#!/bin/sh
# backup garbage collector
# keep:
#   1 backup per year the previous years
hd=3600		# hour duration:  60s * 60
h12=43200	# 12h
dd=86400	# day duration:   hd * 24
wd=604800	# week duration:  dd * 7
md=2592000	# month duration: dd * 30
yd=31557600	# year duration:  dd * 365.25

now=$(date +%Y%m%d_%H%M%S)

date2ts() {
	t=$1; r=${t#????}; Y=${t%$r}
	t=$r; r=${t#??}; m=${t%$r}
	t=$r; r=${t#??}; d=${t%$r}
	t=${r#_}; r=${t#??}; H=${t%$r}
	t=$r; r=${t#??}; M=${t%$r}
	S=${t#??}
	date -d "$Y-$m-$d $H:$M:$S" +%s
}

# timestamp to date
ts2date() { date -d @$ts +%Y%m%d_%H%M%S; }

tsn=$(date2ts $now)

# minimal retention delay, according to age
retention_delay() {
	d=$(($tsn - $1))
	if (($d < $h12)); then R1=0
		# keep all backups in the last 12 hours
	elif (($d < $dd)); then R1=$hd
		# keep 1 backup per hour in the last day
	elif (($d < $wd)); then R1=$dd
		# keep 1 backup per day in the last week
	elif (($d < $md)); then R1=$wd
		# keep 1 backup per week in the last month
	elif (($d < $yd)); then R1=$md
		# keep 1 backup per month in the last year
	else R1=$yd
		# keep 1 backup per year in the previous years
	fi
	echo $R1
}

# sorted list of backups, most recent first
lbu=$(ssh bip ls -rv /home/backup/swift)
for d in $lbu; do
	tsc=$(date2ts $d)
	if ! [ "$tsp" ]; then
		echo keep $d
		tsp=$tsc
		continue
	fi
	mrd=$(retention_delay $tsp)
	dp=$(($tsp - $tsc))
	if (($dp < $mrd)); then
		echo "delete $d"
	else
		echo "keep $d"
		tsp=$tsc
	fi
done