#!/usr/bin/zsh
set -eu
LAST_DAYS=30
LAST_MONDAYS=26
VOLS=(lcl/geofront lilith/sys magi/sys)

for vol (${VOLS}); do
  # Make a daily snapshot.
  /sbin/zfs snapshot -r -o nerv.local:timestamp=$(date '+%s') ${vol}@$(date '+%Y-%m-%d')

  # Keep last LAST_DAYS days worth of snapshots.
  xda=$(/bin/date -d "${LAST_DAYS} days ago" +%s)
  snaps=($(/sbin/zfs list -rHp -d1 -t snapshot -o nerv.local:timestamp,name -S nerv.local:timestamp ${vol} | grep -v '^-' | awk "\$1 < ${xda} { print \$2 }"))

  # Keep last LAST_MONDAYS Mondays.
  for i in $(/usr/bin/seq 1 ${LAST_MONDAYS}); do
    monday=$(/bin/date -d "Monday ${i} weeks ago" +%Y-%m-%d)
    snaps=(${snaps:#*@${monday}})
  done

  # Delete unnecessary snapshots.
  for s in $snaps; do
    case ${s} in
      ${vol}@20??-??-??)
        /sbin/zfs destroy -v -r ${s}
        ;;
      *)
        continue
        ;;
    esac
  done
done