>&2 "usage: $0 configdir"
    exit 1
fi

# Process all files in the supplied directory
for CONFIG in $1/*[^~]
do
    # Fill in the defaults, then source and check the configfile
    unset FILE CMD ARGS
    . $CONFIG || exit 1

    if [ "x$FILE" = "x" ]; then
	echo 1>&2 "mandatory option `FILE' not set"
	exit 1
    fi
    if [ "x$CMD" = "x" ]; then
	echo 1>&2 "mandatory option `CMD' not set"
	exit 1
    fi

    # Split $FILE
    pushd `dirname $FILE` > /dev/null || exit 1
    FILE=`basename $FILE`

    # Dump the data.
    TMP=`mktemp $FILE.XXXXXXXX` || exit 1
    $CMD $ARGS > $TMP || exit 1

    if [ ! -f $FILE ]
    then
	# This is the first backup ever: rename $TMP
	mv $TMP $FILE
    else
	# Only replace files if they have changed
	diff -q $TMP $FILE > /dev/null
	case $? in
	2)
	    exit 1
	    ;;
	0)
	    # No change
	    rm -f $TMP
	    ;;
	1)
	    # Changed
	    test -f $FILE.4 && rm -f $FILE.4
	    for i in 3 2 1
	    do
		test -f $FILE.$i && mv $FILE.$i $FILE.`expr $i + 1`
	    done
	    mv $FILE $FILE.1
	    mv $TMP $FILE
	    ;;
	*)
	    echo 1>&2 "diff returned $?"
	    exit 1
	esac
    fi

    popd >> /dev/null || exit 1
done

exit 0