#!/bin/bash
# Create archived backups of zfs datasets
# Usage: backup-zfs-dataset [OPTIONS] [<dataset> <destination>]

# This script makes use of SFTP and authenticates using the .netrc file in the users home directory.
# You should configure your system accordingly.

usage() {
    >&2 printf "Usage: %s [OPTIONS] [<dataset> <destination>]\n" "$0"
    >&2 printf "Options:\n"
    >&2 printf "\t-s  --dataset <dataset name>          \t Specify dataset name\n"
    >&2 printf "\t-d  --destination <path to directory> \t Specify destination\n"
    >&2 printf "\t-b  --base                            \t Create a new base\n"
    >&2 printf "\t-i  --incremental                     \t (Default) Create a new incremental backup\n"
    >&2 printf "\t-c  --compression-level <level>       \t Specify compression level (integer)\n"
    >&2 printf "\t-m  --max-size <size>                 \t Specify maximum size of archive parts\n"
    >&2 printf "\t-t  --tag <tag>                       \t Provide a name to tag the archive\n"
    exit "${1:-1}"
}

# Get options.

while [[ $# -gt 0 ]]; do
    case "${1}" in
        -s | --dataset)
            if ! [ -n "${2}" ]; then
                >&2 printf "Error: Invalid dataset: '%s'\n" "${2}"
                usage
            fi
            dataset="${2}"
            shift 2
            ;;
        -d | --destination)
            destination="${2}"
            shift 2
            ;;
	-b | --base)
	    if [ "${create_base:=1}" -ne 1 ]; then
                >&2 printf "Error: Cannot create base backup when specifying differently.\n"
		usage
	    fi
	    shift 1
	    ;;
        -i | --incremental)
	    if [ "${create_base:=0}" -ne 0 ]; then
	        >&2 printf "Error: Cannot create incremental backup when specifying differently.\n"
		usage
            fi
	    shift 1
	    ;;
        -c | --compression_level)
            if ! [[ "${2}" =~ [[:digit:]] ]]; then
                >&2 printf "Error: Invalid compression level: '%s'\n" "${2}"
                usage
            fi
            compression_level="${2}"
            shift 2
            ;;
        -m | --max-size)
            if ! [[ "${2}" =~ [[:digit:]](K|M|G) ]]; then
                >&2 printf "Error: Invalid maximum size: '%s'\n" "${2}"
                usage
            fi
            max_size="${2}"
            shift 2
            ;;
	-t | --tag)
	    tag="${2}-"
	    shift 2
	    ;;
        *)
            >&2 printf "Error: Invalid option: '%s'\n" "${1}"
            usage
            ;;
    esac
done

# Check arguments.

if [[ -z "${dataset:=${1}}" || -z "${destination:=${2}}" ]]; then
    >&2 printf "Error: You need to specify a dataset and a destination.\n"
    usage
elif [ -z "${dataset}" ]; then
    >&2 printf "Error: Invalid dataset: '%s'\n" "${1}"
    usage
fi

# Set defaults
compression_level="${compression_level:=1}"
max_size="${max_size:=2G}"

# Check if you need to make a new base backup
if [ "${create_base:=0}" -eq 1 ]; then
    snapshot_name="manual-$( date +%Y-%m-%d_%H-%M )"
    output_filename="${destination}/${tag:=}${snapshot_name}.gz"
    # Create ZFS snapshot
    printf "Creating snapshot\n"
    sudo zfs snapshot -r "${dataset}@${snapshot_name}"
    # Compress it
    printf "Backing up now\n"
    sudo zfs send --verbose -R "${dataset}@${snapshot_name}" \
        | gzip "-${compression_level}" --verbose --rsyncable \
        | split - --verbose -b "${max_size}" \
            --filter "curl --netrc -kaT - ftp://${output_filename}"
            # Same as curl --netrc --insecure --append --upload-file
    printf "Written base backup to: '%s'.\n" "${output_filename}"
    printf "Done!\n"
    exit 0
fi

# Working snapshots

# Find snapshots
snapshots="$( find "/mnt/${dataset}/.zfs/snapshot"/* -maxdepth 0 -type d | sed -E 's/.*-([0-9]{4}-[0-9]{2}-[0-9]{2}_[0-9]{2}-[0-9]{2})/\1\t&/' | sort -n | cut -f 2- | xargs -n1 basename )"
# Use the two latest snapshots
from_snapshot="$( tail -n2 <<< "${snapshots}" | head -n1 )"
to_snapshot="$( tail -n2 <<< "${snapshots}" | tail -n1 )"

# Check snapshots existance
if [ -z "${from_snapshot}" ] || [ -z "${to_snapshot}" ]; then
    >&2 printf "Error: Less than two snapshots could be found:\n"
    >&2 printf "       From: '%s'\n" "${from_snapshot}"
    >&2 printf "       To:   '%s'\n" "${to_snapshot}"
    exit 2
fi

# Abort entire script if anything fails.
set -e

# Backups

# Incremental incremental backup.
printf "Creating incremental backup between '%s' and '%s'\n" "${from_snapshot}" "${to_snapshot}"
output_filename="${destination}/${tag}${from_snapshot}-${to_snapshot}.gz"
sudo zfs send --verbose -R -i "@${from_snapshot}" "${dataset}@${to_snapshot}" \
    | gzip "-${compression_level}" --verbose \
    | split - --verbose -b "${max_size}" \
        --filter "curl --netrc -kaT - ftp://${output_filename}"
        # Same as curl --netrc --insecure --append --upload-file
printf "Written incremental backup to: %s\n" "${output_filename}"

# TODO Cleanup

printf "Done!\n"