# Take apart InstallAssistant.pkg on Linux:
#   installer-app.tar  "Install macOS <name>.app" skeleton (Payload, pbzx+cpio)
#   installer.json     byte offsets of SharedSupport.dmg inside the pkg
#   app-name           e.g. "Install macOS Tahoe.app"
# The 18 GB SharedSupport.dmg is never copied on the host; makeImage exposes that
# byte range of the pkg as a raw disk and the recovery script copies it into the app.
{ pkgs, lib, ... }:
{ name, pkg }:
pkgs.runCommand "${name}-installer-payload" {
  nativeBuildInputs = with pkgs; [ xar pbzx cpio python3 gnutar ];
} ''
  mkdir -p $out
  xar --dump-toc=toc.xml -f ${pkg}
  python3 ${./xar-toc.py} toc.xml ${pkg} > $out/installer.json
  grep -q '"SharedSupport.dmg"' $out/installer.json || { echo "no SharedSupport.dmg in pkg"; exit 1; }
  grep -A4 '"SharedSupport.dmg"' $out/installer.json | grep -q '"encoding": "application/octet-stream"' \
    || { echo "SharedSupport.dmg is compressed inside the xar, cannot map it as a disk"; exit 1; }

  echo "=== vmix: extracting installer app skeleton ==="
  xar -x -f ${pkg} Payload
  mkdir root
  (cd root && pbzx -n ../Payload | cpio -idm --quiet)
  APP=$(ls root/Applications | grep -E '^Install macOS.*\.app$' | head -1)
  [ -n "$APP" ] || { echo "installer app not found in Payload"; ls -R root | head; exit 1; }
  echo "$APP" > $out/app-name
  tar -C root/Applications -cf $out/installer-app.tar "$APP"
  ls -la $out
''