#!/bin/bash

usage() {
    echo "USAGE: $0 [--clobber] [--verbose] [--] dir zfs-dir zfsdataset@old-snap [[zfsdataset]@new-snap]"
}

verbose=
debug() {
    if [ -n "$verbose" ]
    then
        echo "$@"
    fi
}

clobber=--no-clobber
while [ "${1:0:1}" == "-" ]
do
    case $1 in
        --)
            break
            ;;
        --verbose)
            verbose=true
            ;;
        --clobber)
            clobber=--force
            ;;
        --no-clobber)
            clobber=--no-clobber
            ;;
        *)
            >&2 echo "Unrecognized option: $1"
            usage
            exit 1
    esac
    shift
done

if (( $# < 3 ))
then
  usage
  exit 0
fi

root="$1"
prefix="$2"
old_snap="$3"
new_snap="$4"

if [[ "${root:0-1}" != "/" ]]
then
    root="$root/"
fi
if [[ "${prefix:0-1}" != "/" ]]
then
    prefix="$prefix/"
fi
echo "Target directory: $root"
echo "Source filesystem: $prefix"
echo "Old snapshot: $old_snap"
echo "New snapshot: $new_snap"

debug zfs diff -H "$old_snap" "$new_snap"
zfs diff -H "$old_snap" "$new_snap" | grep '^R' | grep -F -- "$prefix" | while read -r diffline
do
    get_path() {
        path="$(echo -e "$(echo "$diffline" | cut -d$'\t' "-f$1")")"
        echo "${path/#$prefix/$root}"
    }

    from="$(get_path 2)"
    to="$(get_path 3)"
    debug "From: $from"
    debug "To: $to"
    debug mv '"'"$from"'"' '"'"$to"'"'
    mkdir -vp -- "$(dirname "$to")"
    if [ -e "$to" ] && [ "$clobber" != "--force" ]
    then
        echo "File exists, not clobbering: $to"
    fi
    mv -v "$clobber" -- "$from" "$to" || echo "Unable to move $from"
done