Add forget option

backup.nix

@@ -28,6 +28,11 @@ let
           echo "$output"
         fi
       done
+      if [ "$BACKUP_FORGET" -eq 1 ]; then
+        echo "Removing old backups"
+        output=$(restic forget -d 7 -w 4 -m 6 --keep-within 1d --prune)
+        echo "$output"
+      fi
       exit "$exit_code";
     '';
   };
@@ -60,6 +65,11 @@ in
       default = 0;
       description = "Randomized delay in seconds to spread out backups.";
     };
+    forget = lib.mkOption {
+      type = lib.types.bool;
+      default = true;
+      description = "Run restic forget after backup.";
+    };
   };
   config = lib.mkIf cfg.enable {
     systemd.services."backup-helper" = {
@@ -69,6 +79,7 @@ in
         {
           RESTIC_REPOSITORY = cfg.restic-repository;
           BACKUP_HELPER_DIRS = lib.strings.concatStringsSep "," cfg.backup-dirs;
+          BACKUP_FORGET = if cfg.forget then "1" else "0";
         }
         // lib.attrsets.optionalAttrs (builtins.hasAttr "password-file" cfg) {
           RESTIC_PASSWORD_FILE = cfg.password-file;