#!/usr/bin/env bash
# Wrap a built punktfunk-host pacman package into a systemd-sysext image — the update-survivable
# way to add the host to an immutable Arch-derived distro (SteamOS 3): the .raw overlays /usr
# read-only from the writable /var/lib/extensions/, so it persists across A/B OS updates with no
# `steamos-readonly disable`. Needs `bsdtar`/`tar`, `squashfs-tools` (mksquashfs).
#
# Usage:  bash build-sysext.sh <punktfunk-host-*.pkg.tar.zst>
# Output: punktfunk-host.raw
set -euo pipefail

PKG="${1:?usage: build-sysext.sh <punktfunk-host-*.pkg.tar.zst>}"
[ -f "$PKG" ] || { echo "no such package: $PKG" >&2; exit 1; }
NAME=punktfunk-host

STAGE="$(mktemp -d)"
trap 'rm -rf "$STAGE"' EXIT

# A pacman package is a (zstd) tarball; a sysext only carries /usr (the host /etc, /var are the
# system's). Extract just usr/ from the payload.
if command -v bsdtar >/dev/null 2>&1; then
  bsdtar -C "$STAGE" -xf "$PKG" usr
else
  tar -C "$STAGE" -xf "$PKG" usr
fi

# The marker systemd-sysext requires to merge the image. ID=_any merges onto ANY host os-release
# (SteamOS, Arch, Bazzite); ARCHITECTURE pins it to x86-64 so it's never merged on the wrong arch.
install -d "$STAGE/usr/lib/extension-release.d"
cat > "$STAGE/usr/lib/extension-release.d/extension-release.$NAME" <<EOF
ID=_any
ARCHITECTURE=x86-64
EOF

OUT="$NAME.raw"
rm -f "$OUT"
mksquashfs "$STAGE" "$OUT" -all-root -noappend -quiet
echo "built $OUT"
echo "  install:  sudo cp $OUT /var/lib/extensions/ && sudo systemctl enable --now systemd-sysext"
echo "  then:     systemctl --user enable --now $NAME"