home-manager/modules/services/linux-wallpaperengine.nix

{
  config,
  lib,
  pkgs,
  ...
}:
let
  inherit (lib) mkOption types;

  cfg = config.services.linux-wallpaperengine;

in
{
  meta.maintainers = [ lib.hm.maintainers.ckgxrg ];

  options.services.linux-wallpaperengine = {
    enable = lib.mkEnableOption "linux-wallpaperengine, an implementation of Wallpaper Engine functionality";

    package = lib.mkPackageOption pkgs "linux-wallpaperengine" { };

    assetsPath = mkOption {
      type = types.nullOr types.path;
      default = null;
      description = "Path to the assets directory.";
    };

    clamping = mkOption {
      type = types.nullOr (
        types.enum [
          "clamp"
          "border"
          "repeat"
        ]
      );
      default = null;
      description = "Clamping mode for all wallpapers.";
    };

    wallpapers = mkOption {
      type = types.listOf (
        types.submodule {
          options = {
            monitor = mkOption {
              type = types.str;
              description = "Which monitor to display the wallpaper.";
            };

            wallpaperId = mkOption {
              type = types.str;
              description = "Wallpaper ID to be used.";
            };

            extraOptions = mkOption {
              type = types.listOf types.str;
              default = [ ];
              description = "Extra arguments to pass to the linux-wallpaperengine command for this wallpaper.";
            };

            scaling = mkOption {
              type = types.nullOr (
                types.enum [
                  "stretch"
                  "fit"
                  "fill"
                  "default"
                ]
              );
              default = null;
              description = "Scaling mode for this wallpaper.";
            };

            fps = mkOption {
              type = types.nullOr types.int;
              default = null;
              description = "Limits the FPS to a given number.";
            };

            audio = {
              silent = mkOption {
                type = types.bool;
                default = false;
                description = "Mutes all sound of the wallpaper.";
              };

              automute = mkOption {
                type = types.bool;
                default = true;
                description = "Automute when another app is playing sound.";
              };

              processing = mkOption {
                type = types.bool;
                default = true;
                description = "Enables audio processing for background.";
              };
            };
          };
        }
      );
      default = [ ];
      description = "Define wallpapers.";
    };
  };

  config = lib.mkIf cfg.enable {
    assertions = [
      (lib.hm.assertions.assertPlatform "services.linux-wallpaperengine" pkgs lib.platforms.linux)
      ({
        assertion = cfg.wallpapers != null;
        message = "linux-wallpaperengine: You must set at least one wallpaper";
      })
    ];

    home.packages = [ cfg.package ];

    systemd.user.services."linux-wallpaperengine" =
      let
        args = lib.lists.forEach cfg.wallpapers (
          each:
          lib.concatStringsSep " " (
            lib.cli.toGNUCommandLine { } {
              screen-root = each.monitor;
              inherit (each) scaling fps;
              silent = each.audio.silent;
              noautomute = !each.audio.automute;
              no-audio-processing = !each.audio.processing;
            }
            ++ each.extraOptions
          )
          # This has to be the last argument in each group
          + " --bg ${each.wallpaperId}"
        );
      in
      {
        Unit = {
          Description = "Implementation of Wallpaper Engine on Linux";
          After = [ "graphical-session.target" ];
          PartOf = [ "graphical-session.target" ];
        };
        Service = {
          ExecStart =
            lib.getExe cfg.package
            + (lib.optionalString (cfg.assetsPath != null) " --assets-dir ${cfg.assetsPath} ")
            + (lib.optionalString (cfg.clamping != null) "--clamping ${cfg.clamping} ")
            + (lib.strings.concatStringsSep " " args);
          Restart = "on-failure";
        };
        Install = {
          WantedBy = [ "graphical-session.target" ];
        };
      };
  };
}