#!/bin/sh

# tarsnap backup strategy. 20230317 pho@freebsd.org

# Keep 4 monthly, 4 weekly and 6 daily backups
# Handles missing backup days

set -eu
[ $# -eq 1 ] && now=$1 || now=`date +%s`
months=`date -u -j -f '%s' '+%Y%m' $now`
ndaily=6			# keep 6 daily backups
nmonthly=4			# Keep 4 monthly backups
nweekly=4			# Keep 4 weekly backups
paths=/Users/pho/work		# List of directories to backup
prefix=""			# backup file prefix
re='\d{8}T\d{6}W\d{2}'		# filename search pattern
tarsnap="/opt/local/bin/tarsnap --keyfile /var/root/tarsnap.key --cachedir /opt/local/tarsnap-cache"
tag=`date -j -f '%s' '+%Y%m%dT%H%M%SW%V' $now`
today=`date -j -f '%s' '+%Y%m%d' $now`
week=`date -j -f '%s' '+%V' $now`			# 1 - 53

echo "`date` Start of daily backup"
# Get a sorted list of the old backups. Newest first
list=`$tarsnap --list-archives | grep -E "$re" | sort -rn`

echo "$list" | grep -q $today && {
	echo "`date` Backup has already been run today"; exit 1; }

file=$prefix$tag.daily
echo "$list" | grep weekly | grep -q "W$week" ||
    file=$prefix$tag.weekly
echo "$list" | grep monthly | grep -q $months ||
    file=$prefix$tag.monthly

$tarsnap -c -f $file $paths ||  exit 2

# Remove old backups
list=`$tarsnap --list-archives | grep -E "$re" | sort -rn`

# daily
n=`echo "$list" | grep "daily" | wc -l`
j=1
for i in `echo "$list" | grep "daily"`; do
	if [ $j -gt $ndaily ]; then
		echo rm $i
		$tarsnap -d -f $i
	fi
	j=$((j + 1))
done

# weekly
n=`echo "$list" | grep "weekly" | wc -l`
j=1
for i in `echo "$list" | grep "weekly"`; do
	if [ $j -gt $nweekly ]; then
		echo rm $i
		$tarsnap -d -f $i
	fi
	j=$((j + 1))
done

# monthly
n=`echo "$list" | grep "monthly" | wc -l`
j=1
for i in `echo "$list" | grep "monthly"`; do
	if [ $j -gt $nmonthly ]; then
		echo rm $i
		$tarsnap -d -f $i
	fi
	j=$((j + 1))
done

list=`$tarsnap --list-archives | grep -E "$re" | sort -rn`
echo
echo "Current backups:"
echo $list | tr ' ' '\n' | grep daily
echo
echo $list | tr ' ' '\n' | grep weekly
echo
echo $list | tr ' ' '\n' | grep monthly
echo "`date` $file completed"
exit 0