#!/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
#  - read the script and adjust to your needs
#  - As root run `borg init -v --encryption=keyfile backup:borg-$HOSTNAME`
#    (note that zsh uses $HOST instead of $HOSTNAME)
#  - If you want, increase the max_segment_size in
#    ssh://backup/borg-$HOSTNAME/config from the default 5MiB

set -e

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

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

	# 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
	/mnt/levant/nfs
	/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_borg <<EOF || true
sh:/home/flo/tmp/*
sh:/home/*/.cache/*
sh:/root/.cache/*
sh:/var/cache/pacman/pkg/*
EOF

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

	# 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"

	# TODO: create snapshots here if possible. Sadly that's really difficult so
	# it will probably not be implemented

	local backupdir="borg-$HOSTNAME"
	backup_borg / "backup:$backupdir"
	ssh backup "touch $backupdir/last-backup-timestamp"
}

backup_borg() {
	local src=$1
	local dst=$2
	local -a options=(
		--verbose
		--numeric-owner
		--compression lz4
		--stats
		--exclude-from "$TMPDIR/exclude-list-borg"
		)

	if tty -s; then
		options+=(--progress)
	fi

	borg create "${options[@]}" "$dst::backup-$(date "+%Y%m%d-%H%M%S")" "$src"
	borg prune --keep-within 7d --keep-daily 7 --keep-weekly 12 --keep-monthly 12 --keep-yearly 3 -v "$dst"
}

### support functions below ###

##
#  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 "${excludeMountpoints[@]}"; do
		excludeList_borg+="sh:$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 "$@"