#!/usr/bin/env bash

#
# zfs-backup.sh
#
# Simple backup script utilizing rsync and ZFS snapshots.
#
# rsync must be installed both on the server and the client.
# ssh must be installed on the client.
# bash must be installed on the server.
# The server must use zfs and provide a dataset for each client.
#
# David Prandzioch <kontakt@davidprandzioch.de>
#
# Pass the following environment variables to the script:
#
# * BACKUP_DATASET  : ZFS dataset to use
# * BACKUP_SSH_PATH : Original data SSH path (user@host:path)
# * BACKUP_SSH_PORT : SSH source port (22)
#

DAY_OF_WEEKLY_BACKUP=1      # monday
DAY_OF_MONTHLY_BACKUP="01"  # first day in month


######### DO NOT CHANGE ANYTHING DOWN HERE #########


if [ -z $BACKUP_DATASET ]
then
    echo "Environment variable BACKUP_DATASET not set, exiting"
    exit 1
fi

if [ -z $BACKUP_SSH_PATH ]
then
    echo "Environment variable BACKUP_SSH_PATH not set, exiting"
    exit 1
fi

if [ -z $BACKUP_SSH_PORT ]
then
    echo "Environment variable BACKUP_SSH_PORT not set, exiting"
    exit 1
fi

function delete_snapshots() {
    DATASET=$1
    TYPE=$2

    SNAPSHOTS=$(zfs list -t snapshot -o name | grep "${DATASET}@${TYPE}-")

    for SNAPSHOT in $SNAPSHOTS
    do
        zfs destroy $SNAPSHOT
    done
}

function sync_data() {
    DATASET=$1
    BACKUP_SSH_PATH=$2
    BACKUP_SSH_PORT=$3

    MOUNTPOINT=$(zfs list -o mountpoint $DATASET | grep -v MOUNTPOINT)
    cd $MOUNTPOINT
    rsync -av --progress --delete --inplace -e "ssh -p ${BACKUP_SSH_PORT}" ${BACKUP_SSH_PATH}* .
}

function create_snapshot() {
    DATASET=$1
    TYPE=$2

    zfs snapshot ${DATASET}@${TYPE}-$(date +%Y-%m-%d)
}

sync_data $BACKUP_DATASET $BACKUP_SSH_PATH $BACKUP_SSH_PORT

if [ "$(date +%d)" == "$DAY_OF_MONTHLY_BACKUP" ]
then
    create_snapshot $BACKUP_DATASET "monthly"
    delete_snapshots $BACKUP_DATASET "weekly"
    delete_snapshots $BACKUP_DATASET "daily"
elif [ "$(date +%u)" == "$DAY_OF_WEEKLY_BACKUP" ]
then
    create_snapshot $BACKUP_DATASET "weekly"
    delete_snapshots $BACKUP_DATASET "daily"
else
    create_snapshot $BACKUP_DATASET "daily"
fi

echo "Available snapshots for "$BACKUP_DATASET": "
zfs list -t snapshot -o name | grep "${BACKUP_DATASET}@"