#/usr/bin/env bash

share_volume="<zfs base-dataset>" # ex. /trunk
target_host="<user>@<target_host>" # ex. root@fileserver

keep_snaps=$((24*4))

for path in $(zfs list -o name -t filesystem -r "$share_volume" | tail -n +2)
do
        echo "=> Volume: $path";
        snapname=$(zfs list -t snapshot -o name,creation -s creation -d 1 "$path" | tail -n +2 | grep 'frequent' | tail -n 1 | awk '{print $1}' 2>&1)
        dataset=$(echo $snapname | cut -d "@" -f 1)
        echo "Snapshot: $snapname"

        last_snapshot=$(ssh "$target_host" "(zfs list -o name -t filesystem -d 1 \"$path\" | tail -n +2) 2>&1")
        echo "Remote Filesystem: $last_snapshot"
        echo

        if [[ "$last_snapshot" =~ "dataset does not exist" ]]; then
                echo "- Dataset $dataset not found ... creating"
                zfs send $snapname | gzip | ssh "$target_host" "gzip -d | zfs recv \"$dataset\""
        else
                lastremote=$(ssh "$target_host" "(zfs list -t snapshot -o name,creation -s creation -d 1 $path | tail -n +2 | grep 'frequent' | tail -n 1 | awk '{print \$1}' | cut -d '@' -f 2) 2>&1")
                echo "Last Remote: $lastremote"

                localref=$(zfs list "$dataset@$lastremote" | tail -n +2 | awk '{print $1}')

                if [ "$dataset@$lastremote" == "$snapname" ]; then
                        echo "Replication already up-to-date ... skipping"
                        echo
                        continue
                fi

                if [[ "$lastremote" =~ "no datasets available" ]]; then
                        echo "No Snapshot for reference found ... doing full replication"
                        zfs send "$snapname" | gzip | ssh "$target_host" "gzip -d | zfs recv -F \"$dataset\""
                else
                        echo "Doing incremental replication ..."

                        if zfs send -i "$lastremote" "$snapname" | gzip | ssh "$target_host" "gzip -d | zfs recv -F \"$dataset\""
                        then
                                echo "Replicated successfully"
                        else
                                echo "!! Failed! ... continuing"
                                continue
                        fi
                fi
        fi

        echo "Cleanup remote snapshots (keep last $keep_snaps) ..."
        ssh "$target_host" "zfs list -t snapshot -d 1 \"$path\" | grep frequent | sort -r | tail -n \"+$keep_snaps\" | sort -r | awk '{print \$1}'| xargs -I {} bash -c 'echo \"Destroying \$1\"; zfs destroy \"\$1\";' _ {}"

        echo
done

echo "DONE"