restic: Make restic prune regularily on fuuko

Closes #41.

machines/fuuko/configuration.nix

@@ -35,6 +35,7 @@
         "/data/misc"
         "/data/torrent"
       ];
+      prune = true;
     };
     unfree.allowSoftware = true;
   };

modules/restic/system.nix

@@ -64,6 +64,7 @@ in
       type = lib.types.nullOr lib.types.int;
       default = 1500;
     };
+    prune = lib.mkEnableOption "pruning";
   };
 
   config = lib.mkIf cfg.enable {
@@ -98,6 +99,25 @@ in
       "IOSchedulingPriority" = 7;
     };
 
+    services.restic.backups.system-prune = lib.mkIf cfg.prune {
+      inherit repository;
+      passwordFile = config.sops.secrets.restic-password.path;
+      s3CredentialsFile = config.sops.secrets.restic-s3.path;
+      timerConfig = {
+        OnCalendar = "*-1/2-07 03:00:00";
+        RandomizedDelaySec = "4h";
+      };
+      paths = [ ];
+      pruneOpts = [
+        "--keep-daily 7"
+        "--keep-monthly 12"
+        "--keep-weekly 5"
+        "--keep-yearly 10"
+        "--tag system"
+        "--verbose"
+      ] ++ lib.optional (cfg.uploadLimit != null) "--limit-upload=${toString cfg.uploadLimit}";
+    };
+
     environment.systemPackages = [
       authScript
     ];