nixos/apps/helium.nix

#./apps/helium.nix
{ inputs, pkgs, lib, config, ... }:
let
  upstream = inputs.helium-browser.packages.${pkgs.stdenv.hostPlatform.system}.default;

  # Helium is ungoogled-chromium, so there is no userChrome.css to render a
  # template into the way zen does. Its one themeable surface is chromium's
  # GTK mode: with extensions.theme.system_theme = 1 (ui::SystemTheme::kGtk)
  # the frame, tabstrip and omnibox come from the GTK3 theme, and chromium
  # subscribes to notify::gtk-theme-name — so the gsettings flip at the end of
  # theme-apply recolours a RUNNING helium, the same as nemo. Nothing
  # per-wallpaper has to be generated for it.
  #
  # browser.custom_chrome_frame = false is chromium's "Use system title bar and
  # borders". Hyprland draws no titlebar, so this only drops chromium's own
  # frame, rounded corners and shadow margin — the window fills its tile.
  #
  # Both are profile prefs and chromium rewrites Preferences from memory on
  # exit; no enterprise policy covers either, so there is no declarative way
  # in. Patch the file just before launch instead: helium is then either not
  # running, and the write sticks, or already running with the prefs applied
  # and this process only forwards its arguments to that instance.
  seedPrefs = pkgs.writeShellScript "helium-seed-prefs" ''
    prefs="$HOME/.config/net.imput.helium/Default/Preferences"
    [ -f "$prefs" ] || exit 0
    ${pkgs.jq}/bin/jq -c '
        .extensions.theme.system_theme = 1
      | .browser.custom_chrome_frame = false
    ' "$prefs" > "$prefs.fred" && mv "$prefs.fred" "$prefs" || rm -f "$prefs.fred"
  '';
in
{
  config = lib.mkIf (lib.elem config.networking.hostName [ "FredOS-Gaming" "FredOS-Macbook" ]) {
    environment.systemPackages = [
      (pkgs.symlinkJoin {
        name = "helium-themed";
        paths = [ upstream ];
        nativeBuildInputs = [ pkgs.makeWrapper ];
        # `|| true` is load-bearing: wrapProgram's wrapper runs under `bash -e`,
        # so an unreadable or half-written Preferences would stop the browser
        # from starting at all rather than just skipping the theming.
        postBuild = ''
          wrapProgram $out/bin/helium --run '${seedPrefs} || true'

          # A broken filter here is invisible until the browser quietly never
          # follows the theme, so patch a stub profile at build time and assert.
          (
            export HOME=$(mktemp -d)
            mkdir -p "$HOME/.config/net.imput.helium/Default"
            echo '{"browser":{"custom_chrome_frame":true}}' \
              > "$HOME/.config/net.imput.helium/Default/Preferences"
            ${seedPrefs}
            ${pkgs.jq}/bin/jq -e '.extensions.theme.system_theme == 1
                                  and .browser.custom_chrome_frame == false' \
              "$HOME/.config/net.imput.helium/Default/Preferences" > /dev/null
          )
        '';
      })
    ];
  };
}