nixos/modules: add greenclip user service

nixos/modules/module-list.nix

@@ -422,6 +422,7 @@
   ./services/misc/gollum.nix
   ./services/misc/gpsd.nix
   ./services/misc/headphones.nix
+  ./services/misc/greenclip.nix
   ./services/misc/home-assistant.nix
   ./services/misc/ihaskell.nix
   ./services/misc/irkerd.nix

nixos/modules/services/misc/greenclip.nix

@@ -0,0 +1,31 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.services.greenclip;
+in {
+
+  options.services.greenclip = {
+    enable = mkEnableOption "Whether to enable the greenclip daemon that will listen to selections";
+
+    package = mkOption {
+      type = types.package;
+      default = pkgs.haskellPackages.greenclip;
+      defaultText = "pkgs.haskellPackages.greenclip";
+      description = "greenclip derivation to use.";
+    };
+  };
+
+  config = mkIf cfg.enable {
+    systemd.user.services.greenclip = {
+      enable      = true;
+      description = "greenclip daemon";
+      wantedBy = [ "graphical-session.target" ];
+      after    = [ "graphical-session.target" ];
+      serviceConfig.ExecStart = "${cfg.package}/bin/greenclip daemon";
+    };
+
+    environment.systemPackages = [ cfg.package ];
+  };
+}