#!/bin/bash
#
# Incremental replication of ALL Incus instances (incus copy --refresh;
# with ZFS on both ends only deltas travel, so stopped instances cost
# nothing after their first copy).
# https://linuxcontainers.org/incus/docs/main/howto/move_instances/
#
# Three shapes, per where it runs and where the replicas land:
#   incus-copy.sh -d <dest-remote> [-m pull|push|relay] [-s <dest-pool>]
#       push all local instances to a remote (runs on the source host)
#   incus-copy.sh -r <src-remote> [-m pull|push|relay] [-s <dest-pool>]
#       pull all of a remote's instances to the local host (runs on the
#       backup host; the source only needs its API reachable)
#   incus-copy.sh -p <target-project> -s <dest-pool>
#       copy all local instances into another local project + pool
#       (on-host backup onto a different disk)
#
# Snapshot history/retention is handled on the source instances
# (snapshots.schedule / snapshots.expiry); --refresh-exclude-older keeps
# refreshes from dragging expired snapshots around.

set -u

INCUS=/usr/bin/incus
LOCKFILE=/run/lock/incus-copy.lock
SRC=""
DEST=""
MODE=pull
POOL=""
PROJECT=""

usage() {
    echo "Usage: $0 [-d <dest-remote> | -r <src-remote>] [-m pull|push|relay] [-s <dest-storage-pool>] [-p <dest-project>]" >&2
    exit 2
}

while getopts d:r:m:s:p: flag; do
    case "${flag}" in
        d) DEST=${OPTARG};;
        r) SRC=${OPTARG};;
        m) MODE=${OPTARG};;
        s) POOL=${OPTARG};;
        p) PROJECT=${OPTARG};;
        *) usage;;
    esac
done
# need somewhere for replicas to go, and one side must stay local
[ -n "$DEST" ] || [ -n "$SRC" ] || [ -n "$PROJECT" ] || usage
[ -n "$DEST" ] && [ -n "$SRC" ] && usage
case "$MODE" in pull|push|relay) ;; *) usage;; esac

# refuse to overlap with a previous, still-running invocation
exec 9> "$LOCKFILE"
if ! flock -n 9; then
    echo "another incus-copy run holds $LOCKFILE, aborting" >&2
    exit 1
fi

INSTANCES=$($INCUS list ${SRC:+"${SRC}:"} -c n -f csv) || {
    echo "cannot list instances${SRC:+ on ${SRC}:}, aborting" >&2
    exit 1
}

RC=0
for CT in $INSTANCES; do
    echo "[$(date '+%F %T')] copy ${SRC:+$SRC:}$CT -> ${DEST:+$DEST:}$CT${PROJECT:+ (project $PROJECT)}"
    # --mode only applies to remote transfers; --quiet suppresses the
    # \r-progress meter that turns log files into mangled one-liners
    if $INCUS copy --quiet "${SRC:+$SRC:}$CT" "${DEST:+$DEST:}$CT" \
        --refresh --refresh-exclude-older \
        ${SRC:+--mode "$MODE"} ${DEST:+--mode "$MODE"} \
        ${POOL:+--storage "$POOL"} \
        ${PROJECT:+--target-project "$PROJECT"}; then
        # the replica inherits boot.autostart from the source and would
        # start itself on the backup host after a reboot (or, for the
        # local-project shape, fight the live instance for its static
        # IP on the same bridge) — neutralize it
        $INCUS config set ${PROJECT:+--project "$PROJECT"} \
            "${DEST:+$DEST:}$CT" boot.autostart=false || RC=1
    else
        echo "[$(date '+%F %T')] FAILED: $CT" >&2
        RC=1
    fi
done

exit $RC