redshift: add module

This module is adapted from the Nixpkgs version.

modules/default.nix

@@ -25,6 +25,7 @@ let
     ./services/keepassx.nix
     ./services/network-manager-applet.nix
     ./services/random-background.nix
+    ./services/redshift.nix
     ./services/taffybar.nix
     ./services/tahoe-lafs.nix
     ./services/udiskie.nix

modules/services/redshift.nix

@@ -0,0 +1,124 @@
+# Adapted from Nixpkgs.
+
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  cfg = config.services.redshift;
+
+in {
+
+  options.services.redshift = {
+    enable = mkOption {
+      type = types.bool;
+      default = false;
+      example = true;
+      description = ''
+        Enable Redshift to change your screen's colour temperature depending on
+        the time of day.
+      '';
+    };
+
+    latitude = mkOption {
+      type = types.str;
+      description = ''
+        Your current latitude, between
+        <literal>-90.0</literal> and <literal>90.0</literal>.
+      '';
+    };
+
+    longitude = mkOption {
+      type = types.str;
+      description = ''
+        Your current longitude, between
+        between <literal>-180.0</literal> and <literal>180.0</literal>.
+      '';
+    };
+
+    temperature = {
+      day = mkOption {
+        type = types.int;
+        default = 5500;
+        description = ''
+          Colour temperature to use during the day, between
+          <literal>1000</literal> and <literal>25000</literal> K.
+        '';
+      };
+      night = mkOption {
+        type = types.int;
+        default = 3700;
+        description = ''
+          Colour temperature to use at night, between
+          <literal>1000</literal> and <literal>25000</literal> K.
+        '';
+      };
+    };
+
+    brightness = {
+      day = mkOption {
+        type = types.str;
+        default = "1";
+        description = ''
+          Screen brightness to apply during the day,
+          between <literal>0.1</literal> and <literal>1.0</literal>.
+        '';
+      };
+      night = mkOption {
+        type = types.str;
+        default = "1";
+        description = ''
+          Screen brightness to apply during the night,
+          between <literal>0.1</literal> and <literal>1.0</literal>.
+        '';
+      };
+    };
+
+    package = mkOption {
+      type = types.package;
+      default = pkgs.redshift;
+      defaultText = "pkgs.redshift";
+      description = ''
+        redshift derivation to use.
+      '';
+    };
+
+    extraOptions = mkOption {
+      type = types.listOf types.str;
+      default = [];
+      example = [ "-v" "-m randr" ];
+      description = ''
+        Additional command-line arguments to pass to
+        <command>redshift</command>.
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    systemd.user.services.redshift = {
+      Unit = {
+        Description = "Redshift colour temperature adjuster";
+      };
+
+      Install = {
+        WantedBy = [ "graphical-session.target" ];
+      };
+
+      Service = {
+        ExecStart =
+          let
+            args = [
+              "-l ${cfg.latitude}:${cfg.longitude}"
+              "-t ${toString cfg.temperature.day}:${toString cfg.temperature.night}"
+              "-b ${toString cfg.brightness.day}:${toString cfg.brightness.night}"
+            ] ++ cfg.extraOptions;
+          in
+            "${cfg.package}/bin/redshift ${concatStringsSep " " args}";
+        RestartSec = 3;
+        Restart = "always";
+      };
+    };
+  };
+
+}