#!/bin/bash
#
# This is a simple backup script using borg. It's supposed to serve as a
# starting point and to be adjusted to your system.
#
# Important steps:
#  - define a host "backup" in root's .ssh/config
#  - You can override variables from main() as well as the pre_backup() and post_backup() functions in
#    $XDG_CONFIG_HOME/backup-sh-conf.sh or /etc/backup-sh-conf.sh
#  - As root run `borg init -v --encryption=keyfile backup:borg-$(hostname)`
#  - If you want, increase the max_segment_size in
#    ssh://backup/borg-$HOSTNAME/config from the default 5MiB
#
# Copyright ©2014-2019 Florian Pritz <bluewind@xinu.at>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
# See gpl-3.0.txt for full license text.

set -eu

main() {
	if [[ $UID != 0 ]]; then
		exec sudo "$0" "$@"
	fi

	TMPDIR="$(mktemp -d "/tmp/${0##*/}.XXXXXX")"
	trap "rm -rf '${TMPDIR}'" EXIT TERM

	# The backup repository used by borg
	borg_repo="backup:borg-$HOSTNAME"

	# These mountpoints will be excluded. Mountpoints not listed in either this
	# or the includeMountpoints variable below will throw an error
	excludeMountpoints=(
		/tmp
		/sys
		/dev
		/proc
		/run
		/media
	)

	# These mountpoints will be included
	includeMountpoints=(
		/
		/boot
		/home
		/mnt/data
	)

	# List of patterns that should be excluded. This supports shell globbing as
	# well as regex pattern. Refer to man borg for details.
	IFS='' read -r -d '' excludeList <<-EOF || true
		sh:/home/*/.cache/*
		sh:/root/.cache/*
		sh:/var/cache/pacman/pkg/*
	EOF

	for configfile in "${XDG_CONFIG_HOME:-$HOME/.config}/backup-sh-conf.sh" /etc/backup-sh-conf.sh; do
		if [[ -e "$configfile" ]]; then
			source "$configfile"
		fi
	done

	exclude_mountpoints
	echo "$excludeList" > "$TMPDIR/exclude-list-borg"

	source_paths=(/)
	backup_prefix="backup"

	if [[ $# -gt 0 ]]; then
		source_paths=()
		backup_prefix="partial"
		for path in "$@"; do
			source_paths+=("$(realpath "$path")")
		done
	fi

	run_if_exists pre_backup
	backup_borg "$backup_prefix" "$borg_repo" "${source_paths[@]}"
	run_if_exists post_backup
}

# This is called before creating the backup
pre_backup() {
	if in_array_startswith '/root/backup-data/' "${source_paths[@]}"; then
		# save some data that's useful for restores
		local backupDataDir=/root/backup-data/
		mkdir -p "$backupDataDir"
		fdisk -l > "$backupDataDir/fdisk"
		vgdisplay > "$backupDataDir/vgdisplay"
		pvdisplay > "$backupDataDir/pvdisplay"
		lvdisplay > "$backupDataDir/lvdisplay"
		df -a > "$backupDataDir/df"
		findmnt -l > "$backupDataDir/findmnt"
		mdadm --detail --scan > "$backupDataDir/mdadm"
		vgcfgbackup --file "$backupDataDir/vgcfgbackup"
	fi

	# If you wish to use snapshots, create them here

	return
}

# This is called after backup creation
post_backup() {
	# If you need to perform any cleanup do so here

	return
}

backup_borg() {
	local backup_prefix=$1; shift
	local dst=$1; shift
	local src=("$@")
	local -a options=(
		--verbose
		--numeric-ids
		--compression lz4
		--exclude-from "$TMPDIR/exclude-list-borg"
		)

	if tty -s; then
		options+=(--progress --stats --list --filter AME)
	fi

	borg create "${options[@]}" "$dst::$backup_prefix-$(date "+%Y%m%d-%H%M%S")" "${src[@]}"

	# Only purge when doing full backups. Increases partial backup speed and
	# ensure that we have at least one recent full backup when we purge.
	if [[ $backup_prefix == 'backup' ]]; then
		borg prune --prefix "backup-" --keep-within 7d --keep-daily 7 --keep-weekly 12 --keep-monthly 6 --keep-yearly 0 -v "$dst"
		borg prune --prefix "partial-" --keep-within 31d -v "$dst"
	fi
}

### support functions below ###

run_if_exists() {
	if declare -F $1 &> /dev/null; then
		$1 "${@:2}"
	fi
}

##
#  usage : in_array( $needle, $haystack )
# return : 0 - found
#          1 - not found
##
in_array() {
    local needle=$1; shift
    local item
    for item in "$@"; do
        [[ $item = "$needle" ]] && return 0 # Found
    done
    return 1 # Not Found
}

# same as in_array except 0 is returned if any item in haystack starts with needle
in_array_startswith() {
    local needle=$1; shift
    local item
    for item in "$@"; do
        [[ "$needle" == "$item"* ]] && return 0 # Found
    done
    return 1 # Not Found
}

exclude_mountpoints() {
	local error=0

	for fs in "${excludeMountpoints[@]}"; do
		excludeList+="sh:$fs/*"$'\n'
	done

	while read line; do
		local mountpoint=$(echo "$line" | cut -d\  -f2 | sed 's#\040# #g;')

		if ! in_array "$mountpoint" "${includeMountpoints[@]}"; then
			if ! in_array_startswith "$mountpoint/" "${excludeMountpoints[@]/%//}"; then
				error=1
				echo "Warning: mountpoint not excluded or included: $mountpoint" >&2
			fi
		fi
	done </etc/mtab

	if ((error)); then
		exit 1
	fi
}

main "$@"