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

[[ $# -ge 2 && $# -le 3 ]] || {
  echo "usage: clear-native-recovery-beacon.sh <disk> <clear-template> [beacon-lba]" >&2
  exit 64
}

disk=$1
clear_template=$2
beacon_lba=${3:-68}
[[ ${beacon_lba} =~ ^[0-9]+$ ]]
[[ -f ${clear_template} ]]
[[ $(stat -c %s "${clear_template}" 2>/dev/null || stat -f %z "${clear_template}") -eq 1024 ]]

if [[ -b ${disk} ]]; then
  [[ ${EUID} -eq 0 ]]
  [[ $(readlink -f "${disk}") == /dev/vda ]]
elif [[ ! -f ${disk} ]]; then
  echo "recovery beacon target is neither /dev/vda nor a test disk" >&2
  exit 65
fi

readback=$(mktemp)
trap 'rm -f "${readback}"' EXIT
dd if="${disk}" of="${readback}" bs=512 skip="${beacon_lba}" count=2 status=none

if cmp -s "${readback}" "${clear_template}"; then
  echo "GUANGHU_NATIVE_RECOVERY_BEACON_ALREADY_CLEAR"
  exit 0
fi

if ! grep -aFq 'guanghu_recovery=ubuntu' "${readback}"; then
  echo "unknown data occupies the recovery beacon sectors" >&2
  exit 65
fi

dd if="${clear_template}" of="${disk}" bs=512 seek="${beacon_lba}" count=2 \
  conv=notrunc,fsync status=none
dd if="${disk}" of="${readback}" bs=512 skip="${beacon_lba}" count=2 status=none
cmp "${readback}" "${clear_template}"
echo "GUANGHU_NATIVE_RECOVERY_BEACON_CLEARED"