feat(nix-darwin): add setbg script

Sets the background of all spaces on all displays/desktops to an image (passed as a command-line argument) preserving the focused spaces and window after running
Depends on `yabai` (>`System Integrity Protection must be partially disabled.`) and `jq`
Written in `applescript`

modules/nix-darwin/yabai/default.nix

@@ -15,6 +15,12 @@ in
   };
 
   config = mkIf cfg.enable {
+    environment.systemPackages = [
+      (pkgs.callPackage ./setbg {
+        yabai = config.services.yabai.package;
+      })
+    ];
+
     services = {
       yabai = {
         enable = true;

modules/nix-darwin/yabai/setbg/default.nix

@@ -0,0 +1,27 @@
+{ lib
+, writeShellScriptBin
+, symlinkJoin
+, makeWrapper
+, jq
+, yabai
+}:
+
+let
+  # NOTE: passing `${1}` because `${0}` resolves to the `.setbg-wrapped` path
+  setWallpaperUnwrapped =
+    writeShellScriptBin "setbg" ''
+      osascript ${./setbg.scpt} "''${1}"
+    '';
+in
+  symlinkJoin {
+    name = "setbg";
+    paths = [ setWallpaperUnwrapped ];
+    buildInputs = [ makeWrapper ];
+    postBuild = ''
+      wrapProgram $out/bin/setbg \
+        --prefix PATH : ${lib.makeBinPath [
+          jq
+          yabai
+        ]}
+    '';
+  }

modules/nix-darwin/yabai/setbg/setbg.scpt

@@ -0,0 +1,64 @@
+# Get argv
+on run argv
+    # Calculate argc
+    set argc to count of argv
+
+    # Debug mode
+    set debug to true
+
+    tell application "System Events"
+        tell appearance preferences
+            # Prepare wallpaper path
+            if argc < 1
+                log "No argument given, wanted a filepath as the first argument"
+                return
+            end if
+            set filePath to item 1 of argv
+
+            if debug then log "Set filePath to " & filePath
+
+            # Save current focussed spaces and window (to restore afterwards)
+            set visibleSpaceIndices to do shell script "yabai -m query --spaces | jq '.[] | select(.[\"is-visible\"] == true) | .index'"
+            if debug then log "Set visibleSpaceIndices to " & visibleSpaceIndices
+            set focussedWindowId to do shell script "yabai -m query --windows | jq '.[] | select(.[\"has-focus\"] == true) | .id'"
+            if debug then log "Set focussedWindowId to " & focussedWindowId
+
+            # Tell the OS ...
+            tell application "System Events"
+                set displayCount to count of desktops
+                if debug then log "Set displayCount to " & displayCount
+
+                # ... for each display (desktop in Apple's terms) ...
+                repeat with displayIndex from 1 to displayCount
+                    if debug then log "Set displayIndex to " & displayIndex
+
+                    set spaceIds to do shell script "yabai -m query --spaces | jq '.[] | select(.display == " & displayIndex & ") | .index'"
+                    if debug then log "Set spaceIds to " & spaceIds
+
+                    tell desktop displayIndex
+                        # ... iterating through all of its spaces' ids ...
+                        repeat with spaceId in paragraphs of spaceIds
+                            # ... focus each space ...
+                            do shell script "yabai -m space --focus " & spaceId
+                            if debug then log "Focus to space " & spaceId
+
+                            # ... and set its wallpaper to the selected one
+                            set picture to filePath
+                            if debug then log "Set picture to " & picture
+                        end repeat
+                    end tell
+                end repeat
+            end tell
+
+            # Focus back the visible space(s)
+            repeat with visibleSpaceId in paragraphs of visibleSpaceIndices
+                do shell script "yabai -m space --focus " & visibleSpaceId
+                if debug then log "Focus to visible space " & visibleSpaceId
+            end repeat
+
+            # Focus back the original focussed window
+            do shell script "yabai -m window --focus " & focussedWindowId
+            if debug then log "Focus to window " & focussedWindowId
+        end tell
+    end tell
+end run