zones/*: Deduplicate `mkSerial` functionHEADmain

1 files changed, 39 insertions, 5 deletions

diff --git a/zones/default.nix b/zones/default.nix
index de03a0d..dc3eb9f 100644
--- a/zones/default.nix
+++ b/zones/default.nix
@@ -1,6 +1,40 @@
-{lib, ...}: {
-  "vhack.eu" = import ./vhack.eu/zone.nix {inherit lib;};
-  "j-schoeffel.de" = import ./j-schoeffel.de/zone.nix {inherit lib;};
-  "jaki-schoeffel.de" = import ./jaki-schoeffel.de/zone.nix {inherit lib;};
-  "jaki.li" = import ./jaki.li/zone.nix {inherit lib;};
+{lib, ...}: let
+  /*
+  Computes a reasonable value for the DNS serial number from the date of last change
+  and the iteration of that day.
+
+  # Type
+
+  mkSerial :: Number -> Number -> Number -> Number -> Number
+
+  # Arguments
+
+  year
+  : The year of the last change in the format YYYY.
+
+  month
+  : The month of the last change in the format MM.
+
+  day
+  : The day of the last change in the format DD.
+
+  iteration
+  : The number of change on that day. The format should be CC (assuming there are less
+    than 100 changes happening on a day) .
+
+  # Examples
+
+  mkSerial 2025 04 01 01
+  => 2025040101
+  */
+  mkSerial = year: month: day: iteration: let
+    n2 = lib.strings.fixedWidthNumber 2;
+    n4 = lib.strings.fixedWidthNumber 4;
+  in
+    lib.strings.toIntBase10 "${n4 year}${n2 month}${n2 day}${n2 iteration}";
+in {
+  "vhack.eu" = import ./vhack.eu/zone.nix {inherit mkSerial;};
+  "j-schoeffel.de" = import ./j-schoeffel.de/zone.nix {inherit mkSerial;};
+  "jaki-schoeffel.de" = import ./jaki-schoeffel.de/zone.nix {inherit mkSerial;};
+  "jaki.li" = import ./jaki.li/zone.nix {inherit mkSerial;};
 }