templates/system/modules/ui/desktops/common.nix

# Common desktop environment modules
{
  pkgs,
  config,
  lib,
  ...
}:

let
  cfg = config.aux.system.ui.desktops;
in
{
  options = {
    aux.system.ui.desktops = {
      enable = lib.mkEnableOption (lib.mdDoc "Enables base desktop environment support.");
      xkb = lib.mkOption {
        description = "The keyboard layout to use by default. Defaults to us.";
        type = lib.types.attrs;
        default = {
          layout = "us";
          variant = "";
        };
      };
      displayManager = lib.mkOption {
        description = "The display manager to use to start a desktop session.";
        type = lib.types.enum [
          "gdm"
          "lightdm"
          "sddm"
          "sddm_wayland"
        ];
      };
    };
  };

  config = lib.mkIf cfg.enable {
    aux.system = {
      bluetooth.enable = true;
      ui.audio.enable = true;
    };

    boot = {
      # Enable Plymouth for graphical bootsplash.
      plymouth = {
        enable = true;
        theme = "bgrt";
      };

      # Add kernel parameters
      kernelParams = [ "quiet" ];
    };

    services = {
      # Configure the xserver
      xserver = {
        # Enable the X11 windowing system.
        enable = true;

        # Configure keymap in X11
        xkb = config.aux.system.ui.desktops.xkb;

        # Set the display manager
        displayManager = {
          gdm.enable = (cfg.displayManager == "gdm");
          lightdm.enable = (cfg.displayManager == "lightdm");
        };
      };

      displayManager = {
        sddm.enable = (cfg.displayManager == "sddm");
        sddm.wayland.enable = (cfg.displayManager == "sddm_wayland");
      };

      # Enable touchpad support (enabled by default in most desktop managers, buuuut just in case).
      libinput.enable = true;
    };

    # Support for AppImage files
    programs.appimage = {
      enable = true;
      binfmt = true;
    };

    # Install full GStreamer capabilities.
    # References: 
    #   https://wiki.nixos.org/wiki/GStreamer
    #   https://github.com/NixOS/nixpkgs/issues/195936
    environment = {
      sessionVariables.GST_PLUGIN_SYSTEM_PATH_1_0 = lib.makeSearchPathOutput "lib" "lib/gstreamer-1.0" (
        with pkgs.gst_all_1;
        [
          gstreamer
          gst-plugins-base
          gst-plugins-good
          gst-plugins-bad
          gst-plugins-ugly
          gst-libav
          gst-vaapi
        ]
      );
    };
  };
}