#!/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.

version="0.2"

set -e

while [[ $# -gt 0 ]]; do
    key="$1"
    case $key in
        -d|--description)
            description="$2"
            shift 2
        ;;
        -c|--config)
            selected_configs="$2"
            shift 2
        ;;
        -u|--UUID)
            uuid_cmdline="$2"
            shift 2
        ;;
        -n|--noconfirm)
            noconfirm="yes"
            shift
        ;;
        -h|--help)
            printf "snap-sync $version\n\n"
            printf "Usage: snap-sync [options]\n\n"
            printf "Options:\n"
            printf " -d, --description <desc> Change the snapper description. Default: \"latest incremental backup\"\n"
            printf " -c, --config <config>    Specify the snapper configuration to use. Otherwise will perform for each snapper\n"
            printf "                          configuration. Can list multiple configurations within quotes, space-separated\n"
            printf "                          (e.g. -c \"root home\").\n"
            printf " -n, --noconfirm          Do not ask for confirmation for each configuration. Will still prompt for backup\n"
            printf "                          directory name on first backup\n"
            printf " -u, --UUID <UUID>        Specify the UUID of the mounted BTRFS subvolume to back up to. Otherwise will prompt.\n"
            printf "                          If multiple mount points are found with the same UUID, will prompt user.\n"
            exit 1
        ;;
        *)
            printf "ERROR: Unknown option: $key\n"
            printf "Run 'snap-sync -h' for valid options.\n"
            exit 1
        ;;
    esac
done

description=${description:-"latest incremental backup"}
uuid_cmdline=${uuid_cmdline:-"none"}
noconfirm=${noconfirm:-"no"}

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
disk=-1
disk_count=0
for x in $UUIDS; do
    UUIDS_ARRAY[$i]=$x
    if [[ "$x" == "$uuid_cmdline" ]]; then
        disk=$i
        disk_count=$(($disk_count+1))
    fi
    i=$((i+1))
done

i=0
for x in $TARGETS; do
    TARGETS_ARRAY[$i]=$x
    i=$((i+1))
done

if [[ "$disk_count" > 1 ]]; then
    printf "Multiple mount points were found with UUID $uuid_cmdline.\n"
    disk="-1"
fi

if [[ "$disk" == -1 ]]; then
    if [[ "$disk_count" == 0 && "$uuid_cmdline" != "none" ]]; then
        printf "ERROR: A device with UUID $uuid_cmdline was not found to be mounted, or it is not a BTRFS device.\n"
    fi
    printf "Select a mounted BTRFS device to backup to.\n"
    while [[ $disk -lt 0 || $disk -gt $i ]]; do
        for x in "${!TARGETS_ARRAY[@]}"; do
            printf "%4s) %s (%s)\n" "$((x+1))" "${UUIDS_ARRAY[$x]}" "${TARGETS_ARRAY[$x]}"
        done
        printf "%4s) Exit\n" "0"
        read -r -p "Enter a number: " disk
    done
    if [[ $disk == 0 ]]; then
        exit 0
    fi
    disk=$(($disk-1))
fi

selected_uuid="${UUIDS_ARRAY[$((disk))]}"
selected_mnt="${TARGETS_ARRAY[$((disk))]}"
printf "\nYou selected the disk with UUID %s.\n" "$selected_uuid"
printf "The disk is mounted at %s.\n" "$selected_mnt"

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

selected_configs=${selected_configs:-$SNAPPER_CONFIGS}

for x in $selected_configs; do

    printf "\n"

    if [[ -f "/etc/snapper/configs/$x" ]]; then
        source /etc/snapper/configs/$x
    else
        printf "ERROR: Selected snapper configuration $x does not exist.\n"
        exit 1
    fi

    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 -m700 "$BACKUPDIR"
    else
        mybackupdir=$(snapper -c root list -t single | awk -F"|" '/'"$selected_uuid"'/ {print $5}' | awk -F "," '/backupdir/ {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 -d "snap-sync backup in progress")
    new_snapshot=$SUBVOLUME/.snapshots/$new_number/snapshot
    new_info=$SUBVOLUME/.snapshots/$new_number/info.xml
    sync
    backup_location=$BACKUPDIR/$x/$new_number/
    printf "Will backup %s to %s\n" "$new_snapshot" "$backup_location/snapshot"

    if [[ $noconfirm == "yes" ]]; then
        cont_backup="yes"
    else
        read -r -p "Continue with backup [Y/n]? " cont_backup
    fi

    if [[ "$cont_backup" != [Yy]"es" && "$cont_backup" != [Yy] && -n "$cont_backup" ]]; then
        printf "Aborting backup for this configuration.\n"
        snapper -c $x delete $new_number
        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 "$backup_location" &>/dev/null
        snapper -c "$x" delete "$old_number"
    fi

    cp "$new_info" "$backup_location"

    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 "\nDone!\n"