default.nix

{ writeShellApplication
, bundle
, squashfsTools
, gnutar
, pigz
, coreutils
, findutils
, closureInfo
, pv
,
}:

let
  diskClosureInfo = closureInfo { rootPaths = [ bundle ]; };
in
writeShellApplication {
  name = "disk-script";
  runtimeInputs = [
    coreutils
    findutils
    gnutar
    squashfsTools
    pigz
    pv
  ];
  text = ''
    set -x
    TMP_DIR=$(mktemp -d)

    cd "$TMP_DIR"

    root="$TMP_DIR/root"
    diskImage="$TMP_DIR/disk.sqsh"
    tarball="$TMP_DIR/disk.sqsh.tar.gz"

    (
        mkdir -p "$root/nix/store" "$root/etc/nixmodules"

        cp --archive --reflink=auto "${bundle}/etc/nixmodules/"* "$root/etc/nixmodules"

        SECONDS=0
        xargs -P "$(nproc)" cp -a --reflink=auto -t "$root/nix/store/" < "${diskClosureInfo}/store-paths"
        echo "xargs copy took $SECONDS seconds" >&2

        echo "making squashfs..."
        SECONDS=0
        mksquashfs "$root" "$diskImage" -force-uid 11000 -force-gid 11000 -comp lz4 -b 1M
        echo "mksquashfs took $SECONDS seconds" >&2

        SECONDS=0
        tar --use-compress-program="pigz --best --recursive | pv" -Scf "$tarball" disk.sqsh 
        echo "tar took $SECONDS seconds" >&2

        echo Tarball created at "$tarball" >&2
    ) 1>&2

    echo "$tarball"
  '';
}