#!/usr/bin/env zsh

set -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=$(date "+%Y%m%d%H%M")
depth=${#${(s./.)what}}
snaps=$(zfs list -t snap -d $depth -o name -H | grep $what | sort -nr)
snaps=(${(f)snaps})
latest=${snaps[1]}
latest_filename=${latest:gs#/#%}

case $action in
    snap-initial)
        zfs snap -r $what-$now
        print $what-$now
        ;;
    snap)
        [[ -n $latest ]]
        [[ "$what-$now" != $latest ]]
        zfs snap -r $what-$now
        print $what-$now
        ;;
    sync-initial)
        dst=$3
        [[ -d $dst ]] || usage
        setopt PIPE_FAIL
        zfs send -Rv $latest | zstd | ${=enccmd} > \
            $dst/$latest_filename.zfs.zst.gpg
        sync
        touch $dst/$latest_filename.from
        ;;
    sync)
        dst=$3
        [[ -d $dst ]] || usage
        latest_dst=($dst/*(.Onn[1]))
        [[ $latest_dst ]]
        latest_dst=${latest_dst[1]}
        latest_dst=${${latest_dst##*/}%.from}
        [[ $latest_dst != $latest_filename ]]
        setopt PIPE_FAIL
        zfs send -Rv -i ${latest_dst:gs#%#/} $latest | zstd | ${=enccmd} > \
            $dst/$latest_filename.zfs.zst.gpg
        sync
        print $latest_dst > $dst/$latest_filename.from
        ;;
    clean)
        count=$3
        [[ -n $count ]] || usage
        count=$(( $count + 1 ))
        for snap in $snaps ; do
            count=$(( $count - 1 ))
            [[ $count -le 0 ]] || continue
            zfs destroy -Rv $snap
        done
        ;;
    *)
        usage
        ;;
esac