#!/bin/sh
# vim: set sw=4 ts=4 sts=4 et :

check_system() {
    rc=0
    if ! mountpoint -q /boot; then
        echo 'ERROR: /boot is not mounted' >&2
        rc=1
    elif [ ! -w /boot ]; then
        echo 'ERROR: /boot is not writable' >&2
        rc=1
    fi
    if ! mountpoint -q /boot/efi; then
        echo 'ERROR: /boot/efi is not mounted' >&2
        rc=1
    elif [ ! -w /boot/efi ]; then
        echo 'ERROR: /boot/efi is not writable' >&2
        rc=1
    fi
    return ${rc}
}

die() {
    rc=$?
    echo "$1" >&2
    exit ${rc}
}

do_update() {
    if [ -d /boot/efi/.old ]; then
        rm -rf /boot/efi/.old || die 'Failed to remove /boot/efi/.old'
    fi
    mkdir /boot/efi/.old || die 'Failed to create /boot/efi/.old'
    for x in /boot/efi/*; do
        mv "${x}" /boot/efi/.old/ \
            || die "Failed to move ${x} to /boot/efi/.old/"
    done
    mv /boot/rootfs.squashfs /boot/rootfs.squashfs.old \
        || die 'Failed to rename rootfs.squashfs'
    echo 'Extracting root filesystem ...'
    tar -xf "${filename}" -C /boot rootfs.squashfs \
        || die 'Failed to extract rootfs.squashfs'
    echo 'Extracting kernel/initramfs/firmware ...'
    tar -xf "${filename}" -C /boot/efi \
        --exclude rootfs.squashfs \
        --no-same-owner \
        || die 'Failed to extract kernel/initramfs/firmware'
    echo 'The machine will need to be rebooted to complete the update process'
}

usage() {
    printf 'usage: %s filename\n' "${0##*/}"
}

filename=

while [ $# -ge 1 ]; do
    case "$1" in
        -h|--help)
            usage
            exit 0
            ;;
        *)
            filename="$1"
            shift
            ;;
    esac
done

if [ -z "${filename}" ]; then
    usage >&2
    exit 2
fi

check_system || exit $?
do_update