#!/bin/bash -ue

# The udev rule is not terribly accurate and may trigger our service before
# the kernel has finished probing partitions. Sleep for a bit to ensure
# the kernel is done.
#
# This can be avoided by using a more precise udev rule, e.g. matching
# a specific hardware path and partition.
sleep 5

#
# Script configuration
#

# The backup partition is mounted there
MOUNTPOINT=/mnt

# This is the location of the Borg repository
TARGET=$MOUNTPOINT/Combava

# Archive name schema
DATE=$(date --iso-8601)-$(hostname)

# This is the file that will later contain UUIDs of registered backup drives
DISKS=/etc/backups/backup.disks

# Find whether the connected block device is a backup drive
for uuid in $(lsblk --noheadings --list --output uuid)
do
    if grep --quiet --fixed-strings $uuid $DISKS; then
        break
    fi
    uuid=
done

if [ ! $uuid ]; then
    echo "No backup disk found, exiting"
    exit 0
fi

echo "Disk $uuid is a backup disk"
partition_path=/dev/disk/by-uuid/$uuid
# Mount file system if not already done. This assumes that if something is already
# mounted at $MOUNTPOINT, it is the backup drive. It won't find the drive if
# it was mounted somewhere else.
(mount | grep $MOUNTPOINT) || mount $partition_path $MOUNTPOINT
drive=$(lsblk --inverse --noheadings --list --paths --output name $partition_path | head --lines 1)
echo "Drive path: $drive"

#
# Create backups
#

# Options for borg create
BORG_OPTS="--stats --one-file-system --compression lz4 --checkpoint-interval 86400"

# Set BORG_PASSPHRASE or BORG_PASSCOMMAND somewhere around here, using export,
# if encryption is used.
export BORG_PASSPHRASE="`cat /etc/backups/passphrase`"

# No one can answer if Borg asks these questions, it is better to just fail quickly
# instead of hanging.
export BORG_RELOCATED_REPO_ACCESS_IS_OK=no
export BORG_UNKNOWN_UNENCRYPTED_REPO_ACCESS_IS_OK=no

# Log Borg version
borg --version

echo "Starting backup for $DATE"

# This is just an example, change it however you see fit
borg create $BORG_OPTS \
    --exclude /media/documents/games/ \
    --exclude /media/documents/musique/ \
    --exclude /media/documents/photos/ \
    $TARGET::$DATE-$$-documents \
    /media/documents/

# /home is often a separate partition / file system.
# Even if it isn't (add --exclude /home above), it probably makes sense
# to have /home in a separate archive.
borg create $BORG_OPTS \
    --exclude 'sh:/home/*/.cache' \
    $TARGET::$DATE-$$-home \
    /home/lafrite

echo "Completed backup for $DATE"

# Just to be completely paranoid
sync

if [ -f /etc/backups/autoeject ]; then
    umount $MOUNTPOINT
    hdparm -Y $drive
fi

if [ -f /etc/backups/backup-suspend ]; then
    systemctl suspend
fi