Revert "Replace redshift by go-sct"

This reverts commit ade34b3.

I understand now why redshift wasn't working this time. See [this
issue](NixOS/nixpkgs#321121).

home-manager/autorandr.nix

@@ -4,7 +4,7 @@
   # Enable autorandr. Profiles are specific to hosts, so they're not defined here
   programs.autorandr.enable = true;
 
-  # Since I'm using sct, the gamma always varies. It's skipped when detecting changes and applying a profile.
+  # Since I'm using Redshift, the gamma always varies. It's skipped when detecting changes and applying a profile.
   xdg.configFile."autorandr/settings.ini".text = ''
     [config]
     skip-options=gamma

home-manager/home.nix

@@ -33,6 +33,7 @@
     ./pasystray.nix
     ./picom.nix
     ./playerctl.nix
+    ./redshift.nix
     ./ripgrep.nix
     ./rofi.nix
     ./ruby.nix

home-manager/i3.nix

@@ -161,9 +161,6 @@
       # Center floating windows in the workspace in which they appear
       for_window [floating] move position center
 
-      # Launc sct to control color temperature of the screen
-      exec --no-startup-id sct -dayTemp 5500 -nightTemp 3500
-
       # Launch terminal
       # Somehow, this alacritty instance has a bigger font size due to the `Window Scale Factor` being wrong.
       # This issue started to happen when I upgraded to NixOS 24.05 and I don't know why... following alacritty instances

home-manager/redshift.nix

@@ -0,0 +1,25 @@
+# User configuration for redshift
+
+{ pkgs, options, ... }:
+
+{
+  # Install redshift
+  home.packages = [ options.services.redshift.package.value ];
+
+  # Use redshift to adapt screen's color temperature depending on the time of day
+  services.redshift = {
+    enable = true;
+
+    # Use GeoClue2 as location provider
+    provider = "geoclue2";
+
+    # Colour temperature to use at day/night, between 1000 and 25000 K
+    temperature = {
+      day = 5500;
+      night = 3500;
+    };
+
+    # Start the redshift-gtk tray applet
+    tray = true;
+  };
+}

nixos/configuration.nix

@@ -38,6 +38,7 @@
     ./packages.nix
     ./podman.nix
     ./printing.nix
+    ./redshift.nix
     ./udiskie.nix
     ./unclutter.nix
     ./vscode.nix

nixos/packages.nix

@@ -46,8 +46,6 @@
     go_1_21
     # Go Language Server
     unstable.gopls
-    # Control color temperature of the screen based on location and time
-    go-sct
     # For the command make
     gnumake
     # Color picker

nixos/redshift.nix

@@ -0,0 +1,18 @@
+# System configuration for redshift
+
+{ pkgs, ... }:
+
+{
+  # Without this package, redshift-gtk doesn't have an icon.
+  environment.systemPackages = [ pkgs.hicolor-icon-theme ];
+
+  # Start GeoClue2 daemon
+  services.geoclue2.enable = true;
+
+  # Enable location with GeoClue2
+  services.geoclue2.appConfig.redshift = {
+    isAllowed = true;
+    isSystem = false;
+  };
+  location.provider = "geoclue2";
+}