#!/bin/bash

set -eu

function snap {
    unsnap

    znap-take bsnap 1
    mount_snapshots
    mkdir -p /a/boot
    mount --bind /boot /a/boot
}

function unsnap {
    if ! [ -d /a ]; then
        return
    fi

    umount /a/boot || true
    rmdir /a/boot || true

    if ls &> /dev/null /a/*; then
        umount /a/* || true
        rmdir /a/* || true
    fi
    rmdir /a || true
}

function list_snapshots {
    local fsname
    for fsname in $(zfs list -H -o name); do
        zfs list -H -o name -S creation -t snapshot -d 1 -r "$fsname" | \
            grep '@znap_....-..-..-...._bsnap' | \
            head -n1
    done
}

function mount_snapshots {
    local snapname
    local fsname
    local mountpoint

    for snapname in $(list_snapshots); do
        fsname="${snapname%@*}"
        mountpoint="/a/$(echo "$fsname" | cut -d/ -f2- | tr '/' '_')"
        mkdir -p "$mountpoint"
        mount -t zfs "$snapname" "$mountpoint"
    done
}

if [ "$(id -u)" -ne 0 ]; then
    echo "Must be root"
    exit 1
fi

if [ "${1:-}" = "off" ]; then
    unsnap
elif [ "${1:-}" = "on" ]; then
    snap
else
    echo "Usage: $0 on|off"
    exit 1
fi