#!/bin/bash

boot_dir='/boot/syslinux'
boot_dir="${boot_dir%/}"
boot_fs="$(findmnt --noheadings --target "${boot_dir}" --output 'SOURCE')" || {
    printf -- '%s\n' \
        'Unable to identify boot drive for '"'${boot_dir}'"' boot dir.' \
        'Cowardly exiting. No syslinux files nor MBR were overwritten.'
    exit 1
}
if [[ "$(<<<"${boot_fs}" wc -l)" -gt '1' ]]; then
    printf -- '%s\n' \
        'More than one drive mounted at '"'${boot_dir}'"' boot dir.' \
        'Cowardly exiting. No syslinux files nor MBR were overwritten.'
    exit 1
fi

boot_disk="$(lsblk --output 'NAME' --json --tree | jq --raw-output '.[][] | select(.children | length > 0) | select(.children[].name=="'"${boot_fs}"'") | .name')"
if [[ ! "${boot_disk}" ]]; then
    # There's no parent drive over "${boot_fs}" meaning "${boot_fs}" itself
    # already is the parent. This is a file system on a drive and not on a
    # partition.
    boot_disk="${boot_fs}"
fi

find "${boot_dir}" -type f -iname '*.c32' -delete
rsync -a '/usr/lib/syslinux/bios/'*'.c32' "${boot_dir}"'/'
extlinux --install "${boot_dir}"
dd bs=440 count=1 conv=notrunc if='/usr/lib/syslinux/bios/mbr.bin' of="${boot_disk}"