#!/bin/bash
# James W. Barnett

declare -r mybackupdir="/run/media/wes/backup/acer-c720"

#--------------------------------------------------------
# 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.
declare -r userdata="extbackup=yes"
declare -r configs="$(find /etc/snapper/configs/* -printf '%f\t\0')"

for x in $configs; do

    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
        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/$new_number/
        old_backup=$BACKUPDIR/$x/$old_number/snapshot

        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

            echo "The latest incremental backup snapshot for snapper configuration '$x' "
            echo "is $new_number. Do not delete this snapshot, or you when you run this "
            echo "script again, it will send ALL data again, not just the incremental change. "

        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