#/bin/bash

# Usage: replicate <hostname> <zfs filesystem>
remote=$1
remote_fs=$2
remote_pool=${2%%/*}

# Set this variable to '1' to use the legacy, non-marker, snapshot diff, replicate script logic
use_legacy_replicate=0

# Set the name of the local pool used to store the backup of the remote
local_pool=backups

# Make sure we have valid arguments
if [[ -z "$remote" ]] || [[ -z "$remote_fs" ]]; then
  echo "Usage: $0 <hostname> <zfs filesystem>"
  exit 1
fi

# Make sure the local pool and local receiving filesystem exist, or print some errors
if ! zpool list -H "$local_pool" >/dev/null 2>&1; then
  echo >&2 "-E- The local pool, '$local_pool' doesn't seem to exist."
  exit 1
fi
if ! zfs list "$local_pool/$remote_pool" >/dev/null 2>&1; then
  echo >&2 "-E- The local filesystem for the remote pool, '$local_pool/$remote_pool' doesn't seem to exist."
  echo >&2 "    You will need to create this filesystem before this script can replicate your data."
  echo >&2 "    You can create this filsystem by executing this command: 'zfs create $local_pool/$remote_pool'"
  exit 1
fi

# Obtain the zpool guid for the local pool
local_pool_guid=`zpool get guid $local_pool 2>&1 | grep $local_pool | awk '{ print $3 }'`
if ! zpool get guid $local_pool > /dev/null 2>&1; then
  echo >&2 "-E- Unable to extract the guid for the local pool: $local_pool"
  exit 1
fi

# Turn on shell verbosity
set -x

# Setup our backup marker names
current_backup_marker=${remote_fs}@current-backup-${local_pool_guid}
previous_backup_marker=${remote_fs}@previous-backup-${local_pool_guid}

# The ssh connection doesn't find zfs without this.
zfs=/usr/sbin/zfs

# List the snapshots on the remote machine.
remote_list=$(mktemp /tmp/replicate.XXXXXX)
ssh $remote \
    $zfs list -H -t snapshot |
    grep ^${remote_fs}@ |
    awk '{print$1}' > $remote_list
if [[ $? != 0 ]]; then
  echo "-E- remote $zfs list command failed"
  exit 1
fi

# List the snapshots on the local machine.
local_list=$(mktemp /tmp/replicate.XXXXXX)
$zfs list -H -t snapshot |
    grep ^${local_pool}/${remote_fs}@ |
    awk '{gsub(/^${local_pool}./,"",$1); print$1}' > $local_list
if [[ $? != 0 ]]; then
  echo "-E- local $zfs list command failed"
  exit 1
fi

if [ $use_legacy_replicate == 0 ]; then
  # Destroy the current backup marker snapshot on the remote system if it exists
  grep -q ${current_backup_marker} $remote_list
  if [ $? == 0 ]; then
    ssh $remote $zfs destroy ${current_backup_marker} 
    if [[ $? != 0 ]]; then
      echo "-E- remote $zfs destroy command failed"
      exit 1
    fi
  fi
  # Create the current backup marker snapshot on the remote system
  ssh $remote $zfs snapshot ${current_backup_marker}
  if [[ $? != 0 ]]; then
    echo "-E- remote $zfs snapshot command failed"
    exit 1
  fi

  # Check to see if the previous backup marker exists in the remote snapshot list.
  # Check to see if the previous backup marker exists in the local snapshot list.
  # If the previous backup markers exists, perform an incremental replicate.
  # Otherwise, perform a full replicate.
  grep -q ${previous_backup_marker} $remote_list
  full=$?
  grep -q ${previous_backup_marker} $local_list
  full=$(($full || $?))

  if [[ $full == 0 ]]; then
    ssh $remote $zfs send -R -I${previous_backup_marker} ${current_backup_marker} | 
        $zfs receive -vF -d ${local_pool}/${remote_fs%/*}
    if [[ $? != 0 ]]; then
      echo "-E- remote incremental $zfs send command failed"
      exit 1
    fi
  else
    ssh $remote $zfs send -R ${current_backup_marker} |
        $zfs receive -vF -d ${local_pool}/${remote_fs%/*}
    if [[ $? != 0 ]]; then
      echo "-E- remote full $zfs send command failed"
      exit 1
    fi
  fi
 
  # destroy the previous backup markers now that we've replicated past them
  $zfs destroy ${local_pool}/${previous_backup_marker} > /dev/null 2>&1
  ssh $remote $zfs destroy ${previous_backup_marker} > /dev/null 2>&1

  # Rename the current backup marker to be the previous backup marker
  $zfs rename ${local_pool}/${current_backup_marker} ${local_pool}/${previous_backup_marker}
  if [[ $? != 0 ]]; then
    echo "-E- local $zfs rename command failed"
    exit 1
  fi
  ssh $remote $zfs rename ${current_backup_marker} ${previous_backup_marker}
  if [[ $? != 0 ]]; then
    echo "-E- remote $zfs rename command failed"
    exit 1
  fi
   
else
  # See what the most recent snapshot on the remote end is.
  latest=$(tail -n 1 $remote_list)

  # I did this to make sure that diff would always display the most recent common
  # Since we're keying off the context of the diff, we need to ensure we will get context
  # by injecting a known difference in case no others exist in the lists.
  echo bogus.remote >> $remote_list
  echo bogus.local  >> $local_list
  common=$(diff -u $remote_list $local_list | grep '^ ' | tail -n 1)

  if [ -n "$common" ]; then 
    # We found a common snapshot
    ssh $remote $zfs send -R -I${common/*@/@} $latest |
        $zfs receive -vF -d ${local_pool}/${remote_fs%/*}
  else
    # We did not find a common snapshot, so send the entire filesystem
    ssh $remote $zfs send -R $latest |
        $zfs receive -vF -d ${local_pool}/${remote_fs%/*}
  fi
fi

# Remove tmp files
#rm -f $local_list $remote_list