Add daily wallpaper module for macOS

hosts/mba/configuration.nix

@@ -14,5 +14,11 @@
     max-free = ${toString (1024 * 1024 * 1024)}
   '';
 
+  services.wallpaper = {
+    enable = true;
+    interval = "daily";
+    category = "nature";
+  };
+
   system.stateVersion = 5;
 }

hosts/mba/default.nix

@@ -7,6 +7,7 @@ nix-darwin.lib.darwinSystem {
     ({ lib, ... }: { nix.settings.auto-optimise-store = lib.mkForce false; }) # TODO https://github.com/NixOS/nix/issues/7273
     self.darwinModules.auto-upgrade
     self.darwinModules.default
+    self.darwinModules.wallpaper
     self.modules.default
   ];
 }

modules/nix-darwin/default.nix

@@ -1,4 +1,5 @@
 { ... }: {
   auto-upgrade = import ./auto-upgrade.nix;
+  wallpaper = import ./wallpaper.nix;
   default = import ./configuration.nix;
 }

modules/nix-darwin/wallpaper.nix

@@ -0,0 +1,48 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+  options.services.wallpaper = {
+    enable = mkEnableOption "Automatic wallpaper changing service";
+
+    interval = mkOption {
+      type = types.str;
+      default = "daily";
+      description = "How often to change the wallpaper (daily, hourly)";
+    };
+
+    category = mkOption {
+      type = types.str;
+      default = "nature";
+      description = "Category of images to fetch from Unsplash";
+    };
+  };
+
+  config = mkIf config.services.wallpaper.enable {
+    environment.systemPackages = with pkgs; [
+      darwin.apple_sdk.frameworks.CoreServices
+    ];
+
+    launchd.agents.change-wallpaper = {
+      serviceConfig = {
+        ProgramArguments = [
+          "/bin/sh"
+          "-c"
+          ''
+            WALLPAPER_URL="https://source.unsplash.com/random/3840x2160/?${config.services.wallpaper.category}"
+            WALLPAPER_PATH="/tmp/wallpaper.jpg"
+            curl -L "$WALLPAPER_URL" -o "$WALLPAPER_PATH"
+            osascript -e "tell application \"Finder\" to set desktop picture to POSIX file \"$WALLPAPER_PATH\""
+          ''
+        ];
+        StartCalendarInterval = (if config.services.wallpaper.interval == "hourly"
+        then [{ Minute = 0; }]
+        else [{ Hour = 0; Minute = 0; }]);
+        RunAtLoad = true;
+        StandardErrorPath = "/tmp/change-wallpaper.err";
+        StandardOutPath = "/tmp/change-wallpaper.out";
+      };
+    };
+  };
+}