nixos/apps/zen.nix

#./apps/zen.nix
{ inputs, pkgs, lib, config, ... }:
let
  # Autoconfig (mozilla.cfg) runs privileged JS in the parent process at
  # startup — the only scriptable way into chrome, since Gecko has no reload
  # for userChrome.css and Zen exposes no command for one.
  #
  # So don't use userChrome.css at all for the wallpaper theme. Register
  # <profile>/chrome/zen-theme.css as a style-sheet-service USER_SHEET here
  # and re-register it under a cache-busting URI whenever its mtime moves —
  # that is what makes a `theme-apply` switch land in a running Zen
  # (settings/theming.nix writes that file on every switch). A separate file,
  # not userChrome.css: the legacy loader would hold its own copy of the same
  # sheet and the two would race on cascade order.
  themeHotReload = ''
    try {
      const { classes: kCc, interfaces: kCi } = Components;
      const sss = kCc["@mozilla.org/content/style-sheet-service;1"]
                    .getService(kCi.nsIStyleSheetService);

      const file = Services.dirsvc.get("ProfD", kCi.nsIFile);
      file.append("chrome");
      file.append("zen-theme.css");
      const base = Services.io.newFileURI(file).spec;
      let live = null;

      const apply = () => {
        if (!file.exists()) return;
        // install(1) stamps the copy with the current time, so mtime alone
        // distinguishes one wallpaper's sheet from the next.
        const stamp = String(file.lastModifiedTime);
        if (stamp === live) return;
        // A fresh query string dodges the CSS loader's per-URI cache; without
        // it a re-register would hand back the sheet parsed at startup.
        sss.loadAndRegisterSheet(Services.io.newURI(base + "?" + stamp),
                                 sss.USER_SHEET);
        if (live !== null) {
          const old = Services.io.newURI(base + "?" + live);
          if (sss.sheetRegistered(old, sss.USER_SHEET))
            sss.unregisterSheet(old, sss.USER_SHEET);
        }
        live = stamp;
      };

      const timer = kCc["@mozilla.org/timer;1"].createInstance(kCi.nsITimer);
      // The observer service holds the only strong reference that keeps the
      // timer (and this closure) off the GC's list for the session.
      Services.obs.addObserver({ timer, observe() {} }, "quit-application");
      timer.initWithCallback({ notify: apply }, 2000,
                             kCi.nsITimer.TYPE_REPEATING_SLACK);
      apply();
    } catch (e) {
      Components.utils.reportError(e);
    }
  '';
in
{
  config = lib.mkIf (lib.elem config.networking.hostName [ "FredOS-Gaming" "FredOS-Macbook" ]) {
    environment.systemPackages = [
      (inputs.zen-browser.packages.${pkgs.stdenv.hostPlatform.system}.default.override {
        extraPrefs = themeHotReload;
      })
    ];
  };
}