#!/bin/bash
# Create archived backups of zfs datasets, with support for incremental backups from automated snapshots.
# Usage: backup-zfs-dataset [OPTIONS] <dataset> <destination>

usage() {
    >&2 printf "Usage: %s [OPTIONS] [<dataset> <destination>]\n" "$0"
    >&2 printf "Options:\n"
    >&2 printf "\t-c  --compression-level <level>       \t Specify compression level (integer)\n"
    >&2 printf "\t-s  --dataset <dataset name>          \t Specify dataset name\n"
    >&2 printf "\t-d  --destination <path to directory> \t Specify destination\n"
    >&2 printf "\t-m  --max-size <size>                 \t Specify maximum size of archive parts\n"
    >&2 printf "\t-f  --force                           \t Force overwriting existing backups if the backup already exists\n"
    exit "${1:-1}"
}

# Get options.

while [[ $# -gt 0 ]]; do
    case "${1}" in
        -c | --compression_level)
            if ! [[ "${2}" =~ [[:digit:]] ]]; then
                >&2 printf "Error: Invalid compression level: '%s'\n" "${2}"
                usage
            fi
            compression_level="${2}"
            shift 2
            ;;
        -s | --dataset)
            if ! [ -n "${2}" ]; then
                >&2 printf "Error: Invalid dataset: '%s'\n" "${2}"
                usage
            fi
            dataset="${2}"
            shift 2
            ;;
        -d | --destination)
            if ! [ -d "${2}" ]; then
                >&2 printf "Error: Specified destination does not exist: '%s'\n" "${2}"
                usage
            fi
            destination="${2}"
            shift 2
            ;;
        -m | --max-size)
            if ! [[ "${2}" =~ [[:digit:]](K|M|G) ]]; then
                >&2 printf "Error: Invalid maximum size: '%s'\n" "${2}"
                usage
            fi
            max_size="${2}"
            shift 2
            ;;
        -f | --force)
            force_create_manual_backup=1
            shift 1
            ;;
        *)
            >&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
elif ! [ -d "${destination}" ]; then
    >&2 printf "Error: Specified destination does not exist: '%s'\n" "${2}"
    usage
fi

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

# Working snapshots

# Find snapshots
snapshot_location="/mnt/${dataset}/.zfs/snapshot"
latest_auto="$( find "${snapshot_location}"/* -maxdepth 0 -name 'auto*' -type d | sort -n | tail -n1 | xargs -n1 basename )"
latest_manual="$( find "${snapshot_location}"/* -maxdepth 0 -name 'manual*' -type d | sort -n | tail -n1 | xargs -n1 basename )"

# Check snapshots existance
if ! [ -n "${latest_manual}" ]; then
    >&2 printf "Error: No manual snapshot could be found!\n"
    exit 2
fi
if ! [ -n "${latest_auto}" ]; then
    >&2 printf "Error: No automatic snapshot could be found!\n"
    exit 2
fi

printf "Latest manual snapshot: %s\nLatest auto snapshot: %s\n" "${latest_manual}" "${latest_auto}"

# Abort entire script if anything fails.
set -e

# Backups

# Base backup.
output_filename="${destination}/${latest_manual}.gz"
existing_backup="$( find "${destination}" -type f -name "${latest_manual}.gz.part.[a-z][a-z]" -print -quit )"
if [ -z ${existing_backup} ]; then
    printf "Info: If you've manually created a new snapshot, you might want to remove the old backups.\n"
    printf "Latest manual snapshot was not yet backed up, backing up now.\n"
    sudo zfs send --verbose "${dataset}@${latest_manual}" \
        | gzip "-${compression_level}" --verbose --rsyncable \
        | split - --verbose -b "${max_size}" "${output_filename}.part."
    printf "Written manual backup to: %s\n" "${output_filename}"
elif [ "${force_create_manual_backup}" ]; then
    printf "Removing previous backup files.\n"
    find "${destination}" -type f -name "${latest_manual}.gz.part.[a-z][a-z]" -print -delete
    printf "Backing up manual snapshot.\n"
    sudo zfs send --verbose "${dataset}@${latest_manual}" \
        | gzip "-${compression_level}" --verbose --rsyncable \
        | split - --verbose -b "${max_size}" "${output_filename}.part."
    printf "Written manual backup to: %s\n" "${output_filename}"
else
    printf "Found existing backup of manual snapshot: %s\n" "${existing_backup}"
fi

# Incremental incremental backup.
printf "Creating incremental backup between %s and %s\n" "${latest_manual}" "${latest_auto}"
output_filename="${destination}/${latest_manual}-${latest_auto}.gz"
sudo zfs send --verbose -i "@${latest_manual}" "${dataset}@${latest_auto}" \
    | gzip "-${compression_level}" --verbose \
    | split - --verbose -b "${max_size}" "${output_filename}.part."
printf "Written incremental backup to: %s\n" "${output_filename}"

# TODO Cleanup

printf "Done!\n"