#!/usr/bin/env bash
set -euo pipefail

DEVICE=$(readlink -f -- "${DEVICE}")
REGEXP='^/dev/n?st([0-9]+)[alm]?$'

if [[ ! $DEVICE =~ $REGEXP ]]; then
    echo "'$DEVICE' doesn't match" >&2
    exit 1
fi

NUM="${BASH_REMATCH[1]}"
# sg_map opens devices and omits the Tape mapping while LTFS holds the SG device.
# The kernel mapping remains available throughout mount and unmount.
DEVICE_PATH=$(readlink -f -- "/sys/class/scsi_tape/st${NUM}/device")
shopt -s nullglob
SG_DEVICES=("${DEVICE_PATH}"/scsi_generic/sg*)
if [[ ${#SG_DEVICES[@]} -ne 1 || ! -d ${SG_DEVICES[0]} ]]; then
    echo "'$DEVICE' has no unique SCSI generic device" >&2
    exit 1
fi
printf '/dev/%s\n' "${SG_DEVICES[0]##*/}"