#!/bin/bash
#
# bak - a simple rsync backup script
# Copyright (C) 2011 Clifton L. Snyder <cliff.snyder@gmail.com>
#
# 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.

# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software Foundation,
# Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
#
usage="usage: $0 [options] action"
usage=$usage'
options:
 -f FILE          path to config file (default: /etc/bak/bak.conf)
 -s, --source DIR source directory
 -t, --target DIR target directory
 -q, --quiet      suppress non-error messages
 -v, --verbose    turn on verbose logging
 -d, --debug      turn on debugging output
 -h, --help       display a brief help message and exit
actions:
 ls  list the current backups (default)
 do  perform a backup
 rm  remove a backup (UNIMPLEMENTED)
'
# TODO make running as an alternate user work
# -u, --user user run as user
# TODO implement retention (as of now: "infinite retention")
# -r, --retention  number of copies to keep
# TODO make 'do' the default action?

# default output: (relatively) quiet with no debugging
# 0: quiet; 1: verbose; 2: debug
LOG_LEVEL=0 

### default config options

config="/etc/bak/bak.conf"
# TODO implement retention (as of now: "infinite retention")
# retention=30
# TODO make running as an alternate user work
# user="$USER"
rsync="/usr/bin/rsync"
# some options from http://www.sanitarium.net/golug/rsync_backups_2010.html
#   check there for more detail
# TODO research --hard-links
# TODO research --inplace
# TODO research --numeric-ids
# TODO include support for includes/excludes?
# TODO include the option to not cross filesystem boundaries?
# TODO include interactive options --progress and --itemize-changes?
rsync_opts="--archive --hard-links --inplace --numeric-ids --delete"

# default action: ls
ACTION="ls"

# su="/bin/su"
# su_args="-c"

function error(){
    echo error: "$@" 1>&2
    echo -n "$usage" 1>&2
    exit 1
}

# preserve args (in case of -u)
# ARGV="$@"

### parse command line args

while [ -n "$1" ] ; do
    case "$1" in
	-f)
	    [[ -z "$2" ]] && error "$1 takes a FILE argument"
	    shift
	    config="$1"
	    [[ ! -f "$config" ]] && error "config file '$config' not found"
	    ;;
# TODO make running as an alternate user work
#	-u|--user)
#	    shift
#	    [[ -z "$1" ]] && error "-u takes a user as an argument"
#	    id "$1" >& /dev/null
#	    [[ ! "$?" -eq 0 ]] && error "user '$1' does not exist"
#	    user="$1"
#	    ;;
# TODO implement retention (as of now: "infinite retention")
#	-r|--retention)
#	    [[ -z "$2" ]] && error "$1 takes a NUM argument"
#	    shift
#	    retention="$1"
#	    ;;
	-s|--source) 
	    [[ -z "$2" ]] && error "$1 takes a DIR argument"
	    shift
	    source_dir="$1"
	    ;;
	-t|--target) 
	    [[ -z "$2" ]] && error "$1 takes a DIR argument"
	    shift
	    target_dir="$1"
	    ;;
	# log options; we'll use the highest specified log level
	-q|--quiet) [[ "$LOG_LEVEL" -lt 1 ]] && LOG_LEVEL=0;;
	-v|--verbose) [[ "$LOG_LEVEL" -lt 1 ]] && LOG_LEVEL=1;;
	-d|--debug) LOG_LEVEL=2;;
	-h|--help) echo -n "$usage"; exit 0;;
	do|ls|rm) ACTION="$1";;
	*) error "unknown option $1";;
    esac
    shift
done

# TODO make running as an alternate user work
# if the -u option differs from $USER, use su to run it as $user
# if [[ ! "$user" = "$USER" ]] ; then
#     [[ "$LOG_LEVEL" -ge 1 ]] && echo "running as $user"    
#     "$su $su_args" "'$0 $ARGV'"
#     exit $?
# fi

[[(-f "$config" && "$LOG_LEVEL" -ge 1)]] && echo "using config file $config"
[[ -f "$config" ]] && source "$config"

### let's make sure we have enough information to get started

# make sure we've got a legit source dir
[[ -z "$source_dir" ]] && error "source directory unspecified"
[[ -d "$source_dir" ]] || error "source directory '$source_dir' doesn't exist"
# generate a canonical path for our source directory
source_dir=`readlink -f $source_dir`
[[ "$LOG_LEVEL" -ge 1 ]] && echo "using source dir $source_dir"
# make sure we've got a legit target dir
[[ -z "$target_dir" ]] && error "target directory unspecified"
[[ -d "$target_dir" ]] || error "target directory '$target_dir' doesn't exist"
# generate a canonical path for our target directory
target_dir=`readlink -f $target_dir`
[[ "$LOG_LEVEL" -ge 1 ]] && echo "using target dir $target_dir"
# TODO check retention var for inappropriate value

# append some logging options to rsync
[[ "$LOG_LEVEL" -ge 2 ]] && rsync_opts="$rsync_opts -vv"
[[ "$LOG_LEVEL" -eq 1 ]] && rsync_opts="$rsync_opts -v"
[[ "$LOG_LEVEL" -eq 0 ]] && rsync_opts="$rsync_opts -q"

### let's figure out some things about where we're backing up

# first, we need to find the latest available copy in $target_dir
dirs=`find $target_dir -maxdepth 1 -mindepth 1 -type d | sort -n`
# let's track a few variables that might be useful
newest=0 # `date +%s -d '1970-01-01 00:00:00 UTC'` # oldest possible date
newest_dir=""
[[ "$LOG_LEVEL" -ge 2 ]] && echo "starting with '$newest' as the newest possible date"
oldest=`date +%s` # "now"
oldest_dir=""
[[ "$LOG_LEVEL" -ge 2 ]] && echo "starting with '$oldest' as the oldest possible date"
count=0
if [ -z "${dirs}" ] ; then
    # if we're working with an empty target directory we needn't worry about it
    count=0
    [[ "$LOG_LEVEL" -ge 1 ]] && echo "empty target directory"
else
    # otherwise, we have to determine which is the latest available copy
    [[ "$LOG_LEVEL" -ge 1 ]] && echo "non-empty target directory"
# TODO make this more resillient to garbage dirs being in the target
    for dir in $dirs; do
	let count=$count+1
	[[ "$LOG_LEVEL" -ge 2 ]] && echo "incremented target dir count to $count"
	d=`basename $dir`
	# d=`date +%s -d $b`
	# is this directory older?
	if [ $d -lt $oldest ] ; then
	    oldest=$d
	    oldest_dir=$dir
	    [[ "$LOG_LEVEL" -ge 2 ]] && echo "new oldest target dir: $oldest"
	fi
	# is this directory newer?
	if [ $d -gt $newest ] ; then
	    newest=$d
	    newest_dir=$dir
	    [[ "$LOG_LEVEL" -ge 2 ]] && echo "new newest target dir: $newest"
	fi
    done
    [[ "$LOG_LEVEL" -ge 1 ]] && echo "oldest target: $oldest"
    [[ "$LOG_LEVEL" -ge 1 ]] && echo "newest target: $newest"
    [[ "$LOG_LEVEL" -ge 1 ]] && echo "target count: $count"
fi

### all our vars should be set now, it's time to do perform our action

case $ACTION in
    ls) # list the current backups
	for dir in $dirs; do
	    d=`basename $dir`
	    date=`date --date "Jan 1, 1970 00:00:00 +0000 + $d seconds"`
	    echo $d "($date)"
	done
	;;
    do) # perform a backup
	now=`date +%s`
	td="$target_dir/$now"
	# make sure the new target doesn't already exist
	[[ -d "$td" ]] && error "target directory $td already exists"
	[[ "$LOG_LEVEL" -ge 1 ]] && echo "creating $td"
	mkdir -p "$td"
	# add link-dest if there are previous targets 
	if [ $count -gt 0 ] ; then
	    [[ "$LOG_LEVEL" -ge 2 ]] && echo "link-dest: $newest_dir/"
	    rsync_opts="$rsync_opts --link-dest=$newest_dir/"
	fi
	[[ "$LOG_LEVEL" -ge 2 ]] && echo "$rsync $rsync_opts $source_dir/ $td/"
	# perform the actual rsync
	$rsync $rsync_opts $source_dir/ $td/
	;;
    rm) # remove a backup
	echo "rm action UNIMPLEMENTED!"
# TODO implement rm action
# TODO implement a restore action?
	;;
    *) error "unknown action '$ACTION'";;
esac

# TODO implement a "cleanup" step (important for implementing retention)