#!/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.

set -e

declare -r description="latest incremental backup"

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

# It's important not to change this userdata in the snapshots, since that's how
# we find the previous one.

TARGETS="$(findmnt -n -v -t btrfs -o TARGET --list)"
UUIDS="$(findmnt -n -v -t btrfs -o UUID --list)"

declare -a TARGETS_ARRAY
declare -a UUIDS_ARRAY

i=0
for x in $TARGETS; do
    TARGETS_ARRAY[$i]=$x
    i=$((i+1))
done
i=0
for x in $UUIDS; do
    UUIDS_ARRAY[$i]=$x
    i=$((i+1))
done
printf "Select a mounted BTRFS device to backup to.\n"
disk=-1
while [[ $disk -lt 0 || $disk -gt $i ]]; do
    for x in "${!TARGETS_ARRAY[@]}"; do
        printf "%s) %s (%s)\n" "$((x+1))" "${UUIDS_ARRAY[$x]}" "${TARGETS_ARRAY[$x]}"
    done
    printf "0) Exit\n"
    read -r -p "Enter a number: " disk
done
if [[ $disk == 0 ]]; then
    exit 0
fi
selected_uuid="${UUIDS_ARRAY[$((disk-1))]}"
selected_mnt="${TARGETS_ARRAY[$((disk-1))]}"
printf "You selected the disk with UUID %s.\n" "$selected_uuid"

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

for x in $SNAPPER_CONFIGS; do

    source /etc/snapper/configs/$x

    printf "At '%s' configuration\n" "$x"

    old_number=$(snapper -c "$x" list -t single | awk '/'"$selected_uuid"'/ {print $1}')
    old_snapshot=$SUBVOLUME/.snapshots/$old_number/snapshot

    if [[ -z "$old_number" ]]; then
        printf "No backups have been performed for '%s' on this disk.\n" "$x"
        read -r -p "Enter name of directory to store backups, relative to $selected_mnt (to be created if not existing): " mybackupdir
        printf "This will be the initial backup for snapper configuration '%s' to this disk. This could take awhile.\n" "$x"
        BACKUPDIR="$selected_mnt/$mybackupdir"
        mkdir -p "$BACKUPDIR"
    else
        mybackupdir=$(snapper -c root list -t single | awk -F"|" '/'"$selected_uuid"'/ {print $5}' | awk -F "," '{print $1}' | awk -F"=" '{print $2}')
        BACKUPDIR="$selected_mnt/$mybackupdir"
        if [[ ! -d $BACKUPDIR ]]; then
            printf "ERROR: %s is not a directory on %s.\n" "$BACKUPDIR" "$selected_uuid"
            exit 1
        fi
    fi

    new_number=$(snapper -c "$x" create --print-number)
    new_snapshot=$SUBVOLUME/.snapshots/$new_number/snapshot
    new_info=$SUBVOLUME/.snapshots/$new_number/info.xml
    sync
    backup_location=$BACKUPDIR/$x/$new_number/
    printf "Backup location: %s\n" "$backup_location"

    read -r -p "Continue [Y/n]? " cont_backup
    printf "\n"
    if [[ "$cont_backup" != [Yy]"es" && "$cont_backup" != [Yy] ]]; then
        printf "Skipping this configuration.\n"
        continue
    fi

    mkdir -p "$backup_location"


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

        btrfs send "$new_snapshot" | btrfs receive "$backup_location" &>/dev/null

    else

        # 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 "$backup_location" &>/dev/null
        cp "$new_info" "$backup_location"
        snapper -c "$x" delete "$old_number"
    fi

    userdata="backupdir=$mybackupdir, uuid=$selected_uuid"

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

done

printf "Done!\n"