redshift: create module

home/modules/redshift.nix

@@ -0,0 +1,42 @@
+{ lib, config, pkgs, ... }:
+
+let
+  cfg = config.snowhawk.redshift;
+  cfgDir = config.xdg.configHome + "/redshift";
+in
+{
+  options.snowhawk.redshift = {
+    enable = lib.mkEnableOption "redshift home-manager module";
+  };
+
+  config = lib.mkIf cfg.enable {
+    systemd.user.services.redshift = {
+      Unit = {
+        Description = "redshift service";
+        PartOf = [ "graphical-session.target" ];
+      };
+      Service = {
+        Type = "exec";
+        ExecStart =
+          let
+            catFile = file: "$(${pkgs.coreutils}/bin/cat ${file})";
+            toPaths = deg: "${cfgDir}/${deg}";
+            fetchLatLon = lib.right
+              (lib.strings.concatStringsSep ":")
+              (map catFile)
+              (map toPaths)
+              [ "lat" "lon" ];
+          in
+          "${pkgs.redshift}/bin/redshift -l ${fetchLatLon}";
+      };
+      Install = {
+        WantedBy = [ "graphical-session.target" ];
+      };
+    };
+
+    sops.secrets = {
+      "locations/snowhawk/lat".path = "${cfgDir}/lat";
+      "locations/snowhawk/lon".path = "${cfgDir}/lon";
+    };
+  };
+}