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

[[ $# -ge 1 && $# -le 3 ]] || {
  echo "usage: render-native-recovery-beacon.sh <output-directory> [beacon-lba] [hosted-entry-id]" >&2
  exit 64
}

mkdir -p "$1"
output_root=$(cd "$1" && pwd)
beacon_lba=${2:-68}
hosted_entry_id=${3:-gnulinux-simple-9842d3d6-a839-4127-bda7-f19137effe71}
[[ ${beacon_lba} =~ ^[0-9]+$ ]]
[[ ${hosted_entry_id} =~ ^[A-Za-z0-9._-]+$ ]]

python3 - "${output_root}" <<'PY'
import pathlib
import sys

output = pathlib.Path(sys.argv[1])
header = (
    b"# GRUB Environment Block\n"
    b"# WARNING: Do not edit this file by tools other than grub-editenv!!!\n"
)

def write_environment(name: str, variables: bytes = b"") -> None:
    prefix = header + variables
    if len(prefix) > 1024:
        raise SystemExit(f"{name} exceeds the GRUB environment-block size")
    (output / name).write_bytes(prefix + b"#" * (1024 - len(prefix)))

write_environment(
    "guanghu-recovery-active.env",
    b"guanghu_recovery=ubuntu\n",
)
write_environment("guanghu-recovery-clear.env")
PY

install -m 0755 /dev/stdin "${output_root}/08_guanghu_native_recovery" <<EOF
#!/bin/sh
exec tail -n +3 \$0
insmod loadenv
set guanghu_recovery=
if load_env --file '(hd0)${beacon_lba}+2' guanghu_recovery; then
    if [ "\${guanghu_recovery}" = "ubuntu" ]; then
        set default="${hosted_entry_id}"
    fi
fi
EOF

sha256sum \
  "${output_root}/guanghu-recovery-active.env" \
  "${output_root}/guanghu-recovery-clear.env" \
  "${output_root}/08_guanghu_native_recovery" \
  >"${output_root}/SHA256SUMS"