feat(spotify_player): add service/program module

modules/services/spotify_player.nix

@@ -0,0 +1,58 @@
+{ lib, config, pkgs, ... }:
+
+with lib;
+let
+  toml = pkgs.formats.toml { };
+  cfg = config.my.services.spotify-player;
+
+  tomlConfig =
+    if cfg.configFile != null
+    then cfg.configFile
+    else toml.generate "app.toml" cfg.config;
+
+  configFolder = pkgs.runCommand "spotify-player-config" { } ''
+    mkdir $out
+    ln -s "${tomlConfig}" $out/app.toml
+  '';
+in
+{
+  options.my.services.spotify-player = {
+    enable = mkEnableOption "spotify_player";
+    config = mkOption {
+      inherit (toml) type;
+      default = { };
+    };
+    configFile = mkOption {
+      type = with types; nullOr path;
+      default = null;
+    };
+    package = mkOption {
+      type = types.package;
+      default = pkgs.spotify-player;
+    };
+  };
+
+  config = mkIf cfg.enable {
+    assertions = [
+      {
+        assertion = cfg.config == { } || cfg.configFile == null;
+        message = "At least one of the options 'config' or 'configFile' must be set.";
+      }
+      {
+        assertion = cfg.config != { } || cfg.configFile != null;
+        message = "Only one of the options 'config' or 'configFile' may be set.";
+      }
+    ];
+    systemd.user.services.spotify-player = {
+      after = [ "graphical-session.target" "network.target" ];
+      partOf = [ "graphical-session.target" ];
+      wantedBy = [ "graphical-session.target" ];
+      serviceConfig = {
+        Type = "forking";
+        Restart = "always";
+        RestartSec = "1s";
+        ExecStart = "${getExe cfg.package} --daemon --config-folder ${configFolder}";
+      };
+    };
+  };
+}