graphical-client: add wallpapers

If I find more I like, I'll add them here, I guess. For the moment, there's
just the one.

nix/pkgs/default.nix

@@ -27,5 +27,6 @@
   alertmanager-discord = pkgs.callPackage ./alertmanager-discord.nix {};
   prometheus-snmp-config = import ./prometheus-snmp-config args;
   flameshot = pkgs.libsForQt5.callPackage ./flameshot {};
+  lukegb-wallpapers = pkgs.callPackage ./lukegb-wallpapers {};
 } // (import ./heptapod-runner.nix args)
   // (import ./lightspeed args)

nix/pkgs/lukegb-wallpapers/default.nix

@@ -0,0 +1,14 @@
+# SPDX-FileCopyrightText: 2020 Luke Granger-Brown <depot@lukegb.com>
+#
+# SPDX-License-Identifier: Apache-2.0
+
+{ lib, linkFarm, fetchurl }:
+linkFarm "lukegb-wallpapers" [
+  {
+    name = "lunik1-gruvbox-dark-rainbow.png";
+    path = fetchurl {
+      url = "https://github.com/lunik1/nixos-logo-gruvbox-wallpaper/raw/fce9108e2938eb03d8c7a779bbdafd4663d3bea4/png/gruvbox-dark-rainbow.png";
+      sha256 = "sha256:036gqhbf6s5ddgvfbgn6iqbzgizssyf7820m5815b2gd748jw8zc";
+    };
+  }
+]

ops/nixos/lib/home-manager/graphical-client.nix

@@ -48,6 +48,12 @@
     systemctl --user restart ssh-agent
   '';
 
+  services.random-background = {
+    enable = true;
+    imageDirectory = "${depot.nix.pkgs.lukegb-wallpapers}";
+    interval = null;
+  };
+
   xsession.windowManager.i3 = {
     enable = true;
     config = {