#!/bin/bash
# James W. Barnett

# Takes snapshots of each snapper configuration. It then sends the snapshot to
# a location on an external drive. After the initial transfer, it does
# incremental snapshots on later calls. It's important not to delete the
# snapshot created on your system since that will be used to determine the
# difference for the next incremental snapshot.

# Can set the backup directory here, or in the snapper configuration file with
# EXT_BACKUP_LOCATION
declare -r mybackupdir="/run/media/wes/backup/acer-c720"

# You can set a snapper configuration to be excluded by setting EXT_BACKUP="no"
# in its snapper configuration file.

#--------------------------------------------------------
# Don't modify anything below here

set -e

if [[ $EUID -ne 0 ]]; then
    echo "Script must be run as root." 
    exit
fi

declare -r description="latest incremental backup"

# It's important not to change this userdata in the snapshots, since that's how
# we find the previous one.
UUID="$(blkid -L backup | awk -F'/' '{print $4}')"
declare -r userdata="uuid=$UUID"
#declare -r userdata="extbackup=yes"

if [[ -f /etc/conf.d/snapper ]]; then
    source /etc/conf.d/snapper 
else
    echo "ERROR: /etc/conf.d/snapper does not exist!"
    exit 1
fi

for x in $SNAPPER_CONFIGS; do

    # shellcheck source=/dev/null
    source /etc/snapper/configs/$x

    do_backup=${EXT_BACKUP:-"yes"}

    if [[ $do_backup == "yes" ]]; then

        BACKUPDIR=${EXT_BACKUP_LOCATION:-"$mybackupdir"}

        if [[ -z $BACKUPDIR ]]; then
            echo "ERROR: External backup location not set!"
            exit 1
        elif [[ ! -d $BACKUPDIR ]]; then
            echo "ERROR: $BACKUPDIR is not a directory."
            exit 1
        fi

        old_number=$(snapper -c "$x" list -t single | awk '/'"$userdata"'/ {print $1}')
        new_number=$(snapper -c "$x" create --print-number)
        sync
        
        new_snapshot=$SUBVOLUME/.snapshots/$new_number/snapshot
        new_info=$SUBVOLUME/.snapshots/$new_number/info.xml
        backup_location=$BACKUPDIR/$x/$new_number/

        mkdir -p "$backup_location"

        if [[ -z "$old_number" ]]; then

            echo "Performing initial backup for snapper configuration '$x'. This could take awhile..."
            btrfs send "$new_snapshot" | btrfs receive "$backup_location"

        else

            old_snapshot=$SUBVOLUME/.snapshots/$old_number/snapshot

            # Sends the difference between the new snapshot and old snapshot to
            # the backup location. Using the -c flag instead of -p tells it that
            # there is an identical subvolume to the old snapshot at the
            # receiving location where it can get its data. This helps speed up
            # the transfer.
            btrfs send "$new_snapshot" -c "$old_snapshot" | btrfs receive "$backup_location"

            cp "$new_info" "$backup_location"
            snapper -c "$x" delete "$old_number"

        fi

        # Tag new snapshot as the latest
        snapper -v -c "$x" modify -d "$description" -u "$userdata" "$new_number"

    fi

done

date > "$HOME"/.lastbackup