{
  lib,
  config,
  system,
  pkgs,
  ...
}: let
  inherit (lib.snowfall.system) is-linux;

  cfg = config.marleyos.theme;

  # https://github.com/nix-community/home-manager/blob/master/modules/misc/gtk.nix
  iconThemeType = lib.types.submodule {
    options = {
      package = lib.mkOption {
        type = with lib.types; nullOr package;
        default = null;
        example = pkgs.gnome.adwaita-icon-theme;
        description = ''
          Package providing the icon theme. This package will be installed to
          your profile. If `null` then the theme is assumed to already be
          available in your profile.
        '';
      };

      name = lib.mkOption {
        type = with lib.types; str;
        example = "Adwaita";
        description = "The name of the icon theme within the package.";
      };
    };
  };

  mkFontType = type: default: (lib.mkOption {
    type = lib.types.submodule {
      options = {
        package = lib.mkOption {
          type = with lib.types; package;
          default = default.package;
          description = "The package providing the ${type} font.";
        };

        name = lib.mkOption {
          type = with lib.types; str;
          default = default.name;
          description = "The name of the ${type} font.";
        };

        ligatures = lib.mkOption {
          type = with lib.types; listOf str;
          default = default.ligatures;
          description = "The ligature features to enable for programs that support it.";
        };
      };
    };
    inherit default;
    description = "The ${type} font to use.";
  });
in {
  options.marleyos.theme = {
    icons = lib.mkOption {
      type = with lib.types; nullOr iconThemeType;
      default = null;
      description = "The icon theme to use.";
    };

    fonts = lib.mkOption {
      type = with lib.types;
        submodule {
          options = {
            monospace = mkFontType "monospace" {
              package = pkgs.maple-mono-NF;
              name = "Maple Mono NF";
              ligatures = [];
            };

            sansSerif = mkFontType "sans-serif" {
              package = pkgs.dm-sans;
              name = "DeepMind Sans";
              ligatures = [];
            };

            serif = mkFontType "serif" {
              package = pkgs.eb-garamond;
              name = "EB Garamond";
              ligatures = [];
            };

            emoji = mkFontType "emoji" {
              package = pkgs.whatsapp-emoji-font;
              name = "Apple Color Emoji";
              ligatures = [];
            };
          };
        };
      default = {};
      description = "Default font configuration.";
    };
  };

  config = lib.mkMerge [
    # icons
    (lib.mkIf ((cfg.icons != null) && (is-linux system)) {
      gtk = lib.mkDefault {
        iconTheme = {
          inherit (cfg.icons) name;
          package = lib.mkIf (cfg.icons.package != null) cfg.icons.package;
        };
      };

      services.dunst = lib.mkDefault {
        iconTheme = {
          inherit (cfg.icons) name;
          package = lib.mkIf (cfg.icons.package != null) cfg.icons.package;
        };
      };
    })

    # fonts
    {
      home.packages = [
        cfg.fonts.monospace.package
        cfg.fonts.sansSerif.package
        cfg.fonts.serif.package
        cfg.fonts.emoji.package
      ];

      fonts.fontconfig = lib.mkIf (is-linux system) {
        enable = true;
        defaultFonts = {
          monospace = [cfg.fonts.monospace.name];
          sansSerif = [cfg.fonts.sansSerif.name];
          serif = [cfg.fonts.serif.name];
          emoji = [cfg.fonts.emoji.name];
        };
      };
    }
  ];
}