#!/bin/zsh -e

usage() {
cat <<EOF
Usage: $0 DATASET@SNAPPREFIX snap-initial
       $0 DATASET@SNAPPREFIX snap
       $0 DATASET@SNAPPREFIX sync-initial DST
       $0 DATASET@SNAPPREFIX sync DST
       $0 DATASET@SNAPPREFIX clean COUNT
EOF
exit 1
}

enccmd="gpg --compress-level 0 --encrypt --recipient offline --cipher-algo AES-128"

[ $# -ge 2 ] || usage

what="$1"
action="$2"

now=$(date "+%Y%m%d%H%M")
snaps=$(zfs list -t snap -d 1 -o name -H | grep $what | sort -nr)
latest=$(echo $snaps | sed -n 1p)

case "$action" in
    snap-initial)
        zfs snap -r $what-$now
        echo $what-$now
        ;;
    snap)
        [ -n "$latest" ]
        [ "$what-$now" != "$latest" ]
        zfs snap -r $what-$now
        echo $what-$now
        ;;
    sync-initial)
        dst="$3"
        [ -d "$dst" ] || usage
        set PIPE_FAIL
        zfs send -Rv $latest | zstd | ${=enccmd} > $dst/$latest.zfs.zst.gpg
        sync
        touch $dst/$latest.from
        ;;
    sync)
        dst="$3"
        [ -d "$dst" ] || usage
        latest_dst=$(find $dst -type f -name "*.from" | sort -rn | sed -n 1p)
        [ -n "$latest_dst" ]
        latest_dst=$(basename ${latest_dst%.from})
        [ "$latest_dst" != "$latest" ]
        set PIPE_FAIL
        zfs send -Rv -i $latest_dst $latest | zstd | ${=enccmd} > $dst/$latest.zfs.zst.gpg
        sync
        echo "$latest_dst" > $dst/$latest.from
        ;;
    clean)
        count="$3"
        [ -n "$count" ] || usage
        count=$(( $count + 1 ))
        for snap in $(echo $snaps) ; do
            count=$(( $count - 1 ))
            [ $count -le 0 ] || continue
            zfs destroy -Rv $snap
        done
        ;;
    *)
        usage
        ;;
esac