#!/bin/bash

: Usage: zfs-backup [filesystem] [destination_pool]

tmpdir="/export/home/tmp"

lockdir="/tmp/zfs-admin-lock"
if ! mkdir "$lockdir" >/dev/null 2>&1; then
  echo >&2 "ZFS admin lock directory is present."
  exit 1
fi

cleanup() { rm -rf "$lockdir"; }
trap cleanup EXIT

fs=$1
sourcepool=${1%%/*}
fsname=${1#*/}
destinationpool=$2

if ! zpool list -H "$sourcepool" >/dev/null 2>&1; then
  echo >&2 "The source pool, '$sourcepool' doesn't seem to exist."
  exit 1
fi

if ! zpool list -H "$destinationpool" >/dev/null 2>&1; then
  echo >&2 "The destination pool, '$destinationpool' doesn't seem to exist."
  exit 1
fi

if ! zfs list -H "$fs" >/dev/null 2>&1; then
  echo >&2 "The source filesytem, '$fs' doesn't seem to exist."
  exit 1
fi

printsnaps() {
sed 's,.*/,,' | awk '{print $1}' 
}

zfs list -rH -t snapshot $sourcepool/$fsname | printsnaps > /tmp/source-list
zfs list -rH -t snapshot $destinationpool/$fsname | printsnaps > /tmp/destination-list
diff -u /tmp/source-list /tmp/destination-list | grep -v '^+++' | awk '/^\+/ {print}' | sed "s,^\+,$destinationpool/," > /tmp/obsolete-snapshots
rm -f /tmp/source-list /tmp/destination-list

echo >&2 "Removing obsolete backups from the destination pool" 
for snapshot in $(cat /tmp/obsolete-snapshots); do
  echo >&2 "Removing '$snapshot' from destination."
  zfs destroy "$snapshot"
done

echo >&2 "Rolling back to the most recent snapshot on the destination." 
zfs rollback $(zfs list -rH -t snapshot $destinationpool/$fsname | awk '{snap=$1} END {print snap}')

echo >&2 "Calculating the most recent common snapshot between the two filesystems." 
common=""
if zfs list -H "$destinationpool/$fsname" >/dev/null 2>&1; then
  for snap in $(zfs list -rH -t snapshot "$destinationpool/$fsname" |
                  sed 's,.*@,,' | awk '{print$1}'); do
    if zfs list -rH -t snapshot "$fs" | sed 's,.*@,,' | awk '{print$1}' | grep "^${snap}$" >/dev/null 2>&1; then
      common=$snap
    fi
  done
fi

base=$common
foundcommon=false
if [ -z "$common" ]; then
  foundcommon=true
fi

for snap in $(zfs list -rH -t snapshot "$fs" |
                sed 's,.*@,,' | awk '{print$1}'); do
  if [ "$snap" = "$common" ]; then
    foundcommon=true
    continue
  fi

  if $foundcommon; then
    if [ -z "$base" ]; then
      echo >&2 "Sending '$1/$snap'"
      zfs send "$1@$snap" > $tmpdir/zfs.part
      mv $tmpdir/zfs.part $tmpdir/zfs.data
      zfs recv "$destinationpool/$fsname" < $tmpdir/zfs.data
      rm -f $tmpdir/zfs.data
      zfs set readonly=on "$destinationpool"
      zfs set atime=off "$destinationpool"
      zfs set sharenfs=off "$destinationpool"
      zfs set mountpoint=legacy "$destinationpool"
      zfs unmount "$destinationpool/$fsname"
      zfs rollback "$destinationpool/$fsname@$snap"
    else
      echo >&2 "Sending '$1@$base' -> '$1/$snap'"
      zfs send -i "$1@$base" "$1@$snap" > $tmpdir/zfs.part
      mv $tmpdir/zfs.part $tmpdir/zfs.data
      zfs recv "$destinationpool/$fsname" < $tmpdir/zfs.data
      rm -f $tmpdir/zfs.data
      # zfs unmount "$destinationpool/$fsname"
      # zfs rollback "$destinationpool/$fsname@$snap"
    fi
    base=$snap
  fi
done

true