#!/usr/bin/env bash

set -euxo pipefail

# Parse arguments
function help {
    echo "Usage: $0 [-h|-i] volume"
    echo "Backup BTRFS subvolume on rapido to razmo."
    echo
    echo "Arguments:"
    echo "  volume: Name of the subvolume to backup"
    echo
    echo "Options:"
    echo "  -h: Display this help message."
    echo "  -i: Don't fail if the receiving subvolume doesn't exist."
}

init=false
while getopts "hi" OPTION
do
    case "$OPTION" in
        h)
            help
            exit 0
            ;;
        i)
            init=true
            ;;
        ?)
            help
            exit 2
            ;;
    esac
done
shift "$((OPTIND - 1))"

if [ "$#" -ne 1 ]
then
    help
    exit 2
fi
volume="$1"

# Assertions
[ -d "/mnt/rapido/${volume}" ]
[ -d "/mnt/rapido/${volume}.bkp" ] || "$init"
[ ! -d "/mnt/rapido/${volume}.new" ]
[ -d "/mnt/razmo/${volume}.bkp" ] || "$init"
[ -d "/mnt/razmo/${volume}" ] || "$init"
[ ! -d "/mnt/razmo/${volume}.new" ]
[ ! -d "/mnt/razmo/${volume}.snapshots" ]

# Taking a snapshot of the running subvolume
btrfs subvolume snapshot -r "/mnt/rapido/${volume}" "/mnt/rapido/${volume}.new"

# Sending (the difference with) the last backup to the backup disk
function error_handler() {
    btrfs subvolume delete "/mnt/rapido/${volume}.new" || true
    btrfs subvolume delete "/mnt/razmo/${volume}.new" || true
}
trap error_handler ERR
if [ -d "/mnt/rapido/${volume}.bkp" ]
then
    btrfs send -p "/mnt/rapido/${volume}.bkp" "/mnt/rapido/${volume}.new" | btrfs receive /mnt/razmo
else
    btrfs send "/mnt/rapido/${volume}.new" | btrfs receive /mnt/razmo
fi
trap - ERR

# Removing old backups and putting the new one in place
[ ! -d "/mnt/rapido/${volume}.bkp" ] || btrfs subvolume delete "/mnt/rapido/${volume}.bkp"
mv "/mnt/rapido/${volume}.new" "/mnt/rapido/${volume}.bkp"
[ ! -d "/mnt/razmo/${volume}.bkp" ] || btrfs subvolume delete "/mnt/razmo/${volume}.bkp"
mv "/mnt/razmo/${volume}.new" "/mnt/razmo/${volume}.bkp"

# Create a writeable clone in case we need to boot on the HDD
# Needs to move away then back the .snapshots folder
[ ! -d "/mnt/razmo/${volume}/.snapshots" ] || mv "/mnt/razmo/${volume}/.snapshots" "/mnt/razmo/${volume}.snapshots"
[ ! -d "/mnt/razmo/${volume}" ] || btrfs subvolume delete "/mnt/razmo/${volume}"
btrfs subvolume snapshot "/mnt/razmo/${volume}.bkp" "/mnt/razmo/${volume}"
[ ! -d "/mnt/razmo/${volume}.snapshots" ] || mv "/mnt/razmo/${volume}.snapshots" "/mnt/razmo/${volume}/.snapshots"

sync