#!/bin/bash
set -e -o pipefail

confdir=/etc/btrfs
blacklist=$confdir/blacklist.txt

with_subvolumes()
{
    btrfs subvolume list / -a |
        while read _ id _ gen _ _ toplevel _ path
        do
            "$@"
        done
}

fixup_path()
{
    if ! [ "$root" ]
    then
        case "$path" in
            '<FS_TREE>'/* ) root=${path#*/} ;;
            * ) exit 1 ;;
        esac
    fi
    case "$path" in
        '<FS_TREE>'/"$root"/* ) path_fixed=${path#*/$root} ;;
        "$root"/* ) path_fixed=${path#$root} ;;
        * ) return ;;
    esac
    "$@"
}

is_our_snapshot()
{
  case "$1" in
    */.snapshot~* ) true ;;
    *) false ;;
  esac
}

filter_readonly()
{
    if btrfs subvolume show -r "$id" / | sed -Ene '/^\tFlags:.*\breadonly\b/q' -e '$q1'
    then
        if [ -e "$conf_name" ]
        then
            printf '%20s %s\n' rm "$conf_name" >&2
            rm "$conf_name"
        fi
        printf '%20s %s\n' '(readonly) lose' "$path_fixed" >&2
        return
    fi
    "$@"
}

filter_snapshot_filename()
{
    if is_our_snapshot "$path_fixed"
    then
        if [ -e "$conf_name" ]
        then
            printf '%20s %s\n' rm "$conf_name" >&2
            rm "$conf_name"
        fi
        printf '%20s %s\n' '(snapshot) lose' "$path_fixed" >&2
        return
    fi
    "$@"
}

systemctl_disable_quiet()
{
    ! systemctl is-enabled "$@" 2>/dev/null || systemctl disable "$@"
}

timer_prefix=/etc/systemd/system/default.target.wants/push-btrfs@borges
unset blacklist_patterns
declare -a blacklist_patterns
filter_blacklist()
{
    if [ "$blacklist" -a -f "$blacklist" ]
    then
        if ! [ -v blacklist_patterns ]
        then
            readarray -t blacklist_patterns < "$blacklist"
        fi

        for pattern in "${blacklist_patterns[@]}"
        do
            if [[ $path_fixed == $pattern ]]
            then
                printf '%20s %s\n' '(blacklist) lose' "$path_fixed" >&2
                if [ -e "$conf_name" ]
                then
                    printf '%20s %s\n' rm "$conf_name" >&2
                    rm "$conf_name"
                fi
                timer=$destination_host$(systemd-escape "$path_fixed").timer
                systemctl_disable_quiet "$timer"
                return
            fi
        done
    fi
    "$@"
}

compute_paths()
{
    source=$path_fixed
    source_escaped=$(systemd-escape "$source")
    conf_dir=/etc/btrfs/remotes
    conf_name="$conf_dir"/$destination_host$source_escaped.json
    "$@"
}

mirror()
{
    if [ -e "$conf_name" ]
    then
        return
    fi
    set -- \
        jq -c -n '{source: $source, destination: $destination}' \
        --arg destination "$destination$source_escaped" \
        --arg source "$source"

    if [ ! "$NO_ACT" ]
    then
        conf_temp=$conf_name~$(date -Ins)
        {
            "$@" > "$conf_temp"
            mv -T -- "$conf_temp" "$conf_name"
            printf '%20s %s\n' 'add' "$path_fixed" >&2
        } || {
            rm -- "$conf_temp"
            false
        }
    fi

    if [ "$ONLY_ONCE" ]
    then
        exit 0
    fi
}

usage()
{
cat <<END
usage: $0 [-n] [-r]
END
}

case "$0" in
    ./* ) PATH=${0%/*}:$PATH ;;
esac

case "$(id -u)" in
          0 ) ;;
          * ) exec sudo --preserve-env=VERBOSE "$0" "$@" || exit ;;
esac

while [ $# -gt 0 ]
do
    case "$1" in
        -- ) shift
             break ;;
        -n ) NO_ACT=y ;;
        -r ) export RESUME=y ;;
        -v ) VERBOSE=y ;;
        --once ) ONLY_ONCE=y ;;
        --destination ) DESTINATION=$2
                        shift ;;
        -* ) usage
             exit 1 ;;
        * ) break ;;
    esac
    shift
done

destination_file=/etc/btrfs/destination.txt
[ "$DESTINATION" ] || read DESTINATION < "$destination_file"

destination_host=${DESTINATION%%:*}
destination_basename=$(hostname) && [ "$destination_basename" ] || destination_basename=btrfs
case "$DESTINATION" in
    */ ) destination=$DESTINATION$destination_basename ;;
    [a-zA-Z]* ) destination=$DESTINATION ;;
    * ) exit 1 ;;
esac

ssh root@"$destination_host" true || read -p 'Could not log in.  Continue? '

with_subvolumes fixup_path \
                compute_paths \
                filter_snapshot_filename \
                filter_readonly \
                filter_blacklist \
                mirror