#!/usr/bin/env bash

# rsyncshot
# convenient backups using rsync and hard links

# Craig Jennings <c@cjennings.net>
# Inspired by Mike Rubel: http://www.mikerubel.org/computers/rsync_snapshots/
# requirements: bash, rsync, flock, cron, grep
# - unix filesystem capable of hard links at destination
# - core unix utilities: rm, mv, cp, touch

# debugging: uncomment next 4 lines for debugging output
# exec 5> >(logger -t $0)
# BASH_XTRACEFD="5"
# PS4='$LINENO: '
# set -x

# default locations for setup
# modify MOUNTDIR to point to the mount point of your backup

#  ---------------------------- Constants ----------------------------

MOUNTDIR=/media/backup;
SCRIPTLOC=/usr/local/bin/rsyncshot;
DESTINATION=$MOUNTDIR/$HOSTNAME

INSTALLHOME=/etc/rsyncshot
LOGFILE=/var/log/rsyncshot.log;

INCLUDES="$INSTALLHOME/include.txt";
EXCLUDES="$INSTALLHOME/exclude.txt";

# copy, move, and rm commands have been aliased by the user or distro
# creator to require confirmation on certain actions.
# using variables allows us to sidestep any alias
CP="/usr/bin/cp"
MV="/usr/bin/mv"
RM="/usr/bin/rm"

# prevent overlapping runs with flock
FLOCKCHECK="flock -x /tmp/rsyncshot.lock -c"

# default cron job entries
CRON_Q="15,30,45 * * * * "; # every quarter-hour except minute 0
CRON_H="0 1-23 * * * ";     # hourly on minute 0 from 1am to 11pm
CRON_D="0 12 * * 1-6 ";     # daily at noon, monday - saturday
CRON_W="0 12 * * 7 ";       # weekly at noon on sundays

#  ------------------------ Utility Functions ------------------------

help()
{
    printf "\nrsyncshot - compact snapshots on Linux using rsync and hard links.\n\n"
    printf "Usage:\nrsyncshot <name> <number of backups to retain>\n"
    printf "          setup (installs rsyncshot and cron jobs)\n"
    printf "          help  (prints this info)\n"
    printf "Notes:\n"
    printf '%s\n'  "- rsyncshot must be run as root"
	printf '%s\n\n' "- install and log locations defined in script."
}

error()
{
	echo "ERROR: $0:" "$@" 1>&2;
    echo "See \"rsyncshot help\" for usage."
    exit 1;
}

setup()
{
    # copy this file to directory on path and make executable
	$CP -f "$0" "$SCRIPTLOC"
	sudo chmod +x "$SCRIPTLOC"
	echo "$0 copied to $SCRIPTLOC and made executable"

    # make install home if it doesn't exist;
    if [ ! -d $INSTALLHOME ]; then
	   mkdir -p $INSTALLHOME;
	   echo "Created install home at $INSTALLHOME";
    fi

    # create includes file and add default entries
    if [ -f $INCLUDES ]; then $RM $INCLUDES; fi
    printf "/home /etc /usr/local/bin" >> $INCLUDES;
    echo "modify include file at $INCLUDES";

    # create excludes file and add default entries
    if [ -f $EXCLUDES ]; then $RM $EXCLUDES; fi
    printf "*.pyc\n*.pyo\n*.class\n*.elc\n*.o\n*.tmp\n.cache*" >>  $EXCLUDES;
    echo "modify exclude file at $EXCLUDES";

	# write out current crontab, append default entries, and install
	touch "$LOGFILE"
	crontab -l > crontemp;
	{
		echo "$CRON_H $FLOCKCHECK '$SCRIPTLOC hourly 22 >> $LOGFILE 2>&1'"
		echo "$CRON_D $FLOCKCHECK '$SCRIPTLOC daily 6 >> $LOGFILE 2>&1'"
        echo "$CRON_W $FLOCKCHECK '$SCRIPTLOC weekly 51 >> $LOGFILE 2>&1'"
        echo "$CRON_Q $FLOCKCHECK '$SCRIPTLOC quarter-hour 3 >> $LOGFILE 2>&1'"
	} >> crontemp
    crontab crontemp;
    $RM crontemp;
    echo "hourly, daily, and weekly cron jobs installed.";
}

#  ----------------------------- Script ----------------------------

# uppercase for case-insensitivity
TYPE=$(tr '[a-z]' '[A-Z]' <<< $1);
if [ "$TYPE" = "HELP" ]; then help; exit; fi

# ensure we're running as root
if [ "$EUID" -ne 0 ]; then error "This script must be run as root."; fi

# display start information
echo "rsyncshot invoked on $(date -u) with: $0 $1 $2";

# if logfile was removed, recreate it.
[ ! -f "$LOGFILE" ] || touch "$LOGFILE"

# validate backup type
# first argument must be alpha characters
if ! [[ $1 =~ [a-zA-Z] ]]; then error "snapshot type not recognized."; fi
if [ "$TYPE" = "SETUP" ]; then setup; exit; fi

# validate max snapshots
# second argument must be numeric
if ! [[ $2 =~ [0-9] ]]; then error "max snapshots not a number."; fi
MAX=$(($2-1));

# validate include file (source directories) exist
# validates the include file exists, and checks the file contents are valid directories
if [ ! -f "$INCLUDES" ]; then error "include file $INCLUDES not found."; fi
SOURCES=$(<$INCLUDES);
for SOURCE in $SOURCES
do
    if [ ! -d "$SOURCE" ]; then error "source $SOURCE not found"; fi
done

# validate exclude file (exclusion patterns) exist
if [ ! -f "$EXCLUDES" ]; then error "Exclude file $EXCLUDES not found."; fi

[ -d $MOUNTDIR ] || error "$MOUNTDIR doesn't exist."

# if destination filesystem not mounted attempt mounting; error if attempt fails
if ! grep -qs "$MOUNTDIR" /proc/mounts >> /dev/null 2>&1; then
	mount "$MOUNTDIR" >> /dev/null 2>&1
	if ! grep -qs "$MOUNTDIR" /proc/mounts >> /dev/null 2>&1; then
		error "$MOUNTDIR not mounted and mount attempt failed."
	fi
fi

[ -d "$DESTINATION" ] || mkdir "$DESTINATION" || \
	error "$DESTINATION doesn't exist, and attempt to create directory failed."

# sync each backup directory in turn
for SOURCE in $SOURCES
do
    rsync -avh -i --times \
    	  --delete  --delete-excluded \
		  --exclude-from="$EXCLUDES" \
		  --update "$SOURCE" "$DESTINATION"/latest ;
done

# delete max+1 snapshot if it exists
if [ -d "$DESTINATION"/"$TYPE"."$MAX" ]; then
	$RM -rf "$DESTINATION"/"$TYPE"."$MAX";

fi

# rotate remaining snapshots descending
for (( start=$((MAX)); start>=0; start--)); do
	end=$((start+1));
	if [ -d "$DESTINATION"/"$TYPE".$start ]; then
		$MV "$DESTINATION"/"$TYPE".$start "$DESTINATION"/"$TYPE".$end;
	fi
done

# reset directory timestamp
touch "$DESTINATION"/latest

# hard link / copy to destination
$CP -al "$DESTINATION"/latest "$DESTINATION"/"$TYPE".0;

# make directory type read-only
chmod -w "$DESTINATION"/"$TYPE".0

# print time and exit
echo "rsyncshot completed $(date -u) ";
exit 0;