hosts.argon: enable docker auto prune timer

Author: Gerschtli

hosts/argon/configuration.nix

@@ -14,7 +14,11 @@
 
     base.server.enable = true;
 
-    programs.docker.enable = true;
+    programs.docker = {
+      enable = true;
+
+      autoPrune.enable = true;
+    };
 
     services = {
       backup.enable = true;

nixos/programs/docker.nix

@@ -4,6 +4,8 @@ let
   inherit (lib)
     mkEnableOption
     mkIf
+    mkOption
+    types
     ;
 
   cfg = config.custom.programs.docker;
@@ -15,7 +17,21 @@ in
 
   options = {
 
-    custom.programs.docker.enable = mkEnableOption "docker";
+    custom.programs.docker = {
+      enable = mkEnableOption "docker";
+
+      autoPrune = {
+        enable = mkEnableOption "docker system prune cronjob";
+
+        interval = mkOption {
+          type = types.str;
+          default = "Tue *-*-* 03:30:00";
+          description = ''
+            Systemd calendar expression when to run docker system prune. See {manpage}`systemd.time(7)`.
+          '';
+        };
+      };
+    };
 
   };
 
@@ -26,7 +42,15 @@ in
 
     users.users.tobias.extraGroups = [ "docker" ];
 
-    virtualisation.docker.enable = true;
+    virtualisation.docker = {
+      enable = true;
+
+      autoPrune = {
+        inherit (cfg.autoPrune) enable;
+        flags = [ "--all" ];
+        dates = cfg.autoPrune.interval;
+      };
+    };
 
   };